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Subject: Re: [PATCH v3 2/4] dmaengine: tegra: Add tegra gpcdma driver
To:     Akhil R <akhilrajeev@nvidia.com>, <rgumasta@nvidia.com>
CC:     <dan.j.williams@intel.com>, <dmaengine@vger.kernel.org>,
        <kyarlagadda@nvidia.com>, <ldewangan@nvidia.com>,
        <linux-kernel@vger.kernel.org>, <linux-tegra@vger.kernel.org>,
        <p.zabel@pengutronix.de>, <thierry.reding@gmail.com>,
        <vkoul@kernel.org>, Pavan Kunapuli <pkunapuli@nvidia.com>
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From:   Jon Hunter <jonathanh@nvidia.com>
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Date:   Wed, 1 Sep 2021 21:56:15 +0100
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On 27/08/2021 07:04, Akhil R wrote:
> Adding GPC DMA controller driver for Tegra186 and Tegra194. The driver
> supports dma transfers between memory to memory, IO peripheral to memory
> and memory to IO peripheral.
> 
> Signed-off-by: Pavan Kunapuli <pkunapuli@nvidia.com>
> Signed-off-by: Rajesh Gumasta <rgumasta@nvidia.com>
> Signed-off-by: Akhil R <akhilrajeev@nvidia.com>
> ---
>   drivers/dma/Kconfig         |   12 +
>   drivers/dma/Makefile        |    1 +
>   drivers/dma/tegra-gpc-dma.c | 1343 +++++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 1356 insertions(+)
>   create mode 100644 drivers/dma/tegra-gpc-dma.c
> 
> diff --git a/drivers/dma/Kconfig b/drivers/dma/Kconfig
> index 39b5b46..9d1d93d 100644
> --- a/drivers/dma/Kconfig
> +++ b/drivers/dma/Kconfig
> @@ -632,6 +632,18 @@ config TEGRA210_ADMA
>   	  peripheral and vice versa. It does not support memory to
>   	  memory data transfer.
>   
> +config TEGRA_GPC_DMA
> +	tristate "NVIDIA Tegra GPC DMA support"
> +	depends on ARCH_TEGRA_186_SOC || ARCH_TEGRA_194_SOC || COMPILE_TEST
> +	select DMA_ENGINE
> +	help
> +	  Support for the NVIDIA Tegra186 and Tegra194 GPC DMA controller
> +	  driver. The DMA controller has multiple DMA channels which can
> +	  be configured for different peripherals like UART, SPI, etc
> +	  which are on APB bus.
> +	  This DMA controller transfers data from memory to peripheral FIFO
> +	  or vice versa. It also supports memory to memory data transfer.
> +
>   config TIMB_DMA
>   	tristate "Timberdale FPGA DMA support"
>   	depends on MFD_TIMBERDALE || COMPILE_TEST
> diff --git a/drivers/dma/Makefile b/drivers/dma/Makefile
> index aa69094..943e8d7 100644
> --- a/drivers/dma/Makefile
> +++ b/drivers/dma/Makefile
> @@ -73,6 +73,7 @@ obj-$(CONFIG_S3C24XX_DMAC) += s3c24xx-dma.o
>   obj-$(CONFIG_TXX9_DMAC) += txx9dmac.o
>   obj-$(CONFIG_TEGRA20_APB_DMA) += tegra20-apb-dma.o
>   obj-$(CONFIG_TEGRA210_ADMA) += tegra210-adma.o
> +obj-$(CONFIG_TEGRA_GPC_DMA) += tegra-gpc-dma.o
>   obj-$(CONFIG_TIMB_DMA) += timb_dma.o
>   obj-$(CONFIG_UNIPHIER_MDMAC) += uniphier-mdmac.o
>   obj-$(CONFIG_UNIPHIER_XDMAC) += uniphier-xdmac.o
> diff --git a/drivers/dma/tegra-gpc-dma.c b/drivers/dma/tegra-gpc-dma.c
> new file mode 100644
> index 0000000..d990121
> --- /dev/null
> +++ b/drivers/dma/tegra-gpc-dma.c
> @@ -0,0 +1,1343 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * DMA driver for Nvidia's Tegra186 and Tegra194 GPC DMA controller.
> + *
> + * Copyright (c) 2014-2020, NVIDIA CORPORATION.  All rights reserved.
> + */
> +
> +#include <linux/bitops.h>
> +#include <linux/delay.h>
> +#include <linux/dmaengine.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/err.h>
> +#include <linux/init.h>
> +#include <linux/interrupt.h>
> +#include <linux/io.h>
> +#include <linux/iopoll.h>
> +#include <linux/mm.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_device.h>
> +#include <linux/of_dma.h>
> +#include <linux/platform_device.h>
> +#include <linux/pm.h>
> +#include <linux/reset.h>
> +#include <linux/slab.h>
> +#include <linux/version.h>
> +#include <dt-bindings/memory/tegra186-mc.h>
> +#include "virt-dma.h"
> +
> +/* CSR register */
> +#define TEGRA_GPCDMA_CHAN_CSR			0x00
> +#define TEGRA_GPCDMA_CSR_ENB			BIT(31)
> +#define TEGRA_GPCDMA_CSR_IE_EOC			BIT(30)
> +#define TEGRA_GPCDMA_CSR_ONCE			BIT(27)
> +
> +#define TEGRA_GPCDMA_CSR_FC_MODE		GENMASK(25, 24)
> +#define TEGRA_GPCDMA_CSR_FC_MODE_NO_MMIO	\
> +					FIELD_PREP(TEGRA_GPCDMA_CSR_FC_MODE, 0)
> +#define TEGRA_GPCDMA_CSR_FC_MODE_ONE_MMIO	\
> +					FIELD_PREP(TEGRA_GPCDMA_CSR_FC_MODE, 1)
> +#define TEGRA_GPCDMA_CSR_FC_MODE_TWO_MMIO	\
> +					FIELD_PREP(TEGRA_GPCDMA_CSR_FC_MODE, 2)
> +#define TEGRA_GPCDMA_CSR_FC_MODE_FOUR_MMIO	\
> +					FIELD_PREP(TEGRA_GPCDMA_CSR_FC_MODE, 3)
> +
> +#define TEGRA_GPCDMA_CSR_DMA			GENMASK(23, 21)
> +#define TEGRA_GPCDMA_CSR_DMA_IO2MEM_NO_FC	\
> +					FIELD_PREP(TEGRA_GPCDMA_CSR_DMA, 0)
> +#define TEGRA_GPCDMA_CSR_DMA_IO2MEM_FC		\
> +					FIELD_PREP(TEGRA_GPCDMA_CSR_DMA, 1)
> +#define TEGRA_GPCDMA_CSR_DMA_MEM2IO_NO_FC	\
> +					FIELD_PREP(TEGRA_GPCDMA_CSR_DMA, 2)
> +#define TEGRA_GPCDMA_CSR_DMA_MEM2IO_FC		\
> +					FIELD_PREP(TEGRA_GPCDMA_CSR_DMA, 3)
> +#define TEGRA_GPCDMA_CSR_DMA_MEM2MEM		\
> +					FIELD_PREP(TEGRA_GPCDMA_CSR_DMA, 4)
> +#define TEGRA_GPCDMA_CSR_DMA_FIXED_PAT		\
> +					FIELD_PREP(TEGRA_GPCDMA_CSR_DMA, 6)
> +
> +#define TEGRA_GPCDMA_CSR_REQ_SEL_MASK		GENMASK(20, 16)
> +#define TEGRA_GPCDMA_CSR_REQ_SEL_UNUSED		\
> +					FIELD_PREP(TEGRA_GPCDMA_CSR_REQ_SEL_MASK, 4)
> +#define TEGRA_GPCDMA_CSR_IRQ_MASK			BIT(15)
> +#define TEGRA_GPCDMA_CSR_WEIGHT				GENMASK(13, 10)
> +
> +/* STATUS register */
> +#define TEGRA_GPCDMA_CHAN_STATUS			0x004
> +#define TEGRA_GPCDMA_STATUS_BUSY			BIT(31)
> +#define TEGRA_GPCDMA_STATUS_ISE_EOC			BIT(30)
> +#define TEGRA_GPCDMA_STATUS_PING_PONG		BIT(28)
> +#define TEGRA_GPCDMA_STATUS_DMA_ACTIVITY	BIT(27)
> +#define TEGRA_GPCDMA_STATUS_CHANNEL_PAUSE	BIT(26)
> +#define TEGRA_GPCDMA_STATUS_CHANNEL_RX		BIT(25)
> +#define TEGRA_GPCDMA_STATUS_CHANNEL_TX		BIT(24)
> +#define TEGRA_GPCDMA_STATUS_IRQ_INTR_STA	BIT(23)
> +#define TEGRA_GPCDMA_STATUS_IRQ_STA			BIT(21)
> +#define TEGRA_GPCDMA_STATUS_IRQ_TRIG_STA	BIT(20)
> +
> +#define TEGRA_GPCDMA_CHAN_CSRE				0x008
> +#define TEGRA_GPCDMA_CHAN_CSRE_PAUSE		BIT(31)
> +
> +/* Source address */
> +#define TEGRA_GPCDMA_CHAN_SRC_PTR			0x00C
> +
> +/* Destination address */
> +#define TEGRA_GPCDMA_CHAN_DST_PTR			0x010
> +
> +/* High address pointer */
> +#define TEGRA_GPCDMA_CHAN_HIGH_ADDR_PTR		0x014
> +#define TEGRA_GPCDMA_HIGH_ADDR_SRC_PTR		GENMASK(7, 0)
> +#define TEGRA_GPCDMA_HIGH_ADDR_DST_PTR		GENMASK(23, 16)
> +
> +/* MC sequence register */
> +#define TEGRA_GPCDMA_CHAN_MCSEQ			0x18
> +#define TEGRA_GPCDMA_MCSEQ_DATA_SWAP	BIT(31)
> +#define TEGRA_GPCDMA_MCSEQ_REQ_COUNT	GENMASK(30, 25)
> +#define TEGRA_GPCDMA_MCSEQ_BURST		GENMASK(24, 23)
> +#define TEGRA_GPCDMA_MCSEQ_BURST_2		\
> +					FIELD_PREP(TEGRA_GPCDMA_MCSEQ_BURST, 0)
> +#define TEGRA_GPCDMA_MCSEQ_BURST_16		\
> +					FIELD_PREP(TEGRA_GPCDMA_MCSEQ_BURST, 3)
> +#define TEGRA_GPCDMA_MCSEQ_WRAP1		GENMASK(22, 20)
> +#define TEGRA_GPCDMA_MCSEQ_WRAP0		GENMASK(19, 17)
> +#define TEGRA_GPCDMA_MCSEQ_WRAP_NONE		0
> +
> +#define TEGRA_GPCDMA_MCSEQ_STREAM_ID1_MASK	GENMASK(13, 7)
> +#define TEGRA_GPCDMA_MCSEQ_STREAM_ID0_MASK	GENMASK(6, 0)
> +
> +/* MMIO sequence register */
> +#define TEGRA_GPCDMA_CHAN_MMIOSEQ			0x01c
> +#define TEGRA_GPCDMA_MMIOSEQ_DBL_BUF		BIT(31)
> +#define TEGRA_GPCDMA_MMIOSEQ_BUS_WIDTH		GENMASK(30, 28)
> +#define TEGRA_GPCDMA_MMIOSEQ_BUS_WIDTH_8	\
> +					FIELD_PREP(TEGRA_GPCDMA_MMIOSEQ_BUS_WIDTH, 0)
> +#define TEGRA_GPCDMA_MMIOSEQ_BUS_WIDTH_16	\
> +					FIELD_PREP(TEGRA_GPCDMA_MMIOSEQ_BUS_WIDTH, 1)
> +#define TEGRA_GPCDMA_MMIOSEQ_BUS_WIDTH_32	\
> +					FIELD_PREP(TEGRA_GPCDMA_MMIOSEQ_BUS_WIDTH, 2)
> +#define TEGRA_GPCDMA_MMIOSEQ_DATA_SWAP		BIT(27)
> +#define TEGRA_GPCDMA_MMIOSEQ_BURST			GENMASK(26, 23)
> +#define TEGRA_GPCDMA_MMIOSEQ_BURST_1		\
> +					FIELD_PREP(TEGRA_GPCDMA_MMIOSEQ_BURST, 0)
> +#define TEGRA_GPCDMA_MMIOSEQ_BURST_2		\
> +					FIELD_PREP(TEGRA_GPCDMA_MMIOSEQ_BURST, 1)
> +#define TEGRA_GPCDMA_MMIOSEQ_BURST_4		\
> +					FIELD_PREP(TEGRA_GPCDMA_MMIOSEQ_BURST, 3)
> +#define TEGRA_GPCDMA_MMIOSEQ_BURST_8		\
> +					FIELD_PREP(TEGRA_GPCDMA_MMIOSEQ_BURST, 7)
> +#define TEGRA_GPCDMA_MMIOSEQ_BURST_16		\
> +					FIELD_PREP(TEGRA_GPCDMA_MMIOSEQ_BURST, 15)
> +#define TEGRA_GPCDMA_MMIOSEQ_MASTER_ID		GENMASK(22, 19)
> +#define TEGRA_GPCDMA_MMIOSEQ_WRAP_WORD		GENMASK(18, 16)
> +#define TEGRA_GPCDMA_MMIOSEQ_MMIO_PROT		GENMASK(8, 7)
> +
> +/* Channel WCOUNT */
> +#define TEGRA_GPCDMA_CHAN_WCOUNT		0x20
> +
> +/* Transfer count */
> +#define TEGRA_GPCDMA_CHAN_XFER_COUNT		0x24
> +
> +/* DMA byte count status */
> +#define TEGRA_GPCDMA_CHAN_DMA_BYTE_STATUS	0x28
> +
> +/* Error Status Register */
> +#define TEGRA_GPCDMA_CHAN_ERR_STATUS		0x30
> +#define TEGRA_GPCDMA_CHAN_ERR_TYPE_SHIFT	(8)
> +#define TEGRA_GPCDMA_CHAN_ERR_TYPE_MASK	(0xF)
> +#define TEGRA_GPCDMA_CHAN_ERR_TYPE(err)	(			\
> +		((err) >> TEGRA_GPCDMA_CHAN_ERR_TYPE_SHIFT) &	\
> +		TEGRA_GPCDMA_CHAN_ERR_TYPE_MASK)
> +#define TEGRA_DMA_BM_FIFO_FULL_ERR		(0xF)
> +#define TEGRA_DMA_PERIPH_FIFO_FULL_ERR		(0xE)
> +#define TEGRA_DMA_PERIPH_ID_ERR			(0xD)
> +#define TEGRA_DMA_STREAM_ID_ERR			(0xC)
> +#define TEGRA_DMA_MC_SLAVE_ERR			(0xB)
> +#define TEGRA_DMA_MMIO_SLAVE_ERR		(0xA)
> +
> +/* Fixed Pattern */
> +#define TEGRA_GPCDMA_CHAN_FIXED_PATTERN		0x34
> +
> +#define TEGRA_GPCDMA_CHAN_TZ			0x38
> +#define TEGRA_GPCDMA_CHAN_TZ_MMIO_PROT_1	BIT(0)
> +#define TEGRA_GPCDMA_CHAN_TZ_MC_PROT_1		BIT(1)
> +
> +#define TEGRA_GPCDMA_CHAN_SPARE			0x3c
> +#define TEGRA_GPCDMA_CHAN_SPARE_EN_LEGACY_FC	BIT(16)
> +
> +/*
> + * If any burst is in flight and DMA paused then this is the time to complete
> + * on-flight burst and update DMA status register.
> + */
> +#define TEGRA_GPCDMA_BURST_COMPLETE_TIME	20
> +#define TEGRA_GPCDMA_BURST_COMPLETION_TIMEOUT	100
> +
> +/* Channel base address offset from GPCDMA base address */
> +#define TEGRA_GPCDMA_CHANNEL_BASE_ADD_OFFSET	0x10000
> +
> +struct tegra_dma;
> +
> +/*
> + * tegra_dma_chip_data Tegra chip specific DMA data
> + * @nr_channels: Number of channels available in the controller.
> + * @channel_reg_size: Channel register size.
> + * @max_dma_count: Maximum DMA transfer count supported by DMA controller.
> + * @hw_support_pause: DMA HW engine support pause of the channel.
> + */
> +struct tegra_dma_chip_data {
> +	int nr_channels;
> +	int channel_reg_size;
> +	int max_dma_count;
> +	bool hw_support_pause;
> +};
> +
> +/* DMA channel registers */
> +struct tegra_dma_channel_regs {
> +	unsigned long csr;
> +	unsigned long src_ptr;
> +	unsigned long dst_ptr;
> +	unsigned long high_addr_ptr;
> +	unsigned long mc_seq;
> +	unsigned long mmio_seq;
> +	unsigned long wcount;
> +	unsigned long fixed_pattern;
> +};
> +
> +/*
> + * tegra_dma_desc: Tegra DMA descriptors which uses virt_dma_desc to
> + * manage client request and keep track of transfer status, callbacks
> + * and request counts etc.
> + */
> +struct tegra_dma_desc {
> +	struct virt_dma_desc vd;
> +	int bytes_requested;
> +	int bytes_transferred;
> +	struct tegra_dma_channel *tdc;
> +	struct tegra_dma_channel_regs ch_regs;
> +};
> +
> +struct tegra_dma_channel;
> +
> +typedef void (*dma_isr_handler)(struct tegra_dma_channel *tdc,
> +				bool to_terminate);
> +
> +/*
> + * tegra_dma_channel: Channel specific information
> + */
> +struct tegra_dma_channel {
> +	struct virt_dma_chan vc;
> +	struct tegra_dma_desc *dma_desc;
> +	char name[30];
> +	bool config_init;
> +	int id;
> +	int irq;
> +	unsigned int stream_id;
> +	unsigned long chan_base_offset;
> +	raw_spinlock_t lock;
> +	bool busy;
> +	bool is_pending;
> +	struct tegra_dma *tdma;
> +	dma_isr_handler isr_handler;
> +	int slave_id;
> +	struct dma_slave_config dma_sconfig;
> +};
> +
> +/*
> + * tegra_dma: Tegra DMA specific information
> + */
> +struct tegra_dma {
> +	struct dma_device dma_dev;
> +	struct device *dev;
> +	void __iomem *base_addr;
> +	const struct tegra_dma_chip_data *chip_data;
> +	struct reset_control *rst;
> +	struct tegra_dma_channel channels[0];
> +};
> +
> +static inline void tdc_write(struct tegra_dma_channel *tdc,
> +			     u32 reg, u32 val)
> +{
> +	writel_relaxed(val, tdc->tdma->base_addr + tdc->chan_base_offset + reg);
> +}
> +
> +static inline u32 tdc_read(struct tegra_dma_channel *tdc, u32 reg)
> +{
> +	return readl_relaxed(tdc->tdma->base_addr + tdc->chan_base_offset + reg);
> +}
> +
> +static inline struct tegra_dma_channel *to_tegra_dma_chan(struct dma_chan *dc)
> +{
> +	return container_of(dc, struct tegra_dma_channel, vc.chan);
> +}
> +
> +static inline struct tegra_dma_desc *vd_to_tegra_dma_desc(struct virt_dma_desc *vd)
> +{
> +	return container_of(vd, struct tegra_dma_desc, vd);
> +}
> +
> +static inline struct device *tdc2dev(struct tegra_dma_channel *tdc)
> +{
> +	return tdc->vc.chan.device->dev;
> +}
> +
> +static void tegra_dma_dump_chan_regs(struct tegra_dma_channel *tdc)
> +{
> +	dev_dbg(tdc2dev(tdc), "DMA Channel %d name %s register dump:\n",
> +		tdc->id, tdc->name);
> +	dev_dbg(tdc2dev(tdc), "CSR %x STA %x CSRE %x SRC %x DST %x\n",
> +		tdc_read(tdc, TEGRA_GPCDMA_CHAN_CSR),
> +		tdc_read(tdc, TEGRA_GPCDMA_CHAN_STATUS),
> +		tdc_read(tdc, TEGRA_GPCDMA_CHAN_CSRE),
> +		tdc_read(tdc, TEGRA_GPCDMA_CHAN_SRC_PTR),
> +		tdc_read(tdc, TEGRA_GPCDMA_CHAN_DST_PTR)
> +	);
> +	dev_dbg(tdc2dev(tdc), "MCSEQ %x IOSEQ %x WCNT %x XFER %x BSTA %x\n",
> +		tdc_read(tdc, TEGRA_GPCDMA_CHAN_MCSEQ),
> +		tdc_read(tdc, TEGRA_GPCDMA_CHAN_MMIOSEQ),
> +		tdc_read(tdc, TEGRA_GPCDMA_CHAN_WCOUNT),
> +		tdc_read(tdc, TEGRA_GPCDMA_CHAN_XFER_COUNT),
> +		tdc_read(tdc, TEGRA_GPCDMA_CHAN_DMA_BYTE_STATUS)
> +	);
> +	dev_dbg(tdc2dev(tdc), "DMA ERR_STA %x\n",
> +		tdc_read(tdc, TEGRA_GPCDMA_CHAN_ERR_STATUS));
> +}
> +
> +static void tegra_dma_desc_free(struct virt_dma_desc *vd)
> +{
> +	struct tegra_dma_desc *dma_desc = vd_to_tegra_dma_desc(vd);
> +	struct tegra_dma_channel *tdc = dma_desc->tdc;
> +	unsigned long flags;
> +
> +	if (dma_desc) {
> +		raw_spin_lock_irqsave(&tdc->lock, flags);
> +		kfree(dma_desc);
> +		raw_spin_unlock_irqrestore(&tdc->lock, flags);
> +	}
> +}


I think that this can be simplified to simply ...

  static void tegra_dma_desc_free(struct virt_dma_desc *vd)
  {
          kfree(container_of(vd, struct tegra_dma_desc, vd));
  }

> +
> +static int tegra_dma_slave_config(struct dma_chan *dc,
> +				  struct dma_slave_config *sconfig)
> +{
> +	struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> +
> +	if (tdc->dma_desc) {

Any reason not to check config_init here instead?

> +		dev_err(tdc2dev(tdc), "Configuration not allowed\n");
> +		return -EBUSY;
> +	}
> +
> +	memcpy(&tdc->dma_sconfig, sconfig, sizeof(*sconfig));
> +	if (tdc->slave_id == -1)
> +		tdc->slave_id = sconfig->slave_id;

How do you ensure that you are not trying to use an ID that is already 
being used? If you look at the tegra210-adma.c driver you will see that 
we have a bit mask for determining if the IDs are in used or not (see 
tx_requests_reserved and rx_requests_reserved).

> +	tdc->config_init = true;
> +	return 0;
> +}
> +
> +static int tegra_dma_pause(struct tegra_dma_channel *tdc)
> +{
> +	u32 val;
> +	int ret;
> +
> +	tdc_write(tdc, TEGRA_GPCDMA_CHAN_CSRE, TEGRA_GPCDMA_CHAN_CSRE_PAUSE);
> +
> +	/* Wait until busy bit is de-asserted */
> +	ret = readl_relaxed_poll_timeout_atomic(tdc->tdma->base_addr +
> +			tdc->chan_base_offset + TEGRA_GPCDMA_CHAN_STATUS,
> +			val,
> +			!(val & TEGRA_GPCDMA_STATUS_BUSY),
> +			TEGRA_GPCDMA_BURST_COMPLETE_TIME,
> +			TEGRA_GPCDMA_BURST_COMPLETION_TIMEOUT);
> +
> +	if (ret)
> +		dev_err(tdc2dev(tdc), "DMA pause timed out\n");
> +
> +	return ret;
> +}
> +
> +static void tegra_dma_stop(struct tegra_dma_channel *tdc)
> +{
> +	u32 csr, status;
> +
> +	csr = tdc_read(tdc, TEGRA_GPCDMA_CHAN_CSR);
> +
> +	/* Disable interrupts */
> +	csr &= ~TEGRA_GPCDMA_CSR_IE_EOC;
> +
> +	/* Disable DMA */
> +	csr &= ~TEGRA_GPCDMA_CSR_ENB;
> +	tdc_write(tdc, TEGRA_GPCDMA_CHAN_CSR, csr);
> +
> +	/* Clear interrupt status if it is there */
> +	status = tdc_read(tdc, TEGRA_GPCDMA_CHAN_STATUS);
> +	if (status & TEGRA_GPCDMA_STATUS_ISE_EOC) {
> +		dev_dbg(tdc2dev(tdc), "%s():clearing interrupt\n", __func__);
> +		tdc_write(tdc, TEGRA_GPCDMA_CHAN_STATUS, status);
> +	}
> +	tdc->busy = false;
> +}
> +
> +static void tegra_dma_start(struct tegra_dma_channel *tdc)
> +{
> +	struct tegra_dma_channel_regs *ch_regs = &tdc->dma_desc->ch_regs;
> +
> +	tdc_write(tdc, TEGRA_GPCDMA_CHAN_WCOUNT, ch_regs->wcount);
> +
> +	tdc_write(tdc, TEGRA_GPCDMA_CHAN_CSR, 0);
> +	tdc_write(tdc, TEGRA_GPCDMA_CHAN_SRC_PTR, ch_regs->src_ptr);
> +	tdc_write(tdc, TEGRA_GPCDMA_CHAN_DST_PTR, ch_regs->dst_ptr);
> +	tdc_write(tdc, TEGRA_GPCDMA_CHAN_HIGH_ADDR_PTR, ch_regs->high_addr_ptr);
> +	tdc_write(tdc, TEGRA_GPCDMA_CHAN_FIXED_PATTERN, ch_regs->fixed_pattern);
> +	tdc_write(tdc, TEGRA_GPCDMA_CHAN_MMIOSEQ, ch_regs->mmio_seq);
> +	tdc_write(tdc, TEGRA_GPCDMA_CHAN_MCSEQ, ch_regs->mc_seq);
> +	tdc_write(tdc, TEGRA_GPCDMA_CHAN_CSRE, 0);
> +	tdc_write(tdc, TEGRA_GPCDMA_CHAN_CSR, ch_regs->csr);
> +
> +	/* Start DMA */
> +	tdc_write(tdc, TEGRA_GPCDMA_CHAN_CSR,
> +		  ch_regs->csr | TEGRA_GPCDMA_CSR_ENB);
> +}
> +
> +static void tdc_start_head_req(struct tegra_dma_channel *tdc)
> +{
> +	struct virt_dma_desc *vdesc;
> +
> +	if (tdc->is_pending)
> +		return;
> +
> +	vdesc = vchan_next_desc(&tdc->vc);
> +	if (!vdesc)
> +		return;
> +
> +	tdc->dma_desc = vd_to_tegra_dma_desc(vdesc);
> +	if (!tdc->dma_desc)
> +		return;
> +
> +	list_del(&vdesc->node);
> +
> +	tdc->is_pending = true;

Is is_pending really needed?

> +	tdc->dma_desc->tdc = tdc;
> +	tegra_dma_start(tdc);

I would combine this function and tegra_dma_start() into a single 
function called tegra_dma_start().

> +	tdc->busy = true;
> +}
> +
> +static void tegra_dma_abort_all(struct tegra_dma_channel *tdc)
> +{
> +	kfree(tdc->dma_desc);
> +	tdc->isr_handler = NULL;
> +}
> +
> +static void handle_once_dma_done(struct tegra_dma_channel *tdc,
> +				 bool to_terminate)

This function name is not very descriptive. Maybe just 
tegra_dma_isr_callback().

> +{
> +	struct tegra_dma_desc *dma_desc;
> +
> +	tdc->busy = false;
> +	dma_desc = tdc->dma_desc;
> +	dma_desc->bytes_transferred += dma_desc->bytes_requested;
> +
> +	vchan_cookie_complete(&tdc->dma_desc->vd);
> +	tdc->is_pending = false;
> +	kfree(tdc->dma_desc);
> +
> +	if (to_terminate)
> +		return;
> +
> +	tdc_start_head_req(tdc);
> +}
> +
> +static void tegra_dma_chan_decode_error(struct tegra_dma_channel *tdc,
> +					unsigned int err_status)
> +{
> +	switch (TEGRA_GPCDMA_CHAN_ERR_TYPE(err_status)) {
> +	case TEGRA_DMA_BM_FIFO_FULL_ERR:
> +		dev_err(tdc->tdma->dev,
> +			"GPCDMA CH%d bm fifo full\n", tdc->id);
> +		break;
> +
> +	case TEGRA_DMA_PERIPH_FIFO_FULL_ERR:
> +		dev_err(tdc->tdma->dev,
> +			"GPCDMA CH%d peripheral fifo full\n", tdc->id);
> +		break;
> +
> +	case TEGRA_DMA_PERIPH_ID_ERR:
> +		dev_err(tdc->tdma->dev,
> +			"GPCDMA CH%d illegal peripheral id\n", tdc->id);
> +		break;
> +
> +	case TEGRA_DMA_STREAM_ID_ERR:
> +		dev_err(tdc->tdma->dev,
> +			"GPCDMA CH%d illegal stream id\n", tdc->id);
> +		break;
> +
> +	case TEGRA_DMA_MC_SLAVE_ERR:
> +		dev_err(tdc->tdma->dev,
> +			"GPCDMA CH%d mc slave error\n", tdc->id);
> +		break;
> +
> +	case TEGRA_DMA_MMIO_SLAVE_ERR:
> +		dev_err(tdc->tdma->dev,
> +			"GPCDMA CH%d mmio slave error\n", tdc->id);
> +		break;
> +
> +	default:
> +		dev_err(tdc->tdma->dev,
> +			"GPCDMA CH%d security violation %x\n", tdc->id,
> +			err_status);
> +	}
> +}
> +
> +static irqreturn_t tegra_dma_isr(int irq, void *dev_id)
> +{
> +	struct tegra_dma_channel *tdc = dev_id;
> +	irqreturn_t ret = IRQ_NONE;
> +	unsigned int err_status;
> +	unsigned long status;
> +
> +	raw_spin_lock(&tdc->lock);
> +
> +	status = tdc_read(tdc, TEGRA_GPCDMA_CHAN_STATUS);
> +	err_status = tdc_read(tdc, TEGRA_GPCDMA_CHAN_ERR_STATUS);
> +
> +	if (err_status) {
> +		tegra_dma_chan_decode_error(tdc, err_status);
> +		tegra_dma_dump_chan_regs(tdc);
> +		tdc_write(tdc, TEGRA_GPCDMA_CHAN_ERR_STATUS, 0xFFFFFFFF);
> +	}
> +
> +	if (status & TEGRA_GPCDMA_STATUS_ISE_EOC) {
> +		tdc_write(tdc, TEGRA_GPCDMA_CHAN_STATUS,
> +			  TEGRA_GPCDMA_STATUS_ISE_EOC);
> +		if (tdc->isr_handler) {
> +			tdc->isr_handler(tdc, false);
> +		} else {
> +			dev_err(tdc->tdma->dev,
> +				"GPCDMA CH%d: status %lx ISR handler absent!\n",
> +				tdc->id, status);
> +			tegra_dma_dump_chan_regs(tdc);
> +		}
> +		ret = IRQ_HANDLED;
> +	}
> +
> +	raw_spin_unlock(&tdc->lock);
> +	return ret;
> +}
> +
> +static void tegra_dma_issue_pending(struct dma_chan *dc)
> +{
> +	struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> +	unsigned long flags;
> +
> +	raw_spin_lock_irqsave(&tdc->lock, flags);
> +
> +	if (!tdc->busy)
> +		if (vchan_issue_pending(&tdc->vc))
> +			tdc_start_head_req(tdc);
> +
> +	raw_spin_unlock_irqrestore(&tdc->lock, flags);
> +}
> +
> +static void tegra_dma_reset_client(struct tegra_dma_channel *tdc)
> +{
> +	u32 csr = tdc_read(tdc, TEGRA_GPCDMA_CHAN_CSR);
> +
> +	csr &= ~(TEGRA_GPCDMA_CSR_REQ_SEL_MASK);
> +	csr |= TEGRA_GPCDMA_CSR_REQ_SEL_UNUSED;
> +	tdc_write(tdc, TEGRA_GPCDMA_CHAN_CSR, csr);
> +}
> +
> +static int tegra_dma_terminate_all(struct dma_chan *dc)
> +{
> +	struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> +	unsigned long wcount = 0;
> +	unsigned long status;
> +	unsigned long flags;
> +	bool was_busy;
> +	int err;
> +
> +	raw_spin_lock_irqsave(&tdc->lock, flags);
> +
> +	if (!tdc->dma_desc) {
> +		raw_spin_unlock_irqrestore(&tdc->lock, flags);
> +		return 0;
> +	}
> +
> +	if (!tdc->busy)
> +		goto skip_dma_stop;
> +
> +	if (tdc->tdma->chip_data->hw_support_pause) {
> +		err = tegra_dma_pause(tdc);
> +		if (err) {
> +			raw_spin_unlock_irqrestore(&tdc->lock, flags);
> +			return err;
> +		}
> +	} else {
> +		/* Before Reading DMA status to figure out number
> +		 * of bytes transferred by DMA channel:
> +		 * Change the client associated with the DMA channel
> +		 * to stop DMA engine from starting any more bursts for
> +		 * the given client and wait for in flight bursts to complete
> +		 */
> +		tegra_dma_reset_client(tdc);
> +
> +		/* Wait for in flight data transfer to finish */
> +		udelay(TEGRA_GPCDMA_BURST_COMPLETE_TIME);
> +
> +		/* If TX/RX path is still active wait till it becomes
> +		 * inactive
> +		 */
> +
> +		if (readl_relaxed_poll_timeout_atomic(tdc->tdma->base_addr +
> +				tdc->chan_base_offset +
> +				TEGRA_GPCDMA_CHAN_STATUS,
> +				status,
> +				!(status & (TEGRA_GPCDMA_STATUS_CHANNEL_TX |
> +				TEGRA_GPCDMA_STATUS_CHANNEL_RX)),
> +				5,
> +				TEGRA_GPCDMA_BURST_COMPLETION_TIMEOUT)) {
> +			dev_dbg(tdc2dev(tdc), "Timeout waiting for DMA burst completion!\n");
> +			tegra_dma_dump_chan_regs(tdc);
> +		}

I would be tempted to make the code in the 'else' clause 
tegra_dma_sw_pause(). Then you could have tegra_dma_hw_pause() and 
tegra_dma_sw_pause().

> +	}
> +
> +	status = tdc_read(tdc, TEGRA_GPCDMA_CHAN_STATUS);
> +	wcount = tdc_read(tdc, TEGRA_GPCDMA_CHAN_XFER_COUNT);
> +	if (status & TEGRA_GPCDMA_STATUS_ISE_EOC) {
> +		dev_dbg(tdc2dev(tdc), "%s():handling isr\n", __func__);
> +		tdc->isr_handler(tdc, true);
> +		status = tdc_read(tdc, TEGRA_GPCDMA_CHAN_STATUS);
> +		wcount = tdc_read(tdc, TEGRA_GPCDMA_CHAN_XFER_COUNT);
> +	}
> +
> +	was_busy = tdc->busy;
> +
> +	tegra_dma_stop(tdc);
> +	if (tdc->dma_desc && was_busy)
> +		tdc->dma_desc->bytes_transferred +=
> +			tdc->dma_desc->bytes_requested - (wcount * 4);
> +
> +skip_dma_stop:
> +	tegra_dma_abort_all(tdc);
> +	vchan_free_chan_resources(&tdc->vc);
> +	if (tdc->is_pending) {
> +		tdc->is_pending = false;
> +		kfree(tdc->dma_desc);
> +	}
> +
> +	raw_spin_unlock_irqrestore(&tdc->lock, flags);
> +	return 0;
> +}
> +
> +static enum dma_status tegra_dma_tx_status(struct dma_chan *dc,
> +					   dma_cookie_t cookie,
> +					   struct dma_tx_state *txstate)
> +{
> +	struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> +	struct tegra_dma_desc *dma_desc = NULL;
> +	struct virt_dma_desc *vd;
> +	unsigned int residual;
> +	enum dma_status ret;
> +	unsigned long flags;
> +
> +	raw_spin_lock_irqsave(&tdc->lock, flags);
> +
> +	ret = dma_cookie_status(dc, cookie, txstate);
> +	if (ret == DMA_COMPLETE) {
> +		raw_spin_unlock_irqrestore(&tdc->lock, flags);
> +		return ret;
> +	}
> +
> +	vd = vchan_find_desc(&tdc->vc, cookie);
> +	if (vd)
> +		dma_desc = vd_to_tegra_dma_desc(vd);
> +
> +	if (dma_desc) {
> +		residual =  dma_desc->bytes_requested -
> +					(dma_desc->bytes_transferred %
> +					dma_desc->bytes_requested);
> +		dma_set_residue(txstate, residual);
> +		kfree(dma_desc);
> +	} else {
> +		dev_err(tdc2dev(tdc), "cookie %d is not found\n", cookie);
> +	}
> +
> +	raw_spin_unlock_irqrestore(&tdc->lock, flags);
> +	return ret;
> +}
> +
> +static inline int get_bus_width(struct tegra_dma_channel *tdc,
> +				enum dma_slave_buswidth slave_bw)
> +{
> +	switch (slave_bw) {
> +	case DMA_SLAVE_BUSWIDTH_1_BYTE:
> +		return TEGRA_GPCDMA_MMIOSEQ_BUS_WIDTH_8;
> +	case DMA_SLAVE_BUSWIDTH_2_BYTES:
> +		return TEGRA_GPCDMA_MMIOSEQ_BUS_WIDTH_16;
> +	case DMA_SLAVE_BUSWIDTH_4_BYTES:
> +		return TEGRA_GPCDMA_MMIOSEQ_BUS_WIDTH_32;
> +	default:
> +		dev_err(tdc2dev(tdc), "given slave bw is not supported\n");
> +		return -EINVAL;
> +	}
> +}
> +
> +static inline int get_burst_size_by_len(int len)
> +{
> +	int ret;
> +
> +	switch (len) {
> +	case BIT(0) ... BIT(2):
> +		ret = TEGRA_GPCDMA_MMIOSEQ_BURST_1;
> +		break;
> +	case BIT(3):
> +		ret = TEGRA_GPCDMA_MMIOSEQ_BURST_2;
> +		break;
> +	case BIT(4):
> +		ret = TEGRA_GPCDMA_MMIOSEQ_BURST_4;
> +		break;
> +	case BIT(5):
> +		ret = TEGRA_GPCDMA_MMIOSEQ_BURST_8;
> +		break;
> +	default:
> +		ret = TEGRA_GPCDMA_MMIOSEQ_BURST_16;
> +		break;
> +	}
> +
> +	return ret;
> +}
> +
> +static inline int get_burst_size(struct tegra_dma_channel *tdc,
> +				 u32 burst_size,
> +				 enum dma_slave_buswidth slave_bw,
> +				 int len)
> +{
> +	int burst_mmio_width, burst_byte, ret;
> +
> +	/*
> +	 * burst_size from client is in terms of the bus_width.
> +	 * convert that into words.
> +	 */
> +	burst_byte = burst_size * slave_bw;
> +	burst_mmio_width = burst_byte / 4;
> +
> +	switch (burst_mmio_width) {
> +	case 0:
> +		ret = get_burst_size_by_len(len);
> +		break;
> +	case 1:
> +		ret = TEGRA_GPCDMA_MMIOSEQ_BURST_1;
> +		break;
> +	case 2 ... 3:
> +		ret = TEGRA_GPCDMA_MMIOSEQ_BURST_2;
> +		break;
> +	case 4 ... 7:
> +		ret = TEGRA_GPCDMA_MMIOSEQ_BURST_4;
> +		break;
> +	case 8 ... 15:
> +		ret = TEGRA_GPCDMA_MMIOSEQ_BURST_8;
> +		break;
> +	default:
> +		ret = TEGRA_GPCDMA_MMIOSEQ_BURST_16;
> +		break;
> +	}
> +
> +	return ret;
> +}
> +
> +static int get_transfer_param(struct tegra_dma_channel *tdc,
> +			      enum dma_transfer_direction direction,
> +				  unsigned long *apb_addr,
> +			      unsigned long *mmio_seq,
> +				  unsigned long *csr,
> +			      unsigned int *burst_size,
> +			      enum dma_slave_buswidth *slave_bw)
> +{
> +	switch (direction) {
> +	case DMA_MEM_TO_DEV:
> +		*apb_addr = tdc->dma_sconfig.dst_addr;
> +		*mmio_seq = get_bus_width(tdc, tdc->dma_sconfig.dst_addr_width);
> +		*burst_size = tdc->dma_sconfig.dst_maxburst;
> +		*slave_bw = tdc->dma_sconfig.dst_addr_width;
> +		*csr = TEGRA_GPCDMA_CSR_DMA_MEM2IO_FC;
> +		return 0;
> +
> +	case DMA_DEV_TO_MEM:
> +		*apb_addr = tdc->dma_sconfig.src_addr;
> +		*mmio_seq = get_bus_width(tdc, tdc->dma_sconfig.src_addr_width);
> +		*burst_size = tdc->dma_sconfig.src_maxburst;
> +		*slave_bw = tdc->dma_sconfig.src_addr_width;
> +		*csr = TEGRA_GPCDMA_CSR_DMA_IO2MEM_FC;
> +		return 0;
> +	case DMA_MEM_TO_MEM:
> +		*burst_size = tdc->dma_sconfig.src_addr_width;
> +		*csr = TEGRA_GPCDMA_CSR_DMA_MEM2MEM;
> +		return 0;
> +	default:
> +		dev_err(tdc2dev(tdc), "Dma direction is not supported\n");
> +		return -EINVAL;
> +	}
> +	return -EINVAL;
> +}
> +
> +static struct dma_async_tx_descriptor *
> +tegra_dma_prep_dma_memset(struct dma_chan *dc, dma_addr_t dest, int value,
> +			  size_t len, unsigned long flags)
> +{
> +	struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> +	struct tegra_dma_desc *dma_desc;
> +	unsigned long csr, mc_seq;
> +
> +	/* Set dma mode to fixed pattern */
> +	csr = TEGRA_GPCDMA_CSR_DMA_FIXED_PAT;
> +	/* Enable once or continuous mode */
> +	csr |= TEGRA_GPCDMA_CSR_ONCE;
> +	/* Enable IRQ mask */
> +	csr |= TEGRA_GPCDMA_CSR_IRQ_MASK;
> +	/* Enable the dma interrupt */
> +	if (flags & DMA_PREP_INTERRUPT)
> +		csr |= TEGRA_GPCDMA_CSR_IE_EOC;
> +	/* Configure default priority weight for the channel */
> +	csr |= FIELD_PREP(TEGRA_GPCDMA_CSR_WEIGHT, 1);
> +
> +	mc_seq =  tdc_read(tdc, TEGRA_GPCDMA_CHAN_MCSEQ);
> +	/* retain stream-id and clean rest */
> +	mc_seq &= TEGRA_GPCDMA_MCSEQ_STREAM_ID0_MASK;
> +
> +	/* Set the address wrapping */
> +	mc_seq |= FIELD_PREP(TEGRA_GPCDMA_MCSEQ_WRAP0,
> +						TEGRA_GPCDMA_MCSEQ_WRAP_NONE);
> +	mc_seq |= FIELD_PREP(TEGRA_GPCDMA_MCSEQ_WRAP1,
> +						TEGRA_GPCDMA_MCSEQ_WRAP_NONE);
> +
> +	/* Program outstanding MC requests */
> +	mc_seq |= FIELD_PREP(TEGRA_GPCDMA_MCSEQ_REQ_COUNT, 1);
> +	/* Set burst size */
> +	mc_seq |= TEGRA_GPCDMA_MCSEQ_BURST_16;
> +
> +	dma_desc = kzalloc(sizeof(*dma_desc), GFP_NOWAIT);
> +	if (!dma_desc)
> +		return NULL;
> +
> +	dma_desc->bytes_requested = 0;
> +	dma_desc->bytes_transferred = 0;
> +
> +	if ((len & 3) || (dest & 3) ||
> +	    len > tdc->tdma->chip_data->max_dma_count) {
> +		dev_err(tdc2dev(tdc),
> +			"Dma length/memory address is not supported\n");
> +		kfree(dma_desc);
> +		return NULL;
> +	}
> +
> +	dma_desc->bytes_requested += len;
> +	dma_desc->ch_regs.src_ptr = 0;
> +	dma_desc->ch_regs.dst_ptr = dest;
> +	dma_desc->ch_regs.high_addr_ptr =
> +			FIELD_PREP(TEGRA_GPCDMA_HIGH_ADDR_DST_PTR, (dest >> 32));
> +	dma_desc->ch_regs.fixed_pattern = value;
> +	/* Word count reg takes value as (N +1) words */
> +	dma_desc->ch_regs.wcount = ((len - 4) >> 2);
> +	dma_desc->ch_regs.csr = csr;
> +	dma_desc->ch_regs.mmio_seq = 0;
> +	dma_desc->ch_regs.mc_seq = mc_seq;
> +
> +	tdc->dma_desc = dma_desc;
> +
> +	if (!tdc->isr_handler)
> +		tdc->isr_handler = handle_once_dma_done;

Is this actually set to anything other than handle_once_dma_done? In not 
you can get rid of the function pointer completely.

> +
> +	return vchan_tx_prep(&tdc->vc, &dma_desc->vd, flags);
> +}
> +
> +static struct dma_async_tx_descriptor *
> +tegra_dma_prep_dma_memcpy(struct dma_chan *dc, dma_addr_t dest,
> +			  dma_addr_t src,	size_t len, unsigned long flags)
> +{
> +	struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> +	struct tegra_dma_desc *dma_desc;
> +	unsigned long csr, mc_seq;
> +
> +	/* Set dma mode to memory to memory transfer */
> +	csr = TEGRA_GPCDMA_CSR_DMA_MEM2MEM;
> +	/* Enable once or continuous mode */
> +	csr |= TEGRA_GPCDMA_CSR_ONCE;
> +	/* Enable IRQ mask */
> +	csr |= TEGRA_GPCDMA_CSR_IRQ_MASK;
> +	/* Enable the dma interrupt */
> +	if (flags & DMA_PREP_INTERRUPT)
> +		csr |= TEGRA_GPCDMA_CSR_IE_EOC;
> +	/* Configure default priority weight for the channel */
> +	csr |= FIELD_PREP(TEGRA_GPCDMA_CSR_WEIGHT, 1);
> +
> +	mc_seq =  tdc_read(tdc, TEGRA_GPCDMA_CHAN_MCSEQ);
> +	/* retain stream-id and clean rest */
> +	mc_seq &= (TEGRA_GPCDMA_MCSEQ_STREAM_ID0_MASK) |
> +				(TEGRA_GPCDMA_MCSEQ_STREAM_ID1_MASK);
> +
> +	/* Set the address wrapping */
> +	mc_seq |= FIELD_PREP(TEGRA_GPCDMA_MCSEQ_WRAP0,
> +						TEGRA_GPCDMA_MCSEQ_WRAP_NONE);
> +	mc_seq |= FIELD_PREP(TEGRA_GPCDMA_MCSEQ_WRAP1,
> +						TEGRA_GPCDMA_MCSEQ_WRAP_NONE);
> +
> +	/* Program outstanding MC requests */
> +	mc_seq |= FIELD_PREP(TEGRA_GPCDMA_MCSEQ_REQ_COUNT, 1);
> +	/* Set burst size */
> +	mc_seq |= TEGRA_GPCDMA_MCSEQ_BURST_16;
> +
> +	dma_desc = kzalloc(sizeof(*dma_desc), GFP_NOWAIT);
> +	if (!dma_desc)
> +		return NULL;
> +
> +	dma_desc->bytes_requested = 0;
> +	dma_desc->bytes_transferred = 0;
> +
> +	if ((len & 3) || (src & 3) || (dest & 3) ||
> +	    len > tdc->tdma->chip_data->max_dma_count) {
> +		dev_err(tdc2dev(tdc),
> +			"Dma length/memory address is not supported\n");
> +		kfree(dma_desc);
> +		return NULL;
> +	}
> +
> +	dma_desc->bytes_requested += len;
> +	dma_desc->ch_regs.src_ptr = src;
> +	dma_desc->ch_regs.dst_ptr = dest;
> +	dma_desc->ch_regs.high_addr_ptr =
> +		FIELD_PREP(TEGRA_GPCDMA_HIGH_ADDR_SRC_PTR, (src >> 32));
> +	dma_desc->ch_regs.high_addr_ptr |=
> +		FIELD_PREP(TEGRA_GPCDMA_HIGH_ADDR_DST_PTR, (dest >> 32));
> +	/* Word count reg takes value as (N +1) words */
> +	dma_desc->ch_regs.wcount = ((len - 4) >> 2);
> +	dma_desc->ch_regs.csr = csr;
> +	dma_desc->ch_regs.mmio_seq = 0;
> +	dma_desc->ch_regs.mc_seq = mc_seq;
> +
> +	if (!tdc->isr_handler)
> +		tdc->isr_handler = handle_once_dma_done;
> +
> +	return vchan_tx_prep(&tdc->vc, &dma_desc->vd, flags);
> +}
> +
> +static struct dma_async_tx_descriptor *
> +tegra_dma_prep_slave_sg(struct dma_chan *dc, struct scatterlist *sgl,
> +			unsigned int sg_len, enum dma_transfer_direction direction,
> +		unsigned long flags, void *context)
> +{
> +	struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> +	unsigned long csr, mc_seq, apb_ptr = 0, mmio_seq = 0;
> +	enum dma_slave_buswidth slave_bw;
> +	struct tegra_dma_desc *dma_desc;
> +	struct scatterlist *sg;
> +	u32 burst_size;
> +	unsigned int i;
> +	int ret;
> +
> +	if (!tdc->config_init) {
> +		dev_err(tdc2dev(tdc), "dma channel is not configured\n");
> +		return NULL;
> +	}
> +	if (sg_len < 1) {
> +		dev_err(tdc2dev(tdc), "Invalid segment length %d\n", sg_len);
> +		return NULL;
> +	}
> +
> +	ret = get_transfer_param(tdc, direction, &apb_ptr, &mmio_seq, &csr,
> +				 &burst_size, &slave_bw);
> +	if (ret < 0)
> +		return NULL;
> +
> +	/* Enable once or continuous mode */
> +	csr |= TEGRA_GPCDMA_CSR_ONCE;
> +	/* Program the slave id in requestor select */
> +	csr |= FIELD_PREP(TEGRA_GPCDMA_CSR_REQ_SEL_MASK, tdc->slave_id);
> +	/* Enable IRQ mask */
> +	csr |= TEGRA_GPCDMA_CSR_IRQ_MASK;
> +	/* Configure default priority weight for the channel*/
> +	csr |= FIELD_PREP(TEGRA_GPCDMA_CSR_WEIGHT, 1);
> +
> +	/* Enable the dma interrupt */
> +	if (flags & DMA_PREP_INTERRUPT)
> +		csr |= TEGRA_GPCDMA_CSR_IE_EOC;
> +
> +	mc_seq =  tdc_read(tdc, TEGRA_GPCDMA_CHAN_MCSEQ);
> +	/* retain stream-id and clean rest */
> +	mc_seq &= TEGRA_GPCDMA_MCSEQ_STREAM_ID0_MASK;
> +
> +	/* Set the address wrapping on both MC and MMIO side */
> +
> +	mc_seq |= FIELD_PREP(TEGRA_GPCDMA_MCSEQ_WRAP0,
> +							TEGRA_GPCDMA_MCSEQ_WRAP_NONE);
> +	mc_seq |= FIELD_PREP(TEGRA_GPCDMA_MCSEQ_WRAP1,
> +							TEGRA_GPCDMA_MCSEQ_WRAP_NONE);
> +	mmio_seq |= FIELD_PREP(TEGRA_GPCDMA_MMIOSEQ_WRAP_WORD, 1);
> +
> +	/* Program 2 MC outstanding requests by default. */
> +	mc_seq |= FIELD_PREP(TEGRA_GPCDMA_MCSEQ_REQ_COUNT, 1);
> +
> +	/* Setting MC burst size depending on MMIO burst size */
> +	if (burst_size == 64)
> +		mc_seq |= TEGRA_GPCDMA_MCSEQ_BURST_16;
> +	else
> +		mc_seq |= TEGRA_GPCDMA_MCSEQ_BURST_2;
> +
> +	dma_desc = kzalloc(sizeof(*dma_desc), GFP_NOWAIT);
> +	if (!dma_desc)
> +		return NULL;
> +
> +	dma_desc->bytes_requested = 0;
> +	dma_desc->bytes_transferred = 0;
> +
> +	/* Make transfer requests */
> +	for_each_sg(sgl, sg, sg_len, i) {
> +		u32 len;
> +		dma_addr_t mem;
> +
> +		mem = sg_dma_address(sg);
> +		len = sg_dma_len(sg);
> +
> +		if ((len & 3) || (mem & 3) ||
> +		    len > tdc->tdma->chip_data->max_dma_count) {
> +			dev_err(tdc2dev(tdc),
> +				"Dma length/memory address is not supported\n");
> +			kfree(dma_desc);
> +			return NULL;
> +		}
> +
> +		mmio_seq |= get_burst_size(tdc, burst_size, slave_bw, len);
> +		dma_desc->bytes_requested += len;
> +
> +		if (direction == DMA_MEM_TO_DEV) {
> +			dma_desc->ch_regs.src_ptr = mem;
> +			dma_desc->ch_regs.dst_ptr = apb_ptr;
> +			dma_desc->ch_regs.high_addr_ptr =
> +				FIELD_PREP(TEGRA_GPCDMA_HIGH_ADDR_SRC_PTR, (mem >> 32));
> +		} else if (direction == DMA_DEV_TO_MEM) {
> +			dma_desc->ch_regs.src_ptr = apb_ptr;
> +			dma_desc->ch_regs.dst_ptr = mem;
> +			dma_desc->ch_regs.high_addr_ptr =
> +				FIELD_PREP(TEGRA_GPCDMA_HIGH_ADDR_DST_PTR, (mem >> 32));
> +		}
> +
> +		/*
> +		 * Word count register takes input in words. Writing a value
> +		 * of N into word count register means a req of (N+1) words.
> +		 */
> +		dma_desc->ch_regs.wcount = ((len - 4) >> 2);
> +		dma_desc->ch_regs.csr = csr;
> +		dma_desc->ch_regs.mmio_seq = mmio_seq;
> +		dma_desc->ch_regs.mc_seq = mc_seq;
> +		tdc->dma_desc = dma_desc;
> +	}
> +
> +	/*
> +	 * Make sure that mode should not be conflicting with currently
> +	 * configured mode.
> +	 */
> +	if (!tdc->isr_handler)
> +		tdc->isr_handler = handle_once_dma_done;
> +
> +	return vchan_tx_prep(&tdc->vc, &dma_desc->vd, flags);
> +}
> +
> +static int tegra_dma_alloc_chan_resources(struct dma_chan *dc)
> +{
> +	struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> +
> +	dma_cookie_init(&tdc->vc.chan);
> +	tdc->config_init = false;
> +	return 0;
> +}
> +
> +static void tegra_dma_chan_synchronize(struct dma_chan *dc)
> +{
> +	struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> +
> +	vchan_synchronize(&tdc->vc);
> +}
> +
> +static void tegra_dma_free_chan_resources(struct dma_chan *dc)
> +{
> +	struct tegra_dma_channel *tdc = to_tegra_dma_chan(dc);
> +	unsigned long flags;
> +
> +	dev_dbg(tdc2dev(tdc), "Freeing channel %d\n", tdc->id);
> +
> +	if (tdc->busy)
> +		tegra_dma_terminate_all(dc);
> +
> +	tegra_dma_chan_synchronize(dc);
> +
> +	tasklet_kill(&tdc->vc.task);
> +	raw_spin_lock_irqsave(&tdc->lock, flags);
> +	tdc->config_init = false;
> +	tdc->isr_handler = NULL;
> +	tdc->slave_id = -1;
> +	raw_spin_unlock_irqrestore(&tdc->lock, flags);
> +}
> +
> +static struct dma_chan *tegra_dma_of_xlate(struct of_phandle_args *dma_spec,
> +					   struct of_dma *ofdma)
> +{
> +	struct tegra_dma *tdma = ofdma->of_dma_data;
> +	struct tegra_dma_channel *tdc;
> +	struct dma_chan *chan;
> +
> +	chan = dma_get_any_slave_channel(&tdma->dma_dev);
> +	if (!chan)
> +		return NULL;
> +
> +	tdc = to_tegra_dma_chan(chan);
> +	tdc->slave_id = dma_spec->args[0];
> +
> +	return chan;
> +}
> +
> +static const struct tegra_dma_chip_data tegra186_dma_chip_data = {
> +	.nr_channels = 31,
> +	.channel_reg_size = SZ_64K,
> +	.max_dma_count = SZ_1G,
> +	.hw_support_pause = false,
> +};
> +
> +static const struct tegra_dma_chip_data tegra194_dma_chip_data = {
> +	.nr_channels = 31,
> +	.channel_reg_size = SZ_64K,
> +	.max_dma_count = SZ_1G,
> +	.hw_support_pause = true,
> +};
> +
> +static const struct of_device_id tegra_dma_of_match[] = {
> +	{
> +		.compatible = "nvidia,tegra186-gpcdma",
> +		.data = &tegra186_dma_chip_data,
> +	}, {
> +		.compatible = "nvidia,tegra194-gpcdma",
> +		.data = &tegra194_dma_chip_data,
> +	}, {
> +	},
> +};
> +MODULE_DEVICE_TABLE(of, tegra_dma_of_match);
> +
> +static int tegra_dma_program_sid(struct tegra_dma_channel *tdc,
> +				 int chan, int stream_id)
> +{
> +	unsigned int reg_val =  tdc_read(tdc, TEGRA_GPCDMA_CHAN_MCSEQ);
> +
> +	reg_val &= ~(TEGRA_GPCDMA_MCSEQ_STREAM_ID0_MASK);
> +	reg_val &= ~(TEGRA_GPCDMA_MCSEQ_STREAM_ID1_MASK);
> +
> +	reg_val |= FIELD_PREP(TEGRA_GPCDMA_MCSEQ_STREAM_ID0_MASK, stream_id);
> +	reg_val |= FIELD_PREP(TEGRA_GPCDMA_MCSEQ_STREAM_ID1_MASK, stream_id);
> +
> +	tdc_write(tdc, TEGRA_GPCDMA_CHAN_MCSEQ, reg_val);
> +	return 0;
> +}
> +
> +static int tegra_dma_probe(struct platform_device *pdev)
> +{
> +	const struct tegra_dma_chip_data *cdata = NULL;
> +	const unsigned int start_chan_idx = 1;

What is this?

> +	unsigned int stream_id, i;
> +	struct tegra_dma *tdma;
> +	struct resource	*res;
> +	int ret;
> +
> +	cdata = of_device_get_match_data(&pdev->dev);
> +
> +	ret = of_property_read_u32(pdev->dev.of_node,
> +				   "nvidia,stream-id", &stream_id);

Property not mentioned in the binding doc.

> +	if (ret)
> +		stream_id = TEGRA186_SID_GPCDMA_0;
> +
> +	tdma = devm_kzalloc(&pdev->dev, sizeof(*tdma) + cdata->nr_channels *
> +			sizeof(struct tegra_dma_channel), GFP_KERNEL);
> +	if (!tdma)
> +		return -ENOMEM;
> +
> +	tdma->dev = &pdev->dev;
> +	tdma->chip_data = cdata;
> +	platform_set_drvdata(pdev, tdma);
> +
> +	tdma->base_addr = devm_platform_ioremap_resource(pdev, 0);
> +	if (IS_ERR(tdma->base_addr))
> +		return PTR_ERR(tdma->base_addr);
> +
> +	tdma->rst = devm_reset_control_get_exclusive(&pdev->dev, "gpcdma");
> +	if (IS_ERR(tdma->rst)) {
> +		if (!(PTR_ERR(tdma->rst) == -EPROBE_DEFER))
> +			dev_err(&pdev->dev, "Missing controller reset\n");

dev_err_probe()

> +		return PTR_ERR(tdma->rst);
> +	}
> +	reset_control_reset(tdma->rst);
> +
> +	tdma->dma_dev.dev = &pdev->dev;
> +
> +	INIT_LIST_HEAD(&tdma->dma_dev.channels);
> +	for (i = 0; i < cdata->nr_channels; i++) {
> +		struct tegra_dma_channel *tdc = &tdma->channels[i];
> +
> +		tdc->chan_base_offset = TEGRA_GPCDMA_CHANNEL_BASE_ADD_OFFSET +
> +					start_chan_idx * cdata->channel_reg_size +
> +					i * cdata->channel_reg_size;
> +		res = platform_get_resource(pdev, IORESOURCE_IRQ,
> +					    start_chan_idx + i);
> +		if (!res) {
> +			ret = -EINVAL;
> +			dev_err(&pdev->dev, "No irq resource for chan %d\n", i);
> +			goto err_irq;

Is this goto needed?

> +		}
> +		tdc->irq = res->start;
> +		snprintf(tdc->name, sizeof(tdc->name), "gpcdma.%d", i);
> +
> +		tdc->tdma = tdma;
> +		tdc->id = i;
> +		tdc->slave_id = -1;
> +
> +		vchan_init(&tdc->vc, &tdma->dma_dev);
> +		tdc->vc.desc_free = tegra_dma_desc_free;
> +		raw_spin_lock_init(&tdc->lock);
> +
> +		/* program stream-id for this channel */
> +		tegra_dma_program_sid(tdc, i, stream_id);
> +		tdc->stream_id = stream_id;
> +	}
> +
> +	dma_cap_set(DMA_SLAVE, tdma->dma_dev.cap_mask);
> +	dma_cap_set(DMA_PRIVATE, tdma->dma_dev.cap_mask);
> +	dma_cap_set(DMA_MEMCPY, tdma->dma_dev.cap_mask);
> +	dma_cap_set(DMA_MEMSET, tdma->dma_dev.cap_mask);
> +
> +	/*
> +	 * Only word aligned transfers are supported. Set the copy
> +	 * alignment shift.
> +	 */
> +	tdma->dma_dev.copy_align = 2;
> +	tdma->dma_dev.fill_align = 2;
> +	tdma->dma_dev.device_alloc_chan_resources =
> +					tegra_dma_alloc_chan_resources;
> +	tdma->dma_dev.device_free_chan_resources =
> +					tegra_dma_free_chan_resources;
> +	tdma->dma_dev.device_prep_slave_sg = tegra_dma_prep_slave_sg;
> +	tdma->dma_dev.device_prep_dma_memcpy = tegra_dma_prep_dma_memcpy;
> +	tdma->dma_dev.device_prep_dma_memset = tegra_dma_prep_dma_memset;
> +	tdma->dma_dev.device_config = tegra_dma_slave_config;
> +	tdma->dma_dev.device_terminate_all = tegra_dma_terminate_all;
> +	tdma->dma_dev.device_tx_status = tegra_dma_tx_status;
> +	tdma->dma_dev.device_issue_pending = tegra_dma_issue_pending;
> +	tdma->dma_dev.device_synchronize = tegra_dma_chan_synchronize;
> +	tdma->dma_dev.residue_granularity = DMA_RESIDUE_GRANULARITY_BURST;
> +
> +	/* Register DMA channel interrupt handlers after everything is setup */
> +	for (i = 0; i < cdata->nr_channels; i++) {
> +		struct tegra_dma_channel *tdc = &tdma->channels[i];
> +
> +		ret = devm_request_irq(&pdev->dev, tdc->irq,
> +				       tegra_dma_isr, 0, tdc->name, tdc);
> +		if (ret) {
> +			dev_err(&pdev->dev,
> +				"request_irq failed with err %d channel %d\n",
> +				i, ret);
> +			goto err_irq;
> +		}
> +	}
> +
> +	ret = dma_async_device_register(&tdma->dma_dev);
> +	if (ret < 0) {
> +		dev_err(&pdev->dev,
> +			"GPC DMA driver registration failed %d\n", ret);
> +		goto err_irq;
> +	}
> +
> +	ret = of_dma_controller_register(pdev->dev.of_node,
> +					 tegra_dma_of_xlate, tdma);
> +	if (ret < 0) {
> +		dev_err(&pdev->dev,
> +			"GPC DMA OF registration failed %d\n", ret);
> +		goto err_unregister_dma_dev;
> +	}
> +
> +	dev_info(&pdev->dev, "GPC DMA driver register %d channels\n",
> +		 cdata->nr_channels);
> +
> +	return 0;
> +
> +err_unregister_dma_dev:
> +	dma_async_device_unregister(&tdma->dma_dev);
> +err_irq:
> +	return ret;
> +}
> +
> +static int tegra_dma_remove(struct platform_device *pdev)
> +{
> +	struct tegra_dma *tdma = platform_get_drvdata(pdev);
> +
> +	of_dma_controller_free(pdev->dev.of_node);
> +	dma_async_device_unregister(&tdma->dma_dev);
> +
> +	return 0;
> +}
> +
> +/*
> + * Save and restore csr and channel register on pm_suspend
> + * and pm_resume respectively
> + */
> +static int __maybe_unused tegra_dma_pm_suspend(struct device *dev)
> +{
> +	struct tegra_dma *tdma = dev_get_drvdata(dev);
> +	unsigned long flags;
> +	unsigned int i;
> +	bool busy;
> +
> +	for (i = 0; i < tdma->chip_data->nr_channels; i++) {
> +		struct tegra_dma_channel *tdc = &tdma->channels[i];
> +
> +		raw_spin_lock_irqsave(&tdc->lock, flags);
> +		busy = tdc->busy;
> +		raw_spin_unlock_irqrestore(&tdc->lock, flags);
> +
> +		if (busy) {
> +			dev_err(tdma->dev, "channel %u busy\n", i);
> +			return -EBUSY;
> +		}
> +	}

Do we need to ensure that no one attempts to start the DMA after it has 
been suspended?

> +
> +	return 0;
> +}
> +
> +static int __maybe_unused tegra_dma_pm_resume(struct device *dev)
> +{
> +	struct tegra_dma *tdma = dev_get_drvdata(dev);
> +	unsigned int i;
> +
> +	reset_control_reset(tdma->rst);
> +
> +	for (i = 0; i < tdma->chip_data->nr_channels; i++) {
> +		struct tegra_dma_channel *tdc = &tdma->channels[i];
> +
> +		tegra_dma_program_sid(tdc, i, tdc->stream_id);
> +	}
> +
> +	return 0;
> +}
> +
> +static const struct __maybe_unused dev_pm_ops tegra_dma_dev_pm_ops = {
> +	SET_SYSTEM_SLEEP_PM_OPS(tegra_dma_pm_suspend, tegra_dma_pm_resume)
> +};
> +
> +static struct platform_driver tegra_dmac_driver = {
> +	.driver = {
> +		.name	= "tegra-gpcdma",
> +		.owner = THIS_MODULE,
> +		.pm	= &tegra_dma_dev_pm_ops,
> +		.of_match_table = tegra_dma_of_match,
> +	},
> +	.probe		= tegra_dma_probe,
> +	.remove		= tegra_dma_remove,
> +};
> +
> +module_platform_driver(tegra_dmac_driver);
> +
> +MODULE_ALIAS("platform:tegra-gpc-dma");
> +MODULE_DESCRIPTION("NVIDIA Tegra GPC DMA Controller driver");
> +MODULE_AUTHOR("Pavan Kunapuli <pkunapuli@nvidia.com>");
> +MODULE_AUTHOR("Rajesh Gumasta <rgumasta@nvidia.com>");
> +MODULE_LICENSE("GPL v2");
>