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Subject: Re: [RFC PATCH 2/2] spi: spi-mem: Add support for Zynq QSPI
 controller
To:     Naga Sureshkumar Relli <naga.sureshkumar.relli@xilinx.com>,
        <broonie@kernel.org>, <bbrezillon@kernel.org>
CC:     <linux-spi@vger.kernel.org>, <dwmw2@infradead.org>,
        <marek.vasut@gmail.com>, <richard@nod.at>,
        <linux-mtd@lists.infradead.org>, <linux-kernel@vger.kernel.org>,
        <michal.simek@xilinx.com>, <nagasuresh12@gmail.com>
References: <1551337361-11665-1-git-send-email-naga.sureshkumar.relli@xilinx.com>
From:   Vignesh Raghavendra <vigneshr@ti.com>
Message-ID: <48dafcc4-1b9d-9ce2-9228-78e73252781f@ti.com>
Date:   Fri, 1 Mar 2019 15:41:39 +0530
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On 28/02/19 12:32 PM, Naga Sureshkumar Relli wrote:
> Add support for QSPI controller driver used by Xilinx Zynq SOC.
> 
> Signed-off-by: Naga Sureshkumar Relli <naga.sureshkumar.relli@xilinx.com>
> ---
>  drivers/spi/Kconfig         |   8 +
>  drivers/spi/Makefile        |   1 +
>  drivers/spi/spi-zynq-qspi.c | 780 ++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 789 insertions(+)
>  create mode 100644 drivers/spi/spi-zynq-qspi.c
> 
> diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
> index 9f89cb1..f12c880 100644
> --- a/drivers/spi/Kconfig
> +++ b/drivers/spi/Kconfig
> @@ -816,6 +816,14 @@ config SPI_XTENSA_XTFPGA
>  	  16 bit words in SPI mode 0, automatically asserting CS on transfer
>  	  start and deasserting on end.
>  
> +config SPI_ZYNQ_QSPI
> +	tristate "Xilinx Zynq QSPI controller"
> +	depends on ARCH_ZYNQ
> +	help
> +	  This enables support for the Zynq Quad SPI controller
> +	  in master mode.
> +	  This controller only supports SPI memory interface.
> +
>  config SPI_ZYNQMP_GQSPI
>  	tristate "Xilinx ZynqMP GQSPI controller"
>  	depends on SPI_MASTER && HAS_DMA
> diff --git a/drivers/spi/Makefile b/drivers/spi/Makefile
> index f296270..565db4d 100644
> --- a/drivers/spi/Makefile
> +++ b/drivers/spi/Makefile
> @@ -115,6 +115,7 @@ obj-$(CONFIG_SPI_XCOMM)		+= spi-xcomm.o
>  obj-$(CONFIG_SPI_XILINX)		+= spi-xilinx.o
>  obj-$(CONFIG_SPI_XLP)			+= spi-xlp.o
>  obj-$(CONFIG_SPI_XTENSA_XTFPGA)		+= spi-xtensa-xtfpga.o
> +obj-$(CONFIG_SPI_ZYNQ_QSPI)		+= spi-zynq-qspi.o
>  obj-$(CONFIG_SPI_ZYNQMP_GQSPI)		+= spi-zynqmp-gqspi.o
>  
>  # SPI slave protocol handlers
> diff --git a/drivers/spi/spi-zynq-qspi.c b/drivers/spi/spi-zynq-qspi.c
> new file mode 100644
> index 0000000..87c9ec2
> --- /dev/null
> +++ b/drivers/spi/spi-zynq-qspi.c
> @@ -0,0 +1,780 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Copyright (C) 2019 Xilinx, Inc.
> + *
> + * Author: Naga Sureshkumar Relli <nagasure@xilinx.com>
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/delay.h>
> +#include <linux/gpio.h>
> +#include <linux/interrupt.h>
> +#include <linux/io.h>
> +#include <linux/module.h>
> +#include <linux/of_irq.h>
> +#include <linux/of_address.h>
> +#include <linux/platform_device.h>
> +#include <linux/spi/spi.h>
> +#include <linux/workqueue.h>
> +#include <linux/spi/spi-mem.h>
> +
> +/* Register offset definitions */
> +#define ZYNQ_QSPI_CONFIG_OFFSET		0x00 /* Configuration  Register, RW */
> +#define ZYNQ_QSPI_STATUS_OFFSET		0x04 /* Interrupt Status Register, RO */
> +#define ZYNQ_QSPI_IEN_OFFSET		0x08 /* Interrupt Enable Register, WO */
> +#define ZYNQ_QSPI_IDIS_OFFSET		0x0C /* Interrupt Disable Reg, WO */
> +#define ZYNQ_QSPI_IMASK_OFFSET		0x10 /* Interrupt Enabled Mask Reg,RO */
> +#define ZYNQ_QSPI_ENABLE_OFFSET		0x14 /* Enable/Disable Register, RW */
> +#define ZYNQ_QSPI_DELAY_OFFSET		0x18 /* Delay Register, RW */
> +#define ZYNQ_QSPI_TXD_00_00_OFFSET	0x1C /* Transmit 4-byte inst, WO */
> +#define ZYNQ_QSPI_TXD_00_01_OFFSET	0x80 /* Transmit 1-byte inst, WO */
> +#define ZYNQ_QSPI_TXD_00_10_OFFSET	0x84 /* Transmit 2-byte inst, WO */
> +#define ZYNQ_QSPI_TXD_00_11_OFFSET	0x88 /* Transmit 3-byte inst, WO */
> +#define ZYNQ_QSPI_RXD_OFFSET		0x20 /* Data Receive Register, RO */
> +#define ZYNQ_QSPI_SIC_OFFSET		0x24 /* Slave Idle Count Register, RW */
> +#define ZYNQ_QSPI_TX_THRESH_OFFSET	0x28 /* TX FIFO Watermark Reg, RW */
> +#define ZYNQ_QSPI_RX_THRESH_OFFSET	0x2C /* RX FIFO Watermark Reg, RW */
> +#define ZYNQ_QSPI_GPIO_OFFSET		0x30 /* GPIO Register, RW */
> +#define ZYNQ_QSPI_LINEAR_CFG_OFFSET	0xA0 /* Linear Adapter Config Ref, RW */
> +#define ZYNQ_QSPI_MOD_ID_OFFSET		0xFC /* Module ID Register, RO */
> +
> +/*
> + * QSPI Configuration Register bit Masks
> + *
> + * This register contains various control bits that effect the operation
> + * of the QSPI controller
> + */
> +#define ZYNQ_QSPI_CONFIG_IFMODE_MASK	0x80000000 /* Flash Memory Interface */
> +#define ZYNQ_QSPI_CONFIG_MANSRT_MASK	0x00010000 /* Manual TX Start */
> +#define ZYNQ_QSPI_CONFIG_MANSRTEN_MASK	0x00008000 /* Enable Manual TX Mode */
> +#define ZYNQ_QSPI_CONFIG_SSFORCE_MASK	0x00004000 /* Manual Chip Select */
> +#define ZYNQ_QSPI_CONFIG_BDRATE_MASK	0x00000038 /* Baud Rate Divisor Mask */
> +#define ZYNQ_QSPI_CONFIG_CPHA_MASK	0x00000004 /* Clock Phase Control */
> +#define ZYNQ_QSPI_CONFIG_CPOL_MASK	0x00000002 /* Clock Polarity Control */
> +#define ZYNQ_QSPI_CONFIG_SSCTRL_MASK	0x00000400 /* Slave Select Mask */
> +#define ZYNQ_QSPI_CONFIG_FWIDTH_MASK	0x000000C0 /* FIFO width */
> +#define ZYNQ_QSPI_CONFIG_MSTREN_MASK	0x00000001 /* Master Mode */
> +

Convert to GENMASK() and BIT() macros

> +/*
> + * QSPI Configuration Register - Baud rate and slave select
> + *
> + * These are the values used in the calculation of baud rate divisor and
> + * setting the slave select.
> + */
> +#define ZYNQ_QSPI_BAUD_DIV_MAX		7 /* Baud rate divisor maximum */
> +#define ZYNQ_QSPI_BAUD_DIV_SHIFT	3 /* Baud rate divisor shift in CR */
> +#define ZYNQ_QSPI_SS_SHIFT		10 /* Slave Select field shift in CR */
> +
> +/*
> + * QSPI Interrupt Registers bit Masks
> + *
> + * All the four interrupt registers (Status/Mask/Enable/Disable) have the same
> + * bit definitions.
> + */
> +#define ZYNQ_QSPI_IXR_RX_OVERFLOW_MASK	0x00000001 /* QSPI RX FIFO Overflow */
> +#define ZYNQ_QSPI_IXR_TXNFULL_MASK	0x00000004 /* QSPI TX FIFO Overflow */
> +#define ZYNQ_QSPI_IXR_TXFULL_MASK	0x00000008 /* QSPI TX FIFO is full */
> +#define ZYNQ_QSPI_IXR_RXNEMTY_MASK	0x00000010 /* QSPI RX FIFO Not Empty */
> +#define ZYNQ_QSPI_IXR_RXF_FULL_MASK	0x00000020 /* QSPI RX FIFO is full */
> +#define ZYNQ_QSPI_IXR_TXF_UNDRFLOW_MASK	0x00000040 /* QSPI TX FIFO Underflow */
> +#define ZYNQ_QSPI_IXR_ALL_MASK		(ZYNQ_QSPI_IXR_RX_OVERFLOW_MASK | \
> +					ZYNQ_QSPI_IXR_TXNFULL_MASK | \
> +					ZYNQ_QSPI_IXR_TXFULL_MASK | \
> +					ZYNQ_QSPI_IXR_RXNEMTY_MASK | \
> +					ZYNQ_QSPI_IXR_RXF_FULL_MASK | \
> +					ZYNQ_QSPI_IXR_TXF_UNDRFLOW_MASK)
> +#define ZYNQ_QSPI_IXR_RXTX_MASK		(ZYNQ_QSPI_IXR_TXNFULL_MASK | \
> +					ZYNQ_QSPI_IXR_RXNEMTY_MASK)
> +

Convert to GENMASK() and BIT() macros

> +/*
> + * QSPI Enable Register bit Masks
> + *
> + * This register is used to enable or disable the QSPI controller
> + */
> +#define ZYNQ_QSPI_ENABLE_ENABLE_MASK	0x00000001 /* QSPI Enable Bit Mask */
> +
> +/*
> + * QSPI Linear Configuration Register
> + *
> + * It is named Linear Configuration but it controls other modes when not in
> + * linear mode also.
> + */
> +#define ZYNQ_QSPI_LCFG_TWO_MEM_MASK	0x40000000 /* LQSPI Two memories Mask */
> +#define ZYNQ_QSPI_LCFG_SEP_BUS_MASK	0x20000000 /* LQSPI Separate bus Mask */
> +#define ZYNQ_QSPI_LCFG_U_PAGE_MASK	0x10000000 /* LQSPI Upper Page Mask */
> +

Convert to GENMASK() and BIT() macros

> +#define ZYNQ_QSPI_LCFG_DUMMY_SHIFT	8
> +
> +#define ZYNQ_QSPI_FAST_READ_QOUT_CODE	0x6B /* read instruction code */
> +#define ZYNQ_QSPI_FIFO_DEPTH		63 /* FIFO depth in words */
> +#define ZYNQ_QSPI_RX_THRESHOLD		32 /* Rx FIFO threshold level */
> +#define ZYNQ_QSPI_TX_THRESHOLD		1 /* Tx FIFO threshold level */
> +
> +/*
> + * The modebits configurable by the driver to make the SPI support different
> + * data formats
> + */
> +#define MODEBITS			(SPI_CPOL | SPI_CPHA)
> +

Rename as ZYNQ_QSPI_MODEBITS to avoid namespace conflicts

> +/* Default number of chip selects */
> +#define ZYNQ_QSPI_DEFAULT_NUM_CS	1
> +
> +/**
> + * struct zynq_qspi - Defines qspi driver instance
> + * @regs:		Virtual address of the QSPI controller registers
> + * @refclk:		Pointer to the peripheral clock
> + * @pclk:		Pointer to the APB clock
> + * @irq:		IRQ number
> + * @txbuf:		Pointer to the TX buffer
> + * @rxbuf:		Pointer to the RX buffer
> + * @tx_bytes:		Number of bytes left to transfer
> + * @rx_bytes:		Number of bytes left to receive
> + * @data_completion:	completion structure
> + */
> +struct zynq_qspi {
> +	struct device *dev;
> +	void __iomem *regs;
> +	struct clk *refclk;
> +	struct clk *pclk;
> +	int irq;
> +	u8 *txbuf;
> +	u8 *rxbuf;
> +	int tx_bytes;
> +	int rx_bytes;
> +	struct completion data_completion;
> +};
> +
> +/*
> + * Inline functions for the QSPI controller read/write
> + */
> +static inline u32 zynq_qspi_read(struct zynq_qspi *xqspi, u32 offset)
> +{
> +	return readl_relaxed(xqspi->regs + offset);
> +}
> +
> +static inline void zynq_qspi_write(struct zynq_qspi *xqspi, u32 offset,
> +				   u32 val)
> +{
> +	writel_relaxed(val, xqspi->regs + offset);
> +}
> +
> +/**
> + * zynq_qspi_init_hw - Initialize the hardware
> + * @xqspi:	Pointer to the zynq_qspi structure
> + *
> + * The default settings of the QSPI controller's configurable parameters on
> + * reset are
> + *	- Master mode
> + *	- Baud rate divisor is set to 2
> + *	- Tx threshold set to 1l Rx threshold set to 32
> + *	- Flash memory interface mode enabled
> + *	- Size of the word to be transferred as 8 bit
> + * This function performs the following actions
> + *	- Disable and clear all the interrupts
> + *	- Enable manual slave select
> + *	- Enable manual start
> + *	- Deselect all the chip select lines
> + *	- Set the size of the word to be transferred as 32 bit
> + *	- Set the little endian mode of TX FIFO and
> + *	- Enable the QSPI controller
> + */
> +static void zynq_qspi_init_hw(struct zynq_qspi *xqspi)
> +{
> +	u32 config_reg;
> +
> +	zynq_qspi_write(xqspi, ZYNQ_QSPI_ENABLE_OFFSET, 0);
> +	zynq_qspi_write(xqspi, ZYNQ_QSPI_IDIS_OFFSET, ZYNQ_QSPI_IXR_ALL_MASK);
> +
> +	/* Disable linear mode as the boot loader may have used it */
> +	zynq_qspi_write(xqspi, ZYNQ_QSPI_LINEAR_CFG_OFFSET, 0);
> +
> +	/* Clear the RX FIFO */
> +	while (zynq_qspi_read(xqspi, ZYNQ_QSPI_STATUS_OFFSET) &
> +			      ZYNQ_QSPI_IXR_RXNEMTY_MASK)
> +		zynq_qspi_read(xqspi, ZYNQ_QSPI_RXD_OFFSET);
> +
> +	zynq_qspi_write(xqspi, ZYNQ_QSPI_STATUS_OFFSET, ZYNQ_QSPI_IXR_ALL_MASK);
> +	config_reg = zynq_qspi_read(xqspi, ZYNQ_QSPI_CONFIG_OFFSET);
> +	config_reg &= ~(ZYNQ_QSPI_CONFIG_MSTREN_MASK |
> +			ZYNQ_QSPI_CONFIG_CPOL_MASK |
> +			ZYNQ_QSPI_CONFIG_CPHA_MASK |
> +			ZYNQ_QSPI_CONFIG_BDRATE_MASK |
> +			ZYNQ_QSPI_CONFIG_SSFORCE_MASK |
> +			ZYNQ_QSPI_CONFIG_MANSRTEN_MASK |
> +			ZYNQ_QSPI_CONFIG_MANSRT_MASK);
> +	config_reg |= (ZYNQ_QSPI_CONFIG_MSTREN_MASK |
> +		       ZYNQ_QSPI_CONFIG_SSFORCE_MASK |
> +		       ZYNQ_QSPI_CONFIG_FWIDTH_MASK |
> +		       ZYNQ_QSPI_CONFIG_IFMODE_MASK);
> +	zynq_qspi_write(xqspi, ZYNQ_QSPI_CONFIG_OFFSET, config_reg);
> +
> +	zynq_qspi_write(xqspi, ZYNQ_QSPI_RX_THRESH_OFFSET,
> +			ZYNQ_QSPI_RX_THRESHOLD);
> +	zynq_qspi_write(xqspi, ZYNQ_QSPI_TX_THRESH_OFFSET,
> +			ZYNQ_QSPI_TX_THRESHOLD);
> +
> +	zynq_qspi_write(xqspi, ZYNQ_QSPI_ENABLE_OFFSET,
> +			ZYNQ_QSPI_ENABLE_ENABLE_MASK);
> +}
> +
> +static int zynq_qspi_check_buswidth(u8 width)
> +{
> +	switch (width) {
> +	case 1:
> +	case 2:
> +	case 4:
> +		return 0;
> +	}
> +
> +	return -ENOTSUPP;
> +}
> +
> +static bool zynq_qspi_supports_op(struct spi_mem *mem,
> +				  const struct spi_mem_op *op)
> +{
> +	int ret;
> +
> +	ret = zynq_qspi_check_buswidth(op->cmd.buswidth);
> +
> +	if (op->addr.nbytes)
> +		ret |= zynq_qspi_check_buswidth(op->addr.buswidth);
> +
> +	if (op->dummy.nbytes)
> +		ret |= zynq_qspi_check_buswidth(op->dummy.buswidth);
> +
> +	if (op->data.nbytes)
> +		ret |= zynq_qspi_check_buswidth(op->data.buswidth);
> +
> +	if (ret)
> +		return false;
> +

spi_mem_default_supports_op() already has this code.
Could you change, spi_mem_supports_op() to call
spi_mem_default_supports_op() first before controller specific
->supports_op()? So that, above code can be dropped.

> +	/*
> +	 * The number of address bytes should be equal to or less than 3 bytes.
> +	 */
> +	if (op->addr.nbytes > 3)
> +		return false;
> +

Hmm, how does the driver handle flash devices >16MB in size? Not supported?

> +	return true;
> +}
> +
> +/**
> + * zynq_qspi_rxfifo_op - Read 1..4 bytes from RxFIFO to RX buffer
> + * @xqspi:	Pointer to the zynq_qspi structure
> + * @size:	Number of bytes to be read (1..4)
> + */
> +static void zynq_qspi_rxfifo_op(struct zynq_qspi *xqspi, unsigned int size)
> +{
> +	u32 data;
> +
> +	data = zynq_qspi_read(xqspi, ZYNQ_QSPI_RXD_OFFSET);
> +
> +	if (xqspi->rxbuf) {
> +		memcpy(xqspi->rxbuf, ((u8 *)&data) + 4 - size, size);
> +		xqspi->rxbuf += size;
> +	}
> +
> +	xqspi->rx_bytes -= size;
> +	if (xqspi->rx_bytes < 0)
> +		xqspi->rx_bytes = 0;
> +}
> +
> +/**
> + * zynq_qspi_txfifo_op - Write 1..4 bytes from TX buffer to TxFIFO
> + * @xqspi:	Pointer to the zynq_qspi structure
> + * @size:	Number of bytes to be written (1..4)
> + */
> +static void zynq_qspi_txfifo_op(struct zynq_qspi *xqspi, unsigned int size)
> +{
> +	static const unsigned int offset[4] = {
> +		ZYNQ_QSPI_TXD_00_01_OFFSET, ZYNQ_QSPI_TXD_00_10_OFFSET,
> +		ZYNQ_QSPI_TXD_00_11_OFFSET, ZYNQ_QSPI_TXD_00_00_OFFSET };
> +	u32 data;
> +
> +	if (xqspi->txbuf) {
> +		data = 0xffffffff;
> +		memcpy(&data, xqspi->txbuf, size);
> +		xqspi->txbuf += size;
> +	} else {
> +		data = 0;
> +	}
> +
> +	xqspi->tx_bytes -= size;
> +	zynq_qspi_write(xqspi, offset[size - 1], data);
> +}
> +
> +/**
> + * zynq_qspi_chipselect - Select or deselect the chip select line
> + * @spi:	Pointer to the spi_device structure
> + * @assert:	1 for select or 0 for deselect the chip select line
> + */
> +static void zynq_qspi_chipselect(struct spi_device *spi, bool assert)
> +{
> +	struct spi_controller *ctrl = spi->master;
> +	struct zynq_qspi *xqspi = spi_controller_get_devdata(ctrl);
> +	u32 config_reg;
> +
> +	config_reg = zynq_qspi_read(xqspi, ZYNQ_QSPI_CONFIG_OFFSET);
> +	if (assert) {
> +		/* Select the slave */
> +		config_reg &= ~ZYNQ_QSPI_CONFIG_SSCTRL_MASK;
> +		config_reg |= (((~(BIT(spi->chip_select))) <<
> +				ZYNQ_QSPI_SS_SHIFT) &
> +				ZYNQ_QSPI_CONFIG_SSCTRL_MASK);
> +	} else {
> +		config_reg |= ZYNQ_QSPI_CONFIG_SSCTRL_MASK;
> +	}
> +
> +	zynq_qspi_write(xqspi, ZYNQ_QSPI_CONFIG_OFFSET, config_reg);
> +}
> +
> +/**
> + * zynq_qspi_config_op - Configure QSPI controller for specified transfer
> + * @xqspi:	Pointer to the zynq_qspi structure
> + * @qspi:	Pointer to the spi_device structure
> + *
> + * Sets the operational mode of QSPI controller for the next QSPI transfer and
> + * sets the requested clock frequency.
> + *
> + * Return:	0 on success and -EINVAL on invalid input parameter
> + *
> + * Note: If the requested frequency is not an exact match with what can be
> + * obtained using the prescalar value, the driver sets the clock frequency which
> + * is lower than the requested frequency (maximum lower) for the transfer. If
> + * the requested frequency is higher or lower than that is supported by the QSPI
> + * controller the driver will set the highest or lowest frequency supported by
> + * controller.
> + */
> +static int zynq_qspi_config_op(struct zynq_qspi *xqspi, struct spi_device *spi)
> +{
> +	u32 config_reg, baud_rate_val = 0;
> +
> +	/* Set the clock frequency */
> +	while ((baud_rate_val < ZYNQ_QSPI_BAUD_DIV_MAX)  &&
> +	       (clk_get_rate(xqspi->refclk) / (2 << baud_rate_val)) >
> +		spi->max_speed_hz)
> +		baud_rate_val++;

This can be simplified by using DIV_ROUND_UP() to find baud_rate_val


Regards
Vignesh

> +	config_reg = zynq_qspi_read(xqspi, ZYNQ_QSPI_CONFIG_OFFSET);
> +
> +	/* Set the QSPI clock phase and clock polarity */
> +	config_reg &= (~ZYNQ_QSPI_CONFIG_CPHA_MASK) &
> +		      (~ZYNQ_QSPI_CONFIG_CPOL_MASK);
> +	if (spi->mode & SPI_CPHA)
> +		config_reg |= ZYNQ_QSPI_CONFIG_CPHA_MASK;
> +	if (spi->mode & SPI_CPOL)
> +		config_reg |= ZYNQ_QSPI_CONFIG_CPOL_MASK;
> +
> +	config_reg &= ~ZYNQ_QSPI_CONFIG_BDRATE_MASK;
> +	config_reg |= (baud_rate_val << ZYNQ_QSPI_BAUD_DIV_SHIFT);
> +	zynq_qspi_write(xqspi, ZYNQ_QSPI_CONFIG_OFFSET, config_reg);
> +
> +	return 0;
> +}
> +
> +/**
> + * zynq_qspi_setup - Configure the QSPI controller
> + * @spi:	Pointer to the spi_device structure
> + *
> + * Sets the operational mode of QSPI controller for the next QSPI transfer, baud
> + * rate and divisor value to setup the requested qspi clock.
> + *
> + * Return:	0 on success and error value on failure
> + */
> +static int zynq_qspi_setup_op(struct spi_device *spi)
> +{
> +	struct spi_controller *ctrl = spi->master;
> +	struct zynq_qspi *qspi = spi_controller_get_devdata(ctrl);
> +
> +	if (ctrl->busy)
> +		return -EBUSY;
> +
> +	clk_enable(qspi->refclk);
> +	clk_enable(qspi->pclk);
> +	zynq_qspi_write(qspi, ZYNQ_QSPI_ENABLE_OFFSET,
> +			ZYNQ_QSPI_ENABLE_ENABLE_MASK);
> +
> +	return 0;
> +}
> +
> +/**
> + * zynq_qspi_write_op - Fills the TX FIFO with as many bytes as possible
> + * @xqspi:	Pointer to the zynq_qspi structure
> + * @txcount:	Maximum number of words to write
> + * @txempty:	Indicates that TxFIFO is empty
> + */
> +static void zynq_qspi_write_op(struct zynq_qspi *xqspi, int txcount,
> +			       bool txempty)
> +{
> +	int count, len, k;
> +
> +	len = xqspi->tx_bytes;
> +	if (len && len < 4) {
> +		/*
> +		 * We must empty the TxFIFO between accesses to TXD0,
> +		 * TXD1, TXD2, TXD3.
> +		 */
> +		if (txempty)
> +			zynq_qspi_txfifo_op(xqspi, len);
> +
> +		return;
> +	}
> +
> +	count = len / 4;
> +	if (count > txcount)
> +		count = txcount;
> +
> +	if (xqspi->txbuf) {
> +		writesl(xqspi->regs + ZYNQ_QSPI_TXD_00_00_OFFSET,
> +			xqspi->txbuf, count);
> +		xqspi->txbuf += count * 4;
> +	} else {
> +		for (k = 0; k < count; k++)
> +			writel_relaxed(0, xqspi->regs +
> +					  ZYNQ_QSPI_TXD_00_00_OFFSET);
> +	}
> +
> +	xqspi->tx_bytes -= count * 4;
> +}
> +
> +/**
> + * zynq_qspi_read_op - Drains the RX FIFO by as many bytes as possible
> + * @xqspi:	Pointer to the zynq_qspi structure
> + * @rxcount:	Maximum number of words to read
> + */
> +static void zynq_qspi_read_op(struct zynq_qspi *xqspi, int rxcount)
> +{
> +	int count, len, k;
> +
> +	len = xqspi->rx_bytes - xqspi->tx_bytes;
> +	count = len / 4;
> +	if (count > rxcount)
> +		count = rxcount;
> +	if (xqspi->rxbuf) {
> +		readsl(xqspi->regs + ZYNQ_QSPI_RXD_OFFSET,
> +		       xqspi->rxbuf, count);
> +		xqspi->rxbuf += count * 4;
> +	} else {
> +		for (k = 0; k < count; k++)
> +			readl_relaxed(xqspi->regs + ZYNQ_QSPI_RXD_OFFSET);
> +	}
> +	xqspi->rx_bytes -= count * 4;
> +	len -= count * 4;
> +
> +	if (len && len < 4 && count < rxcount)
> +		zynq_qspi_rxfifo_op(xqspi, len);
> +}
> +
> +/**
> + * zynq_qspi_irq - Interrupt service routine of the QSPI controller
> + * @irq:	IRQ number
> + * @dev_id:	Pointer to the xqspi structure
> + *
> + * This function handles TX empty only.
> + * On TX empty interrupt this function reads the received data from RX FIFO and
> + * fills the TX FIFO if there is any data remaining to be transferred.
> + *
> + * Return:	IRQ_HANDLED when interrupt is handled; IRQ_NONE otherwise.
> + */
> +static irqreturn_t zynq_qspi_irq(int irq, void *dev_id)
> +{
> +	u32 intr_status;
> +	bool txempty;
> +	struct zynq_qspi *xqspi = (struct zynq_qspi *)dev_id;
> +
> +	intr_status = zynq_qspi_read(xqspi, ZYNQ_QSPI_STATUS_OFFSET);
> +	zynq_qspi_write(xqspi, ZYNQ_QSPI_STATUS_OFFSET, intr_status);
> +
> +	if ((intr_status & ZYNQ_QSPI_IXR_TXNFULL_MASK) ||
> +	    (intr_status & ZYNQ_QSPI_IXR_RXNEMTY_MASK)) {
> +		/*
> +		 * This bit is set when Tx FIFO has < THRESHOLD entries.
> +		 * We have the THRESHOLD value set to 1,
> +		 * so this bit indicates Tx FIFO is empty.
> +		 */
> +		txempty = !!(intr_status & ZYNQ_QSPI_IXR_TXNFULL_MASK);
> +		/* Read out the data from the RX FIFO */
> +		zynq_qspi_read_op(xqspi, ZYNQ_QSPI_RX_THRESHOLD);
> +		if (xqspi->tx_bytes) {
> +			/* There is more data to send */
> +			zynq_qspi_write_op(xqspi, ZYNQ_QSPI_RX_THRESHOLD,
> +					   txempty);
> +		} else {
> +			/*
> +			 * If transfer and receive is completed then only send
> +			 * complete signal.
> +			 */
> +			if (!xqspi->rx_bytes) {
> +				zynq_qspi_write(xqspi,
> +						ZYNQ_QSPI_IDIS_OFFSET,
> +						ZYNQ_QSPI_IXR_RXTX_MASK);
> +				complete(&xqspi->data_completion);
> +			}
> +		}
> +		return IRQ_HANDLED;
> +	}
> +
> +	return IRQ_NONE;
> +}
> +
> +/**
> + * zynq_qspi_exec_mem_op() - Initiates the QSPI transfer
> + * @mem: the SPI memory
> + * @op: the memory operation to execute
> + *
> + * Executes a memory operation.
> + *
> + * This function first selects the chip and starts the memory operation.
> + *
> + * Return: 0 in case of success, a negative error code otherwise.
> + */
> +static int zynq_qspi_exec_mem_op(struct spi_mem *mem,
> +				 const struct spi_mem_op *op)
> +{
> +	struct zynq_qspi *xqspi = spi_controller_get_devdata(mem->spi->master);
> +	int err = 0, i;
> +	u8 *tmpbuf;
> +
> +	dev_dbg(xqspi->dev, "cmd:%#x mode:%d.%d.%d.%d\n",
> +		op->cmd.opcode, op->cmd.buswidth, op->addr.buswidth,
> +		op->dummy.buswidth, op->data.buswidth);
> +
> +	zynq_qspi_chipselect(mem->spi, true);
> +	zynq_qspi_config_op(xqspi, mem->spi);
> +
> +	if (op->cmd.opcode) {
> +		reinit_completion(&xqspi->data_completion);
> +		xqspi->txbuf = (u8 *)&op->cmd.opcode;
> +		xqspi->rxbuf = NULL;
> +		xqspi->tx_bytes = sizeof(op->cmd.opcode);
> +		xqspi->rx_bytes = sizeof(op->cmd.opcode);
> +		zynq_qspi_write_op(xqspi, ZYNQ_QSPI_FIFO_DEPTH, true);
> +		zynq_qspi_write(xqspi, ZYNQ_QSPI_IEN_OFFSET,
> +				ZYNQ_QSPI_IXR_RXTX_MASK);
> +		if (!wait_for_completion_interruptible_timeout(&xqspi->data_completion,
> +							       msecs_to_jiffies(1000))) {
> +			err = -ETIMEDOUT;
> +		}
> +	}
> +	zynq_qspi_config_op(xqspi, mem->spi);
> +	if (op->addr.nbytes) {
> +		for (i = 0; i < op->addr.nbytes; i++) {
> +			xqspi->txbuf[i] = op->addr.val >>
> +					(8 * (op->addr.nbytes - i - 1));
> +		}
> +
> +		reinit_completion(&xqspi->data_completion);
> +		xqspi->rxbuf = NULL;
> +		xqspi->tx_bytes = op->addr.nbytes;
> +		xqspi->rx_bytes = op->addr.nbytes;
> +		zynq_qspi_write_op(xqspi, ZYNQ_QSPI_FIFO_DEPTH, true);
> +		zynq_qspi_write(xqspi, ZYNQ_QSPI_IEN_OFFSET,
> +				ZYNQ_QSPI_IXR_RXTX_MASK);
> +		if (!wait_for_completion_interruptible_timeout(&xqspi->data_completion,
> +							       msecs_to_jiffies(1000))) {
> +			err = -ETIMEDOUT;
> +		}
> +	}
> +	zynq_qspi_config_op(xqspi, mem->spi);
> +	if (op->dummy.nbytes) {
> +		tmpbuf = kzalloc(op->dummy.nbytes, GFP_KERNEL);
> +		memset(tmpbuf, 0xff, op->dummy.nbytes);
> +		reinit_completion(&xqspi->data_completion);
> +		xqspi->txbuf = tmpbuf;
> +		xqspi->rxbuf = NULL;
> +		xqspi->tx_bytes = op->dummy.nbytes;
> +		xqspi->rx_bytes = op->dummy.nbytes;
> +		zynq_qspi_write_op(xqspi, ZYNQ_QSPI_FIFO_DEPTH, true);
> +		zynq_qspi_write(xqspi, ZYNQ_QSPI_IEN_OFFSET,
> +				ZYNQ_QSPI_IXR_RXTX_MASK);
> +		if (!wait_for_completion_interruptible_timeout(&xqspi->data_completion,
> +							       msecs_to_jiffies(1000))) {
> +			err = -ETIMEDOUT;
> +		}
> +		kfree(tmpbuf);
> +	}
> +	zynq_qspi_config_op(xqspi, mem->spi);
> +	if (op->data.nbytes) {
> +		reinit_completion(&xqspi->data_completion);
> +		if (op->data.dir == SPI_MEM_DATA_OUT) {
> +			xqspi->txbuf = (u8 *)op->data.buf.out;
> +			xqspi->tx_bytes = op->data.nbytes;
> +			xqspi->rxbuf = NULL;
> +			xqspi->rx_bytes = op->data.nbytes;
> +		} else {
> +			xqspi->txbuf = NULL;
> +			xqspi->rxbuf = (u8 *)op->data.buf.in;
> +			xqspi->rx_bytes = op->data.nbytes;
> +			xqspi->tx_bytes = op->data.nbytes;
> +		}
> +
> +		zynq_qspi_write_op(xqspi, ZYNQ_QSPI_FIFO_DEPTH, true);
> +		zynq_qspi_write(xqspi, ZYNQ_QSPI_IEN_OFFSET,
> +				ZYNQ_QSPI_IXR_RXTX_MASK);
> +		if (!wait_for_completion_interruptible_timeout(&xqspi->data_completion,
> +							       msecs_to_jiffies(1000))) {
> +			err = -ETIMEDOUT;
> +		}
> +	}
> +	zynq_qspi_chipselect(mem->spi, false);
> +
> +	return err;
> +}
> +
> +static const struct spi_controller_mem_ops zynq_qspi_mem_ops = {
> +	.supports_op = zynq_qspi_supports_op,
> +	.exec_op = zynq_qspi_exec_mem_op,
> +};
> +
> +/**
> + * zynq_qspi_probe - Probe method for the QSPI driver
> + * @pdev:	Pointer to the platform_device structure
> + *
> + * This function initializes the driver data structures and the hardware.
> + *
> + * Return:	0 on success and error value on failure
> + */
> +static int zynq_qspi_probe(struct platform_device *pdev)
> +{
> +	int ret = 0;
> +	struct spi_controller *ctlr;
> +	struct device *dev = &pdev->dev;
> +	struct device_node *np = dev->of_node;
> +	struct zynq_qspi *xqspi;
> +	struct resource *res;
> +	u32 num_cs;
> +
> +	ctlr = spi_alloc_master(&pdev->dev, sizeof(*xqspi));
> +	if (!ctlr)
> +		return -ENOMEM;
> +
> +	xqspi = spi_controller_get_devdata(ctlr);
> +	xqspi->dev = dev;
> +	platform_set_drvdata(pdev, xqspi);
> +	ctlr->mem_ops = &zynq_qspi_mem_ops;
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	xqspi->regs = devm_ioremap_resource(&pdev->dev, res);
> +	if (IS_ERR(xqspi->regs)) {
> +		ret = PTR_ERR(xqspi->regs);
> +		goto remove_master;
> +	}
> +
> +	xqspi->pclk = devm_clk_get(&pdev->dev, "pclk");
> +	if (IS_ERR(xqspi->pclk)) {
> +		dev_err(&pdev->dev, "pclk clock not found.\n");
> +		ret = PTR_ERR(xqspi->pclk);
> +		goto remove_master;
> +	}
> +
> +	init_completion(&xqspi->data_completion);
> +
> +	xqspi->refclk = devm_clk_get(&pdev->dev, "ref_clk");
> +	if (IS_ERR(xqspi->refclk)) {
> +		dev_err(&pdev->dev, "ref_clk clock not found.\n");
> +		ret = PTR_ERR(xqspi->refclk);
> +		goto remove_master;
> +	}
> +
> +	ret = clk_prepare_enable(xqspi->pclk);
> +	if (ret) {
> +		dev_err(&pdev->dev, "Unable to enable APB clock.\n");
> +		goto remove_master;
> +	}
> +
> +	ret = clk_prepare_enable(xqspi->refclk);
> +	if (ret) {
> +		dev_err(&pdev->dev, "Unable to enable device clock.\n");
> +		goto clk_dis_pclk;
> +	}
> +
> +	/* QSPI controller initializations */
> +	zynq_qspi_init_hw(xqspi);
> +
> +	xqspi->irq = platform_get_irq(pdev, 0);
> +	if (xqspi->irq <= 0) {
> +		ret = -ENXIO;
> +		dev_err(&pdev->dev, "irq resource not found\n");
> +		goto remove_master;
> +	}
> +	ret = devm_request_irq(&pdev->dev, xqspi->irq, zynq_qspi_irq,
> +			       0, pdev->name, xqspi);
> +	if (ret != 0) {
> +		ret = -ENXIO;
> +		dev_err(&pdev->dev, "request_irq failed\n");
> +		goto remove_master;
> +	}
> +
> +	ret = of_property_read_u32(pdev->dev.of_node, "num-cs",
> +				   &num_cs);
> +	if (ret < 0)
> +		ctlr->num_chipselect = ZYNQ_QSPI_DEFAULT_NUM_CS;
> +	else
> +		ctlr->num_chipselect = num_cs;
> +	ctlr->mode_bits =  SPI_RX_DUAL | SPI_RX_QUAD |
> +			    SPI_TX_DUAL | SPI_TX_QUAD;
> +	ctlr->mem_ops = &zynq_qspi_mem_ops;
> +	ctlr->setup = zynq_qspi_setup_op;
> +	ctlr->max_speed_hz = clk_get_rate(xqspi->refclk) / 2;
> +	ctlr->dev.of_node = np;
> +	ret = spi_register_controller(ctlr);
> +	if (ret) {
> +		dev_err(&pdev->dev, "spi_register_master failed\n");
> +		goto clk_dis_all;
> +	}
> +
> +	return ret;
> +
> +clk_dis_all:
> +	clk_disable_unprepare(xqspi->refclk);
> +clk_dis_pclk:
> +	clk_disable_unprepare(xqspi->pclk);
> +remove_master:
> +	spi_controller_put(ctlr);
> +
> +	return ret;
> +}
> +
> +/**
> + * zynq_qspi_remove - Remove method for the QSPI driver
> + * @pdev:	Pointer to the platform_device structure
> + *
> + * This function is called if a device is physically removed from the system or
> + * if the driver module is being unloaded. It frees all resources allocated to
> + * the device.
> + *
> + * Return:	0 on success and error value on failure
> + */
> +static int zynq_qspi_remove(struct platform_device *pdev)
> +{
> +	struct zynq_qspi *xqspi = platform_get_drvdata(pdev);
> +
> +	zynq_qspi_write(xqspi, ZYNQ_QSPI_ENABLE_OFFSET, 0);
> +
> +	clk_disable_unprepare(xqspi->refclk);
> +	clk_disable_unprepare(xqspi->pclk);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id zynq_qspi_of_match[] = {
> +	{ .compatible = "xlnx,zynq-qspi-1.0", },
> +	{ /* end of table */ }
> +};
> +
> +MODULE_DEVICE_TABLE(of, zynq_qspi_of_match);
> +
> +/*
> + * zynq_qspi_driver - This structure defines the QSPI platform driver
> + */
> +static struct platform_driver zynq_qspi_driver = {
> +	.probe = zynq_qspi_probe,
> +	.remove = zynq_qspi_remove,
> +	.driver = {
> +		.name = "zynq-qspi",
> +		.of_match_table = zynq_qspi_of_match,
> +	},
> +};
> +
> +module_platform_driver(zynq_qspi_driver);
> +
> +MODULE_AUTHOR("Xilinx, Inc.");
> +MODULE_DESCRIPTION("Xilinx Zynq QSPI driver");
> +MODULE_LICENSE("GPL");
>