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Date:   Mon, 27 Aug 2018 11:04:09 +0530
From:   Vinod <vkoul@kernel.org>
To:     Andrea Merello <andrea.merello@gmail.com>
Cc:     dan.j.williams@intel.com, michal.simek@xilinx.com,
        appana.durga.rao@xilinx.com, dmaengine@vger.kernel.org,
        v4-000linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, robh+dt@kernel.org,
        mark.rutland@arm.com, devicetree@vger.kernel.org,
        radhey.shyam.pandey@xilinx.com
Subject: Re: [PATCH v4 5/7] dmaengine: xilinx_dma: autodetect whether the HW
 supports scatter-gather
Message-ID: <20180827053409.GV2388@vkoul-mobl>
References: <20180802141012.19970-1-andrea.merello@gmail.com>
 <20180802141012.19970-5-andrea.merello@gmail.com>
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On 02-08-18, 16:10, Andrea Merello wrote:
> The AXIDMA and CDMA HW can be either direct-access or scatter-gather
> version. These are SW incompatible.
> 
> The driver can handle both versions: a DT property was used to
> tell the driver whether to assume the HW is in scatter-gather mode.
> 
> This patch makes the driver to autodetect this information. The DT
> property is not required anymore.
> 
> No changes for VDMA.
> 
> Cc: Rob Herring <robh+dt@kernel.org>
> Cc: Mark Rutland <mark.rutland@arm.com>
> Cc: devicetree@vger.kernel.org
> Cc: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
> Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
> Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
> ---
> Changes in v2:
> 	- autodetect only in !VDMA case
> Changes in v3:
> 	- cc DT maintainers/ML
> Changes in v4:
> 	- fix typos in commit message
> ---
>  drivers/dma/xilinx/xilinx_dma.c | 14 ++++++++++----

So you are not removing this property from binding document? Or are
there variants which dont have hw mechanism?

>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
> index b17f24e4ec35..78d0f2f8225e 100644
> --- a/drivers/dma/xilinx/xilinx_dma.c
> +++ b/drivers/dma/xilinx/xilinx_dma.c
> @@ -86,6 +86,7 @@
>  #define XILINX_DMA_DMASR_DMA_DEC_ERR		BIT(6)
>  #define XILINX_DMA_DMASR_DMA_SLAVE_ERR		BIT(5)
>  #define XILINX_DMA_DMASR_DMA_INT_ERR		BIT(4)
> +#define XILINX_DMA_DMASR_SG_MASK		BIT(3)
>  #define XILINX_DMA_DMASR_IDLE			BIT(1)
>  #define XILINX_DMA_DMASR_HALTED		BIT(0)
>  #define XILINX_DMA_DMASR_DELAY_MASK		GENMASK(31, 24)
> @@ -407,7 +408,6 @@ struct xilinx_dma_config {
>   * @dev: Device Structure
>   * @common: DMA device structure
>   * @chan: Driver specific DMA channel
> - * @has_sg: Specifies whether Scatter-Gather is present or not
>   * @mcdma: Specifies whether Multi-Channel is present or not
>   * @flush_on_fsync: Flush on frame sync
>   * @ext_addr: Indicates 64 bit addressing is supported by dma device
> @@ -427,7 +427,6 @@ struct xilinx_dma_device {
>  	struct device *dev;
>  	struct dma_device common;
>  	struct xilinx_dma_chan *chan[XILINX_DMA_MAX_CHANS_PER_DEVICE];
> -	bool has_sg;
>  	bool mcdma;
>  	u32 flush_on_fsync;
>  	bool ext_addr;
> @@ -2400,7 +2399,6 @@ static int xilinx_dma_chan_probe(struct xilinx_dma_device *xdev,
>  
>  	chan->dev = xdev->dev;
>  	chan->xdev = xdev;
> -	chan->has_sg = xdev->has_sg;
>  	chan->desc_pendingcount = 0x0;
>  	chan->ext_addr = xdev->ext_addr;
>  	/* This variable ensures that descriptors are not
> @@ -2493,6 +2491,15 @@ static int xilinx_dma_chan_probe(struct xilinx_dma_device *xdev,
>  		chan->stop_transfer = xilinx_dma_stop_transfer;
>  	}
>  
> +	/* check if SG is enabled (only for AXIDMA and CDMA) */
> +	if (xdev->dma_config->dmatype != XDMA_TYPE_VDMA) {
> +		if (dma_ctrl_read(chan, XILINX_DMA_REG_DMASR) &
> +		    XILINX_DMA_DMASR_SG_MASK)
> +			chan->has_sg = true;
> +		dev_dbg(chan->dev, "ch %d: SG %s\n", chan->id,
> +			chan->has_sg ? "enabled" : "disabled");
> +	}
> +
>  	/* Initialize the tasklet */
>  	tasklet_init(&chan->tasklet, xilinx_dma_do_tasklet,
>  			(unsigned long)chan);
> @@ -2631,7 +2638,6 @@ static int xilinx_dma_probe(struct platform_device *pdev)
>  		return PTR_ERR(xdev->regs);
>  
>  	/* Retrieve the DMA engine properties from the device tree */
> -	xdev->has_sg = of_property_read_bool(node, "xlnx,include-sg");
>  	xdev->max_buffer_len = GENMASK(XILINX_DMA_MAX_TRANS_LEN_MAX - 1, 0);
>  
>  	if (xdev->dma_config->dmatype == XDMA_TYPE_AXIDMA) {
> -- 
> 2.17.1

-- 
~Vinod