linux-kernel - Re: [PATCH v5 4/7] dmaengine: xilinx_dma: program hardware supported buffer length

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Message-ID: <20180918162508.GD2613@vkoul-mobl>
Date:   Tue, 18 Sep 2018 09:25:08 -0700
From:   Vinod <vkoul@...nel.org>
To:     Andrea Merello <andrea.merello@...il.com>
Cc:     dan.j.williams@...el.com, michal.simek@...inx.com,
        appana.durga.rao@...inx.com, dmaengine@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        robh+dt@...nel.org, mark.rutland@....com,
        devicetree@...r.kernel.org, radhey.shyam.pandey@...inx.com
Subject: Re: [PATCH v5 4/7] dmaengine: xilinx_dma: program hardware supported
 buffer length

On 07-09-18, 08:24, Andrea Merello wrote:
> From: Radhey Shyam Pandey <radhey.shyam.pandey@...inx.com>
> 
> AXI-DMA IP supports configurable (c_sg_length_width) buffer length
> register width, hence read buffer length (xlnx,sg-length-width) DT
> property and ensure that driver doesn't program buffer length
> exceeding the supported limit. For VDMA and CDMA there is no change.
> 
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: devicetree@...r.kernel.org
> Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@...inx.com>
> Signed-off-by: Michal Simek <michal.simek@...inx.com>
> Signed-off-by: Andrea Merello <andrea.merello@...il.com> [rebase, reword]
> ---
> Changes in v2:
>         - drop original patch and replace with the one in Xilinx tree
> Changes in v3:
> 	- cc DT maintainers/ML
> Changes in v4:
> 	- upper bound for the property should be 26, not 23
> 	- add warn for width > 23 as per xilinx original patch
> 	- rework due to changes introduced in 1/6
> Changes in v5:
> 	None
> ---
>  drivers/dma/xilinx/xilinx_dma.c | 36 +++++++++++++++++++++++++--------
>  1 file changed, 28 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
> index aaa6de8a70e4..b17f24e4ec35 100644
> --- a/drivers/dma/xilinx/xilinx_dma.c
> +++ b/drivers/dma/xilinx/xilinx_dma.c
> @@ -158,7 +158,9 @@
>  #define XILINX_DMA_REG_BTT		0x28
>  
>  /* AXI DMA Specific Masks/Bit fields */
> -#define XILINX_DMA_MAX_TRANS_LEN	GENMASK(22, 0)
> +#define XILINX_DMA_MAX_TRANS_LEN_MIN	8
> +#define XILINX_DMA_MAX_TRANS_LEN_MAX	23
> +#define XILINX_DMA_V2_MAX_TRANS_LEN_MAX	26
>  #define XILINX_DMA_CR_COALESCE_MAX	GENMASK(23, 16)
>  #define XILINX_DMA_CR_CYCLIC_BD_EN_MASK	BIT(4)
>  #define XILINX_DMA_CR_COALESCE_SHIFT	16
> @@ -418,6 +420,7 @@ struct xilinx_dma_config {
>   * @rxs_clk: DMA s2mm stream clock
>   * @nr_channels: Number of channels DMA device supports
>   * @chan_id: DMA channel identifier
> + * @max_buffer_len: Max buffer length
>   */
>  struct xilinx_dma_device {
>  	void __iomem *regs;
> @@ -437,6 +440,7 @@ struct xilinx_dma_device {
>  	struct clk *rxs_clk;
>  	u32 nr_channels;
>  	u32 chan_id;
> +	u32 max_buffer_len;
>  };
>  
>  /* Macros */
> @@ -964,7 +968,7 @@ static int xilinx_dma_calc_copysize(struct xilinx_dma_chan *chan,
>  				    int size, int done)
>  {
>  	size_t copy = min_t(size_t, size - done,
> -		     XILINX_DMA_MAX_TRANS_LEN);
> +			    chan->xdev->max_buffer_len);

hmm why not add max_buffer_len in patch 1 again, and then use default
len as XILINX_DMA_MAX_TRANS_LEN and add multiple lengths here :)

- 
~Vinod