linux-kernel - Re: [PATCH] fpga: zynqmp: Make word align the configuration data

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Date:   Sat, 18 Mar 2023 17:25:24 +0800
From:   Xu Yilun <yilun.xu@...el.com>
To:     Nava kishore Manne <nava.kishore.manne@....com>
Cc:     mdf@...nel.org, hao.wu@...el.com, trix@...hat.com,
        michal.simek@...inx.com, linux-fpga@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fpga: zynqmp: Make word align the configuration data

On 2023-03-14 at 15:12:22 +0530, Nava kishore Manne wrote:
> To avoid unwanted copies at firmware(PMUFW) this patch provides a fix

The copy happens in firmware? Please help briefly describe the firmware
operations in commit message.

> to align programmable logic(PL) configuration data if the data is not
> word-aligned. To align the configuration data this patch adds a few
> padding bytes and these additional padding bytes will not create any
> functional impact on the PL configuration.
> 
> Signed-off-by: Nava kishore Manne <nava.kishore.manne@....com>
> ---
>  drivers/fpga/zynqmp-fpga.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/fpga/zynqmp-fpga.c b/drivers/fpga/zynqmp-fpga.c
> index c60f20949c47..70a12dc6e15c 100644
> --- a/drivers/fpga/zynqmp-fpga.c
> +++ b/drivers/fpga/zynqmp-fpga.c
> @@ -15,6 +15,9 @@
>  /* Constant Definitions */
>  #define IXR_FPGA_DONE_MASK	BIT(3)
>  
> +#define DUMMY_PAD_BYTE		0xFF
> +#define FPGA_WORD_SIZE		4
> +
>  /**
>   * struct zynqmp_fpga_priv - Private data structure
>   * @dev:	Device data structure
> @@ -41,18 +44,26 @@ static int zynqmp_fpga_ops_write(struct fpga_manager *mgr,
>  				 const char *buf, size_t size)
>  {
>  	struct zynqmp_fpga_priv *priv;
> +	int word_align, ret, index;
>  	dma_addr_t dma_addr;
>  	u32 eemi_flags = 0;
>  	char *kbuf;
> -	int ret;
>  
>  	priv = mgr->priv;
> +	word_align = size % FPGA_WORD_SIZE;
> +	if (word_align)
> +		word_align = FPGA_WORD_SIZE - word_align;
> +
> +	size = size + word_align;

Does the Macro ALIGN() help?

>  
>  	kbuf = dma_alloc_coherent(priv->dev, size, &dma_addr, GFP_KERNEL);
>  	if (!kbuf)
>  		return -ENOMEM;
>  
> -	memcpy(kbuf, buf, size);

This is historical, but why do the realloc & copy? Any better way?

> +	for (index = 0; index < word_align; index++)
> +		kbuf[index] = DUMMY_PAD_BYTE;
> +
> +	memcpy(&kbuf[index], buf, size - index);

Generally I object to massive copy in fpga_manager_ops::write if not
necessary. If there is an alignment requirement from HW, it should be
noticed to the caller in some way, before the buffer is created.

Thanks,
Yilun

>  
>  	wmb(); /* ensure all writes are done before initiate FW call */
>  
> -- 
> 2.25.1
>