linux-kernel - Re: [PATCH v3] media: mtk-vpu: Ensure alignment of 8 for DTCM buffer

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Message-ID: <c1712278-8d18-2958-853b-09e5097ddce7@xs4all.nl>
Date:   Wed, 1 Sep 2021 10:50:13 +0200
From:   Hans Verkuil <hverkuil@...all.nl>
To:     Dafna Hirschfeld <dafna.hirschfeld@...labora.com>,
        linux-media@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Cc:     Alexandre Courbot <acourbot@...omium.org>, kernel@...labora.com,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        dafna3@...il.com, mchehab@...nel.org, tfiga@...omium.org,
        minghsiu.tsai@...iatek.com, houlong.wei@...iatek.com,
        andrew-ct.chen@...iatek.com, tiffany.lin@...iatek.com,
        matthias.bgg@...il.com, courbot@...omium.org, hsinyi@...omium.org,
        eizan@...omium.org
Subject: Re: [PATCH v3] media: mtk-vpu: Ensure alignment of 8 for DTCM buffer

On 25/08/2021 12:17, Dafna Hirschfeld wrote:
> From: Alexandre Courbot <acourbot@...omium.org>
> 
> When running memcpy_toio:
> memcpy_toio(send_obj->share_buf, buf, len);
> it was found that errors appear if len is not a multiple of 8:
> 
> [58.350841] mtk-mdp 14001000.rdma: processing failed: -22
> 
> This patch ensures the copy of a multile of 8 size by calling

multile -> multiple

> round_up(len, 8) when copying
> 
> Fixes: e6599adfad30 ("media: mtk-vpu: avoid unaligned access to DTCM buffer.")
> Signed-off-by: Alexandre Courbot <acourbot@...omium.org>
> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@...labora.com>
> Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@...labora.com>
> ---
> changes since v2:
> 1. do the extra copy only if len is not multiple of 8
> 
> changes since v1:
> 1. change sign-off-by tags
> 2. change values to memset
> 
>  drivers/media/platform/mtk-vpu/mtk_vpu.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/platform/mtk-vpu/mtk_vpu.c b/drivers/media/platform/mtk-vpu/mtk_vpu.c
> index ec290dde59cf..658161ee3e4e 100644
> --- a/drivers/media/platform/mtk-vpu/mtk_vpu.c
> +++ b/drivers/media/platform/mtk-vpu/mtk_vpu.c
> @@ -349,7 +349,16 @@ int vpu_ipi_send(struct platform_device *pdev,
>  		}
>  	} while (vpu_cfg_readl(vpu, HOST_TO_VPU));
>  
> -	memcpy_toio(send_obj->share_buf, buf, len);
> +	if (len % 8 != 0) {

You need to add a comment here explaining why this is done (basically what
you also say in the commit log).

Otherwise people would have to dig into the git log to figure out why this
code is the way it is.

Is len often not a multiple of 8? If that's the case, then it might be easier
to just always do the memset/memcpy.

Regards,

	Hans

> +		unsigned char data[SHARE_BUF_SIZE];
> +
> +		memset(data + len, 0, sizeof(data) - len);
> +		memcpy(data, buf, len);
> +		memcpy_toio(send_obj->share_buf, data, round_up(len, 8));
> +	} else {
> +		memcpy_toio(send_obj->share_buf, buf, len);
> +	}
> +
>  	writel(len, &send_obj->len);
>  	writel(id, &send_obj->id);
>  
>