linux-kernel - Re: [PATCH] media: platform: mtk-mdp: Fix mdp_ipi

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Date:   Thu, 21 Apr 2022 13:03:02 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     minghsiu.tsai@...iatek.com
Cc:     houlong.wei@...iatek.com, andrew-ct.chen@...iatek.com,
        mchehab@...nel.org, matthias.bgg@...il.com, hans.verkuil@...co.com,
        linux-media@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com, acourbot@...omium.org, irui.wang@...iatek.com
Subject: Re: [PATCH] media: platform: mtk-mdp: Fix mdp_ipi_comm structure
 alignment

Il 07/03/22 16:56, AngeloGioacchino Del Regno ha scritto:
> The mdp_ipi_comm structure defines a command that is either
> PROCESS (start processing) or DEINIT (destroy instance); we
> are using this one to send PROCESS or DEINIT commands from Linux
> to an MDP instance through a VPU write but, while the first wants
> us to stay 4-bytes aligned, the VPU instead requires an 8-bytes
> data alignment.
> 
> Keeping in mind that these commands are executed immediately
> after sending them (hence not chained with others before the
> VPU/MDP "actually" start executing), it is fine to simply add
> a padding of 4 bytes to this structure: this keeps the same
> performance as before, as we're still stack-allocating it,
> while avoiding hackery inside of mtk-vpu to ensure alignment
> bringing a definitely bigger performance impact.
> 
> Fixes: c8eb2d7e8202 ("[media] media: Add Mediatek MDP Driver")
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>

Hello,
is there any issue with this patch?

Regards,
Angelo

> ---
> 
> This patch has been tested on Acer Chromebook R 13 (MT8173 Elm) on Debian Sid.
> 
> This is an alternative solution to the mtk-vpu approach, found here:
> https://lore.kernel.org/all/20210920170408.1561-1-dafna.hirschfeld@collabora.com
> 
>   drivers/media/platform/mtk-mdp/mtk_mdp_ipi.h | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/media/platform/mtk-mdp/mtk_mdp_ipi.h b/drivers/media/platform/mtk-mdp/mtk_mdp_ipi.h
> index 2cb8cecb3077..b810c96695c8 100644
> --- a/drivers/media/platform/mtk-mdp/mtk_mdp_ipi.h
> +++ b/drivers/media/platform/mtk-mdp/mtk_mdp_ipi.h
> @@ -40,12 +40,14 @@ struct mdp_ipi_init {
>    * @ipi_id        : IPI_MDP
>    * @ap_inst       : AP mtk_mdp_vpu address
>    * @vpu_inst_addr : VPU MDP instance address
> + * @padding       : Alignment padding
>    */
>   struct mdp_ipi_comm {
>   	uint32_t msg_id;
>   	uint32_t ipi_id;
>   	uint64_t ap_inst;
>   	uint32_t vpu_inst_addr;
> +	uint32_t padding;
>   };
>   
>   /**


-- 
AngeloGioacchino Del Regno
Software Engineer

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