Re: [PATCH] media: rkvdec: Add required padding

[Nicolas Dufresne <nicolas@ndufresne.ca>]

Le jeudi 27 octobre 2022 à 10:02 +0200, Andrzej Pietrasiewicz a écrit :
> The addresses of two elements of the segmap[][] member are passed to the
> hardware which expects 128-bit aligned addresses. However, without this
> patch offsetof(struct rkvdec_vp9_priv_tbl, segmap[0]) is an odd number
> (2421) but the hardware just ignores the 5 least significant bits of the
> address. As a result, the hardware writes the segmentation map to incorrect
> locations.
> 
> Inserting 11 bytes of padding corrects this situation by making the said
> addresses divisible by 16 (i.e. aligned on a 128-bit boundary).
> 
> Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@collabora.com>

Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>

For backport purposes, perhaps add ?

Fixes: f25709c4ff15 ("media: rkvdec: Add the VP9 backend")	

> ---
>  drivers/staging/media/rkvdec/rkvdec-vp9.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/staging/media/rkvdec/rkvdec-vp9.c b/drivers/staging/media/rkvdec/rkvdec-vp9.c
> index d8c1c0db15c7..cfae99b40ccb 100644
> --- a/drivers/staging/media/rkvdec/rkvdec-vp9.c
> +++ b/drivers/staging/media/rkvdec/rkvdec-vp9.c
> @@ -84,6 +84,8 @@ struct rkvdec_vp9_probs {
>  		struct rkvdec_vp9_inter_frame_probs inter;
>  		struct rkvdec_vp9_intra_only_frame_probs intra_only;
>  	};
> +	/* 128 bit alignment */
> +	u8 padding1[11];
>  };
>  
>  /* Data structure describing auxiliary buffer format. */
> @@ -1006,6 +1008,7 @@ static int rkvdec_vp9_start(struct rkvdec_ctx *ctx)
>  
>  	ctx->priv = vp9_ctx;
>  
> +	BUILD_BUG_ON(sizeof(priv_tbl->probs) % 16); /* ensure probs size is 128-bit aligned */
>  	priv_tbl = dma_alloc_coherent(rkvdec->dev, sizeof(*priv_tbl),
>  				      &vp9_ctx->priv_tbl.dma, GFP_KERNEL);
>  	if (!priv_tbl) {