linux-kernel - Re: [PATCH v2 3/4] drm/mediatek: Add casting before assign

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Date:   Wed, 14 Jun 2023 10:43:08 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     "Jason-JH.Lin" <jason-jh.lin@...iatek.com>,
        Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Alexandre Mergnat <amergnat@...libre.com>
Cc:     Matthias Brugger <matthias.bgg@...il.com>,
        Rex-BC Chen <rex-bc.chen@...iatek.com>,
        Jason-ch Chen <jason-ch.chen@...iatek.com>,
        Johnson Wang <johnson.wang@...iatek.com>,
        Singo Chang <singo.chang@...iatek.com>,
        Nancy Lin <nancy.lin@...iatek.com>,
        Shawn Sung <shawn.sung@...iatek.com>,
        dri-devel@...ts.freedesktop.org,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Project_Global_Chrome_Upstream_Group@...iatek.com
Subject: Re: [PATCH v2 3/4] drm/mediatek: Add casting before assign

Il 13/06/23 13:32, Jason-JH.Lin ha scritto:
> 1. Add casting before assign to avoid the unintentional integer
>     overflow or unintended sign extension.
> 2. Add a int varriable for multiplier calculation instead of calculating
>     different types multiplier with dma_addr_t varriable directly.
> 
> Signed-off-by: Jason-JH.Lin <jason-jh.lin@...iatek.com>
> Fixes: 1a64a7aff8da ("drm/mediatek: Fix cursor plane no update")
> ---
>   drivers/gpu/drm/mediatek/mtk_drm_gem.c   |  2 +-
>   drivers/gpu/drm/mediatek/mtk_drm_plane.c | 22 +++++++++++++---------
>   2 files changed, 14 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_gem.c b/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> index a25b28d3ee90..0c7878bc0b37 100644
> --- a/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_gem.c
> @@ -121,7 +121,7 @@ int mtk_drm_gem_dumb_create(struct drm_file *file_priv, struct drm_device *dev,
>   	int ret;
>   
>   	args->pitch = DIV_ROUND_UP(args->width * args->bpp, 8);
> -	args->size = args->pitch * args->height;
> +	args->size = (__u64)args->pitch * args->height;

We could avoid explicit casting here if you do

	args->size = args->pitch;
	args->size *= args->height;

>   
>   	mtk_gem = mtk_drm_gem_create(dev, args->size, false);
>   	if (IS_ERR(mtk_gem))
> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_plane.c b/drivers/gpu/drm/mediatek/mtk_drm_plane.c
> index 31f9420aff6f..1cd41454d545 100644
> --- a/drivers/gpu/drm/mediatek/mtk_drm_plane.c
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_plane.c
> @@ -145,6 +145,7 @@ static void mtk_plane_update_new_state(struct drm_plane_state *new_state,
>   	dma_addr_t addr;
>   	dma_addr_t hdr_addr = 0;
>   	unsigned int hdr_pitch = 0;
> +	int offset;

...but offset can never be negative, can it?
in that case, this should be unsigned int.

>   
>   	gem = fb->obj[0];
>   	mtk_gem = to_mtk_gem_obj(gem);
> @@ -154,8 +155,10 @@ static void mtk_plane_update_new_state(struct drm_plane_state *new_state,
>   	modifier = fb->modifier;
>   
>   	if (modifier == DRM_FORMAT_MOD_LINEAR) {
> -		addr += (new_state->src.x1 >> 16) * fb->format->cpp[0];
> -		addr += (new_state->src.y1 >> 16) * pitch;
> +		offset = (new_state->src.x1 >> 16) * fb->format->cpp[0];
> +		addr += offset;
> +		offset = (new_state->src.y1 >> 16) * pitch;
> +		addr += offset;
>   	} else {
>   		int width_in_blocks = ALIGN(fb->width, AFBC_DATA_BLOCK_WIDTH)
>   				      / AFBC_DATA_BLOCK_WIDTH;
> @@ -163,21 +166,22 @@ static void mtk_plane_update_new_state(struct drm_plane_state *new_state,
>   				       / AFBC_DATA_BLOCK_HEIGHT;
>   		int x_offset_in_blocks = (new_state->src.x1 >> 16) / AFBC_DATA_BLOCK_WIDTH;
>   		int y_offset_in_blocks = (new_state->src.y1 >> 16) / AFBC_DATA_BLOCK_HEIGHT;
> -		int hdr_size;
> +		int hdr_size, hdr_offset;
>   
>   		hdr_pitch = width_in_blocks * AFBC_HEADER_BLOCK_SIZE;
>   		pitch = width_in_blocks * AFBC_DATA_BLOCK_WIDTH *
>   			AFBC_DATA_BLOCK_HEIGHT * fb->format->cpp[0];
>   
>   		hdr_size = ALIGN(hdr_pitch * height_in_blocks, AFBC_HEADER_ALIGNMENT);
> +		hdr_offset = hdr_pitch * y_offset_in_blocks +
> +			AFBC_HEADER_BLOCK_SIZE * x_offset_in_blocks;
> +		hdr_addr = addr + hdr_offset;
>   
> -		hdr_addr = addr + hdr_pitch * y_offset_in_blocks +
> -			   AFBC_HEADER_BLOCK_SIZE * x_offset_in_blocks;
>   		/* The data plane is offset by 1 additional block. */
> -		addr = addr + hdr_size +
> -		       pitch * y_offset_in_blocks +
> -		       AFBC_DATA_BLOCK_WIDTH * AFBC_DATA_BLOCK_HEIGHT *
> -		       fb->format->cpp[0] * (x_offset_in_blocks + 1);
> +		offset = pitch * y_offset_in_blocks +
> +			 AFBC_DATA_BLOCK_WIDTH * AFBC_DATA_BLOCK_HEIGHT *
> +			 fb->format->cpp[0] * (x_offset_in_blocks + 1);
> +		addr = addr + hdr_size + offset;
>   	}
>   
>   	mtk_plane_state->pending.enable = true;