Re: [PATCH 2/2] media: rkvdec: reduce stack usage in rkvdec_init_v4l2_vp9_count_tbl()

[Nicolas Dufresne <nicolas.dufresne@collabora.com>]

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Le lundi 02 février 2026 à 10:47 +0100, Arnd Bergmann a écrit :
> From: Arnd Bergmann <arnd@arndb.de>
> 
> The deeply nested loop in rkvdec_init_v4l2_vp9_count_tbl() needs a lot
> of registers, so when the clang register allocator runs out, it ends up
> spilling countless temporaries to the stack:
> 
> drivers/media/platform/rockchip/rkvdec/rkvdec-vp9.c:966:12: error: stack frame size (1472) exceeds limit (1280) in 'rkvdec_vp9_start' [-Werror,-Wframe-larger-than]
> 
> Marking this function as noinline_for_stack keeps it out of
> rkvdec_vp9_start(), giving the compiler more room for optimization.
> 
> The resulting code is good enough that both the total stack usage
> and the loop get enough better to stay under the warning limit,
> though it's still slow, and would need a larger rework if this
> function ends up being called in a fast path.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

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

> ---
>  drivers/media/platform/rockchip/rkvdec/rkvdec-vp9.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/media/platform/rockchip/rkvdec/rkvdec-vp9.c b/drivers/media/platform/rockchip/rkvdec/rkvdec-vp9.c
> index ba51a7c2fe55..1c875d5a2bac 100644
> --- a/drivers/media/platform/rockchip/rkvdec/rkvdec-vp9.c
> +++ b/drivers/media/platform/rockchip/rkvdec/rkvdec-vp9.c
> @@ -893,7 +893,8 @@ static void rkvdec_vp9_done(struct rkvdec_ctx *ctx,
>  	update_ctx_last_info(vp9_ctx);
>  }
>  
> -static void rkvdec_init_v4l2_vp9_count_tbl(struct rkvdec_ctx *ctx)
> +static noinline_for_stack void
> +rkvdec_init_v4l2_vp9_count_tbl(struct rkvdec_ctx *ctx)
>  {
>  	struct rkvdec_vp9_ctx *vp9_ctx = ctx->priv;
>  	struct rkvdec_vp9_intra_frame_symbol_counts *intra_cnts = vp9_ctx->count_tbl.cpu;

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