[PATCH] drm/msm/a6xx: Fix excessive stack usage

[Dmitry Baryshkov]

On Sun, Oct 27, 2024 at 11:35:47PM +0530, Akhil P Oommen wrote:
> Clang-19 and above sometimes end up with multiple copies of the large
> a6xx_hfi_msg_bw_table structure on the stack. The problem is that
> a6xx_hfi_send_bw_table() calls a number of device specific functions to
> fill the structure, but these create another copy of the structure on
> the stack which gets copied to the first.
> 
> If the functions get inlined, that busts the warning limit:
> 
> drivers/gpu/drm/msm/adreno/a6xx_hfi.c:631:12: error: stack frame size (1032) exceeds limit (1024) in 'a6xx_hfi_send_bw_table' [-Werror,-Wframe-larger-than]
> 
> Fix this by kmalloc-ating struct a6xx_hfi_msg_bw_table instead of using
> the stack. Also, use this opportunity to skip re-initializing this table
> to optimize gpu wake up latency.
> 
> Cc: Arnd Bergmann <arnd at kernel.org>
> 
> Signed-off-by: Akhil P Oommen <quic_akhilpo at quicinc.com>
> ---
>  drivers/gpu/drm/msm/adreno/a6xx_gmu.h |  1 +
>  drivers/gpu/drm/msm/adreno/a6xx_hfi.c | 34 ++++++++++++++++++++++------------
>  2 files changed, 23 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gmu.h b/drivers/gpu/drm/msm/adreno/a6xx_gmu.h
> index 94b6c5cab6f4..b4a79f88ccf4 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gmu.h
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gmu.h
> @@ -99,6 +99,7 @@ struct a6xx_gmu {
>  	struct completion pd_gate;
>  
>  	struct qmp *qmp;
> +	struct a6xx_hfi_msg_bw_table *bw_table;
>  };
>  
>  static inline u32 gmu_read(struct a6xx_gmu *gmu, u32 offset)
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_hfi.c b/drivers/gpu/drm/msm/adreno/a6xx_hfi.c
> index cdb3f6e74d3e..55e51c81be1f 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_hfi.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_hfi.c
> @@ -630,32 +630,42 @@ static void a6xx_build_bw_table(struct a6xx_hfi_msg_bw_table *msg)
>  
>  static int a6xx_hfi_send_bw_table(struct a6xx_gmu *gmu)
>  {
> -	struct a6xx_hfi_msg_bw_table msg = { 0 };
> +	struct a6xx_hfi_msg_bw_table *msg;
>  	struct a6xx_gpu *a6xx_gpu = container_of(gmu, struct a6xx_gpu, gmu);
>  	struct adreno_gpu *adreno_gpu = &a6xx_gpu->base;
>  
> +	if (gmu->bw_table)
> +		goto send;
> +
> +	msg = devm_kzalloc(gmu->dev, sizeof(*msg), GFP_KERNEL);

Is it necessary after being sent? Isn't it better to just kzalloc() it
and then kfree() it at the end of the function?

> +	if (!msg)
> +		return -ENOMEM;
> +
>  	if (adreno_is_a618(adreno_gpu))
> -		a618_build_bw_table(&msg);
> +		a618_build_bw_table(msg);
>  	else if (adreno_is_a619(adreno_gpu))
> -		a619_build_bw_table(&msg);
> +		a619_build_bw_table(msg);
>  	else if (adreno_is_a640_family(adreno_gpu))
> -		a640_build_bw_table(&msg);
> +		a640_build_bw_table(msg);
>  	else if (adreno_is_a650(adreno_gpu))
> -		a650_build_bw_table(&msg);
> +		a650_build_bw_table(msg);
>  	else if (adreno_is_7c3(adreno_gpu))
> -		adreno_7c3_build_bw_table(&msg);
> +		adreno_7c3_build_bw_table(msg);
>  	else if (adreno_is_a660(adreno_gpu))
> -		a660_build_bw_table(&msg);
> +		a660_build_bw_table(msg);
>  	else if (adreno_is_a690(adreno_gpu))
> -		a690_build_bw_table(&msg);
> +		a690_build_bw_table(msg);
>  	else if (adreno_is_a730(adreno_gpu))
> -		a730_build_bw_table(&msg);
> +		a730_build_bw_table(msg);
>  	else if (adreno_is_a740_family(adreno_gpu))
> -		a740_build_bw_table(&msg);
> +		a740_build_bw_table(msg);
>  	else
> -		a6xx_build_bw_table(&msg);
> +		a6xx_build_bw_table(msg);
> +
> +	gmu->bw_table = msg;
>  
> -	return a6xx_hfi_send_msg(gmu, HFI_H2F_MSG_BW_TABLE, &msg, sizeof(msg),
> +send:
> +	return a6xx_hfi_send_msg(gmu, HFI_H2F_MSG_BW_TABLE, gmu->bw_table, sizeof(*(gmu->bw_table)),
>  		NULL, 0);
>  }
>  
> 
> ---
> base-commit: 74c374648ed08efb2ef339656f2764c28c046956
> change-id: 20241024-stack-size-fix-28af7abd3fab
> 
> Best regards,
> -- 
> Akhil P Oommen <quic_akhilpo at quicinc.com>
> 

-- 
With best wishes
Dmitry