linux-kernel - Re: [PATCH 2/2] drm/msm/dsi: fix 32-bit signed integer extension in pclk

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Message-ID: <mk5mrypbeeuzhcmqimck42gnykjwj3yz6ua4npkxymrvho6z7i@dvvrxsafqcxj>
Date: Sun, 6 Oct 2024 20:32:38 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Jonathan Marek <jonathan@...ek.ca>
Cc: freedreno@...ts.freedesktop.org, Rob Clark <robdclark@...il.com>, 
	Abhinav Kumar <quic_abhinavk@...cinc.com>, Sean Paul <sean@...rly.run>, 
	Marijn Suijten <marijn.suijten@...ainline.org>, David Airlie <airlied@...il.com>, 
	Simona Vetter <simona@...ll.ch>, Jessica Zhang <quic_jesszhan@...cinc.com>, 
	Konrad Dybcio <konradybcio@...nel.org>, 
	"open list:DRM DRIVER for Qualcomm display hardware" <linux-arm-msm@...r.kernel.org>, 
	"open list:DRM DRIVER for Qualcomm display hardware" <dri-devel@...ts.freedesktop.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] drm/msm/dsi: fix 32-bit signed integer extension in
 pclk_rate calculation

On Sat, Oct 05, 2024 at 10:38:10AM GMT, Jonathan Marek wrote:
> When (mode->clock * 1000) is larger than (1<<31), int to unsigned long
> conversion will sign extend the int to 64 bits and the pclk_rate value
> will be incorrect.
> 
> Fix this by making the result of the multiplication unsigned.
> 
> Note that above (1<<32) would still be broken and require more changes, but
> its unlikely anyone will need that anytime soon.
> 

Fixes?

> Signed-off-by: Jonathan Marek <jonathan@...ek.ca>
> ---
>  drivers/gpu/drm/msm/dsi/dsi_host.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index 1205aa398e445..a98d24b7cb00b 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -550,7 +550,7 @@ static unsigned long dsi_get_pclk_rate(const struct drm_display_mode *mode,
>  {
>  	unsigned long pclk_rate;
>  
> -	pclk_rate = mode->clock * 1000;
> +	pclk_rate = mode->clock * 1000u;
>  
>  	if (dsc)
>  		pclk_rate = dsi_adjust_pclk_for_compression(mode, dsc);
> -- 
> 2.45.1
> 

-- 
With best wishes
Dmitry