linux-kernel - Re: [PATCH] drm/drm_vblank.c: avoid unsigned int to signed int cast

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Message-ID: <530369f4-1edd-d8cf-031e-a8effdf15510@189.cn>
Date:   Wed, 17 May 2023 01:13:30 +0800
From:   Sui Jingfeng <15330273260@....cn>
To:     Thomas Zimmermann <tzimmermann@...e.de>,
        Sui Jingfeng <suijingfeng@...ngson.cn>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/drm_vblank.c: avoid unsigned int to signed int cast

Hi,

On 2023/5/17 01:06, Thomas Zimmermann wrote:
>
>
> Am 16.05.23 um 18:59 schrieb Sui Jingfeng:
>> Both mode->crtc_htotal and mode->crtc_vtotal are u16 type,
>> mode->crtc_htotal * mode->crtc_vtotal will results a unsigned type.
>> Using a u32 is enough to store the result, but considering that the
>> result will be casted to u64 soon after. We use a u64 type directly.
>>
>> So there no need to cast it to signed type and cast back then.
>>
>> Signed-off-by: Sui Jingfeng <suijingfeng@...ngson.cn>
>> Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
>> Cc: Maxime Ripard <mripard@...nel.org>
>> Cc: Thomas Zimmermann <tzimmermann@...e.de>
>> Cc: David Airlie <airlied@...il.com>
>> Cc: Daniel Vetter <daniel@...ll.ch>
>> Cc: dri-devel@...ts.freedesktop.org
>> Cc: linux-kernel@...r.kernel.org
>
> Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>
>
Thanks a lot,  thanks for the response time also.

>> ---
>>   drivers/gpu/drm/drm_vblank.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
>> index 877e2067534f..d99c404b181b 100644
>> --- a/drivers/gpu/drm/drm_vblank.c
>> +++ b/drivers/gpu/drm/drm_vblank.c
>> @@ -622,7 +622,7 @@ void drm_calc_timestamping_constants(struct 
>> drm_crtc *crtc,
>>         /* Valid dotclock? */
>>       if (dotclock > 0) {
>> -        int frame_size = mode->crtc_htotal * mode->crtc_vtotal;
>> +        u64 frame_size = mode->crtc_htotal * mode->crtc_vtotal;
>>             /*
>>            * Convert scanline length in pixels and video
>> @@ -630,7 +630,7 @@ void drm_calc_timestamping_constants(struct 
>> drm_crtc *crtc,
>>            * in nanoseconds:
>>            */
>>           linedur_ns  = div_u64((u64) mode->crtc_htotal * 1000000, 
>> dotclock);
>> -        framedur_ns = div_u64((u64) frame_size * 1000000, dotclock);
>> +        framedur_ns = div_u64(frame_size * 1000000, dotclock);
>>             /*
>>            * Fields of interlaced scanout modes are only half a frame 
>> duration.
>