linux-kernel - Re: [PATCH] drm/tiny: Refactor framebuffer's size calculation

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Message-ID: <6a917f07-18dd-4f8f-bfc5-b85d9051339d@gmail.com>
Date: Tue, 21 Oct 2025 09:41:49 +0100
From: Mehdi Ben Hadj Khelifa <mehdi.benhadjkhelifa@...il.com>
To: Thomas Zimmermann <tzimmermann@...e.de>, lanzano.alex@...il.com,
 maarten.lankhorst@...ux.intel.com, mripard@...nel.org, airlied@...il.com,
 simona@...ll.ch
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
 skhan@...uxfoundation.org, david.hunter.linux@...il.com, khalid@...nel.org,
 linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH] drm/tiny: Refactor framebuffer's size calculation

On 10/21/25 7:51 AM, Thomas Zimmermann wrote:
> Hi
> 
> Am 20.10.25 um 13:57 schrieb Mehdi Ben Hadj Khelifa:
>> Use drm_format_info_min_pitch() to calculate the framebuffer line pitch
>> instead of directly multiplying width and height. This aligns with DRM
>> helpers for determining per-line byte size and avoids manual assumptions
>> about bytes per pixel.
>>
>> Suggested-by: Thomas Zimmermann <tzimmermann@...e.de>
>> Signed-off-by: Mehdi Ben Hadj Khelifa <mehdi.benhadjkhelifa@...il.com>
>> ---
>>   drivers/gpu/drm/tiny/repaper.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/tiny/repaper.c b/drivers/gpu/drm/tiny/ 
>> repaper.c
>> index 4824f863fdba..aeff49bc6ba7 100644
>> --- a/drivers/gpu/drm/tiny/repaper.c
>> +++ b/drivers/gpu/drm/tiny/repaper.c
>> @@ -517,6 +517,8 @@ static int repaper_fb_dirty(struct drm_framebuffer 
>> *fb, const struct iosys_map *
>>       unsigned int dst_pitch = 0;
>>       struct iosys_map dst;
>>       struct drm_rect clip;
>> +    const struct drm_format_info *info = fb->format;
> 
> This is the wrong format. You're allocating the output buffer here, but 
> you're using the input format. IIUC the output format is DRM_FORMAT_R1. 
> The input is _XRGB8888.
> 
Ah. Thanks for clarification.I thought since it had the same output 
format. I will send a v3 shortly.> Best regards
> Thomas
> 
>> +    size_t pitch;
>>       int idx, ret = 0;
>>       u8 *buf = NULL;
>> @@ -534,7 +536,9 @@ static int repaper_fb_dirty(struct drm_framebuffer 
>> *fb, const struct iosys_map *
>>       DRM_DEBUG("Flushing [FB:%d] st=%ums\n", fb->base.id,
>>             epd->factored_stage_time);
>> -    buf = kmalloc(fb->width * fb->height / 8, GFP_KERNEL);
>> +    pitch = drm_format_info_min_pitch(info, 0, fb->width);
>> +
>> +    buf = kmalloc_array(fb->height, pitch, GFP_KERNEL);
>>       if (!buf) {
>>           ret = -ENOMEM;
>>           goto out_exit;
>