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

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Message-ID: <1de3112b-6349-46d8-b90b-69d0849c7659@suse.de>
Date: Tue, 21 Oct 2025 08:51:09 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Mehdi Ben Hadj Khelifa <mehdi.benhadjkhelifa@...il.com>,
 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

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.

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;

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)