linux-kernel - [PATCH] firmware/sysfb: Fix wrong stride when bits-per-pixel is calculated

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Date:   Wed, 12 Apr 2023 17:02:25 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Pierre Asselin <pa@...ix.com>,
        Jocelyn Falempe <jfalempe@...hat.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        dri-devel@...ts.freedesktop.org,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>
Subject: [PATCH] firmware/sysfb: Fix wrong stride when bits-per-pixel is calculated

The commit f35cd3fa7729 ("firmware/sysfb: Fix EFI/VESA format selection")
fixed format selection, by calculating the bits-per-pixel instead of just
using the reported color depth.

But unfortunately this broke some modes because the stride is always set
to the reported line length (in bytes), which could not match the actual
stride if the calculated bits-per-pixel doesn't match the reported depth.

Fixes: f35cd3fa7729 ("firmware/sysfb: Fix EFI/VESA format selection")
Reported-by: Pierre Asselin <pa@...ix.com>
Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
---

 drivers/firmware/sysfb_simplefb.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/firmware/sysfb_simplefb.c b/drivers/firmware/sysfb_simplefb.c
index 82c64cb9f531..5dc23e57089f 100644
--- a/drivers/firmware/sysfb_simplefb.c
+++ b/drivers/firmware/sysfb_simplefb.c
@@ -28,7 +28,7 @@ __init bool sysfb_parse_mode(const struct screen_info *si,
 			     struct simplefb_platform_data *mode)
 {
 	__u8 type;
-	u32 bits_per_pixel;
+	u32 bits_per_pixel, stride;
 	unsigned int i;
 
 	type = si->orig_video_isVGA;
@@ -54,14 +54,19 @@ __init bool sysfb_parse_mode(const struct screen_info *si,
 	 * bits_per_pixel here and ignore lfb_depth. In the loop below,
 	 * ignore simplefb formats with alpha bits, as EFI and VESA
 	 * don't specify alpha channels.
+	 *
+	 * If a calculated bits_per_pixel is used instead of lfb_depth,
+	 * then also ignore lfb_linelength and calculate the stride.
 	 */
 	if (si->lfb_depth > 8) {
 		bits_per_pixel = max(max3(si->red_size + si->red_pos,
 					  si->green_size + si->green_pos,
 					  si->blue_size + si->blue_pos),
 				     si->rsvd_size + si->rsvd_pos);
+		stride = DIV_ROUND_UP(si->lfb_width * bits_per_pixel, 8);
 	} else {
 		bits_per_pixel = si->lfb_depth;
+		stride = si->lfb_linelength;
 	}
 
 	for (i = 0; i < ARRAY_SIZE(formats); ++i) {
@@ -80,7 +85,7 @@ __init bool sysfb_parse_mode(const struct screen_info *si,
 			mode->format = f->name;
 			mode->width = si->lfb_width;
 			mode->height = si->lfb_height;
-			mode->stride = si->lfb_linelength;
+			mode->stride = stride;
 			return true;
 		}
 	}

base-commit: e62252bc55b6d4eddc6c2bdbf95a448180d6a08d
-- 
2.40.0