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

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Date:   Wed, 12 Apr 2023 14:51:10 -0400
From:   "Pierre Asselin" <pa@...ix.com>
To:     "Javier Martinez Canillas" <javierm@...hat.com>
Cc:     "Pierre Asselin" <pa@...ix.com>,
        "Jocelyn Falempe" <jfalempe@...hat.com>,
        "Daniel Vetter" <daniel.vetter@...ll.ch>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        "Hans de Goede" <hdegoede@...hat.com>,
        "Thomas Zimmermann" <tzimmermann@...e.de>,
        "Ard Biesheuvel" <ardb@...nel.org>
Subject: Re: [PATCH] firmware/sysfb: Fix wrong stride when bits-per-pixel is
 calculated

> And can you share the "linelength=" print out from simplefb ?

Okay.  Three cases, see below.

Your patch tries to fix the stride, but what if it's the _depth_
that's wrong ?  Grub sets the mode, the pre-regression kernel picks this:
    format=x8r8g8b8, mode=1024x768x32, linelength=4096

========== Good ======================================================
grub: gfxpayload=1024x768x24
[    0.003333] Console: colour dummy device 128x48
[    0.003333] printk: console [tty0] enabled
[    0.417054] fbcon: Taking over console
[    0.513399] pci 0000:01:05.0: vgaarb: setting as boot VGA device
[    0.513431] pci 0000:01:05.0: vgaarb: bridge control possible
[    0.513455] pci 0000:01:05.0: vgaarb: VGA device added:
decodes=io+mem,owns=io+mem,locks=none
[    0.513490] vgaarb: loaded
[    3.337529] simple-framebuffer simple-framebuffer.0: framebuffer at
0xd8000000, 0x240000 bytes
[    3.337567] simple-framebuffer simple-framebuffer.0: format=r8g8b8,
mode=1024x768x24, linelength=3072
[    3.338000] Console: switching to colour frame buffer device 128x48
[    3.566490] simple-framebuffer simple-framebuffer.0: fb0: simplefb
registered!

========== Bad after patch, typing blind to log in !==================
grub: gfxpayload=keep
[    0.003333] Console: colour dummy device 128x48
[    0.003333] printk: console [tty0] enabled
[    0.423925] fbcon: Taking over console
[    0.520030] pci 0000:01:05.0: vgaarb: setting as boot VGA device
[    0.520061] pci 0000:01:05.0: vgaarb: bridge control possible
[    0.520085] pci 0000:01:05.0: vgaarb: VGA device added:
decodes=io+mem,owns=io+mem,locks=none
[    0.520120] vgaarb: loaded
[    3.290444] simple-framebuffer simple-framebuffer.0: framebuffer at
0xd8000000, 0x240000 bytes
[    3.290483] simple-framebuffer simple-framebuffer.0: format=r8g8b8,
mode=1024x768x24, linelength=3072
[    3.290916] Console: switching to colour frame buffer device 128x48
[    3.519523] simple-framebuffer simple-framebuffer.0: fb0: simplefb
registered!

========== Good, earlier kernel before regression ====================
grub: gfxpayload=keep
[    0.226675] Console: colour dummy device 128x48
[    0.228643] printk: console [tty0] enabled
[    0.429214] fbcon: Taking over console
[    0.524994] pci 0000:01:05.0: vgaarb: setting as boot VGA device
[    0.525025] pci 0000:01:05.0: vgaarb: bridge control possible
[    0.525049] pci 0000:01:05.0: vgaarb: VGA device added:
decodes=io+mem,owns=io+mem,locks=none
[    0.525082] vgaarb: loaded
[    3.320474] simple-framebuffer simple-framebuffer.0: framebuffer at
0xd8000000, 0x300000 bytes
[    3.320513] simple-framebuffer simple-framebuffer.0: format=x8r8g8b8,
mode=1024x768x32, linelength=4096
[    3.320983] Console: switching to colour frame buffer device 128x48
[    3.415643] simple-framebuffer simple-framebuffer.0: fb0: simplefb
registered!