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

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Date:   Thu, 13 Apr 2023 08:54:58 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Pierre Asselin <pa@...ix.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

"Pierre Asselin" <pa@...ix.com> writes:

[...]

> [    3.343433] sysfb: si->rsvd_size 0 si->rsvd_pos 0

Thanks for confirming this. I was expected that as mentioned since it was
the only reasonable explanation for your problem.

[...]

> What if _depth is low but the rsvd_ are right ?
> Then _width and _linelength would be inconsistent with _depth but
> consistent with the recomputed bits_per_pixel ?  How many ways can the
> firmware lie ?
>

I don't know. But in your case the firmware is not reporting the mode
correctly since it is setting a framebuffer of 1024x768 and xRGB but
is not reporting si->rsvd_size=8 and si->rsvd_pos=24 as it should.

One option is to have a DMI match table similar to what we already have
for EFI machines in drivers/firmware/efi/sysfb_efi.c but also for BIOS.

The question then is if we can trust other systems to report a proper
rsvd_size and rsvd_pos...

> We need more testers, don't we ?
>

It's tricky, yes.

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat