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From:   Javier Martinez Canillas <javierm@redhat.com>
To:     Pierre Asselin <pa@panix.com>
Cc:     Pierre Asselin <pa@panix.com>,
        Jocelyn Falempe <jfalempe@redhat.com>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
        Hans de Goede <hdegoede@redhat.com>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Ard Biesheuvel <ardb@kernel.org>
Subject: Re: [PATCH] firmware/sysfb: Fix wrong stride when bits-per-pixel is
 calculated
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Date:   Thu, 13 Apr 2023 00:09:27 +0200
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"Pierre Asselin" <pa@panix.com> writes:

>> Javier Martinez Canillas <javierm@redhat.com> writes:
>>
>> I still don't understand why this particular configuration didn't work...
>>
>> The framebuffer starts at 0xd8000000 and has a size of 0x240000 bytes, so
>
> Says who ?  It's the same grub, same video mode as before the regression,
> so the size is probably 0x300000 like it always was.
>
>> a r8g8b8 pixel format with resolution 1024x768 should be correct. Since is
>> 1024 * 768 * (24 / 8) = 2359296 = 0x240000.
>
> That is internally consistent, but at variance with the video mode
> set up by grub.
>
> It is better to sqeeze bits by 4:3 on each line (regression) than to
> scatter 4 logical lines across 3 physical lines (regression, patched) !
>

Indeed. I noticed now that the IORESOURCE_MEM is set-up in the function
sysfb_create_simplefb() so is likely that is internally consistent as you
said but wrong :)

>> Could you please apply the following diff that will print all the relevant
>> fields from the screen_info that are used to calculate the bpp and stride.
>
> YES !  I can't peer into that struct screen_info and I don't know to
> write the printk's.  (Hm, doesn't look too hard, but trust me, I would
> fumble it.)
>
> I'll back out the original patch first.
> Stand by.
>
> --PA
>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat