linux-kernel - Re: [PATCH v3] simplefb: Enable boot time VESA graphic mode selection.

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Date:   Wed, 23 Feb 2022 20:55:57 +0100
From:   Michal Suchánek <msuchanek@...e.de>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Martin Mares <mj@....cz>,
        Helge Deller <deller@....de>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Sudeep Holla <sudeep.holla@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Cristian Marussi <cristian.marussi@....com>,
        Simon Trimmer <simont@...nsource.cirrus.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rob Herring <robh@...nel.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        David Herrmann <dh.herrmann@...il.com>,
        linux-kernel@...r.kernel.org, linux-video@...ey.karlin.mff.cuni.cz
Subject: Re: [PATCH v3] simplefb: Enable boot time VESA graphic mode
 selection.

On Wed, Feb 23, 2022 at 07:34:54PM +0100, Javier Martinez Canillas wrote:
> On 2/23/22 19:23, Michal Suchánek wrote:
> 
> [snip]
> 
> >> My point about the subject line remains thought, I would use something like:
> >>
> >> firmware: sysfb: Enable boot time VESA graphic mode selection for simplefb
> > 
> > I see where the confusion comes from.
> >
> 
> Yeah. And just to clarify, the "simplefb" in the subject line I proposed
> was about the sysfb simplefb and not the fbdev simplefb :)
>  
> > The efifb (and probably vesafb) has implicit unstated dependency on
> > sysfb. So the drivers that select BOOT_VESA_SUPPORT should instead
> > depend on SYSFB, and then SYSFB can select BOOT_VESA_SUPPORT, and it
> > will look much saner.
> >
> 
> That indeed would be much nicer. And I agree with you that there's an
> implicit dependency that should be made explicit since SYSFB is what
> registers the "efi-framebuffer" or "vesa-framebuffer" if SYSFB_SIMPLEFB
> is not enabled.
> 
> Should SYSFB should only select BOOT_VESA_SUPPORT if x86 ? I know that
> in practice shouldn't matter because BOOT_VESA_SUPPORT is under x86 but
> I guess is more correct if that's the case.

Part of the reason to move it to x86 is to avoid the conditional.
Technically there is nothing stopping other platforms from running the
VESA BIOS, it's just not very practical.

> And I think that FB_SIMPLE should depend on SYSFB_SIMPLEFB if !OF (since
> a "simple-framebuffer" platform device could be registered by OF if a
> Device Tree node with compatible "simple-framebuffer" exists).

So generally SYSFB_SIMPLEFB || OF. The part that you can enable the
driver and it does not do anything because you are missing
SYSFB_SIMPLEFB is indeed confusing. There is a comment in SIMLEDRM
description but not FB_SIMPLE.

Then there is the part that if neither simplefb nor vesafb nor efifb nor
offb is built then the sysfb code is unused.

Thanks

Michal