linux-kernel - Re: cirrusdrmfb broken with simplefb

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Message-ID: <CANq1E4R5fF+Xtub8E_64bh6akZi8uU6d2ntG-rzsc_D7KFBY=g@mail.gmail.com>
Date:	Thu, 19 Dec 2013 13:39:08 +0100
From:	David Herrmann <dh.herrmann@...il.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Takashi Iwai <tiwai@...e.de>,
	Stephen Warren <swarren@...dotorg.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	"the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: cirrusdrmfb broken with simplefb

Hi

On Thu, Dec 19, 2013 at 1:31 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * David Herrmann <dh.herrmann@...il.com> wrote:
>
>> Hi
>>
>> On Thu, Dec 19, 2013 at 1:03 AM, One Thousand Gnomes
>> <gnomes@...rguk.ukuu.org.uk> wrote:
>> >> > That bug always existed, simplefb is just the first driver to hit it
>> >> > (vesafb/efifb didn't use resources). I'm aware of the issue but as a
>> >> > workaround you can simply disable CONFIG_X86_SYSFB. That restores
>> >> > the old behavior.
>> >>
>> >> This looks like a regression, so we'll either need a fix or we'll have
>> >> to mark CONFIG_X86_SYSFB as CONFIG_BROKEN.
>> >
>> > Kernel bugzilla has entries for simplefb breaking both vesafb and
>> > matrox mga.
>>
>> Thanks for the hints. I've read through all I could find and tried
>> to provide some help.
>>
>> I'm kind of confused, most of them enable CONFIG_X86_SYSFB (which is
>> 'n' by default) but don't read the help text. I did my best to tell
>> people that this option requires CONFIG_FB_SIMPLE, but if you don't
>> read the help-text you won't notice that. Don't know what to do
>> about that..
>
> People generally don't read the help text - still the kernel should
> not break. So please the Kconfig angle (and the bootup logic, etc.)
> fool-proof, graphics failures are not fun to debug!

There're dozens of combinations that break gfx-boot. Even non-obvious
things like disabling VT_HW_CONSOLE_BINDING will break gfx-handover.
Anyhow, bad examples are no excuse.. I will send patches to fool-proof
sysfb.

David
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