linux-kernel - Re: cirrusdrmfb broken with simplefb

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Message-ID: <CANq1E4TW3O9czVzX1bj4F5oMrDHZ+ZsLHLCk9ANsg2e14QXmfg@mail.gmail.com>
Date:	Thu, 19 Dec 2013 13:36:38 +0100
From:	David Herrmann <dh.herrmann@...il.com>
To:	Takashi Iwai <tiwai@...e.de>
Cc:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Ingo Molnar <mingo@...nel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	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 12:06 PM, Takashi Iwai <tiwai@...e.de> wrote:
> At Thu, 19 Dec 2013 11:46:51 +0100,
> David Herrmann 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..
>
> You can set FB_SIMPLE default value depending on X86_SYSFB, something
> like:
>
> --- a/drivers/video/Kconfig
> +++ b/drivers/video/Kconfig
> @@ -2455,6 +2455,7 @@ config FB_HYPERV
>  config FB_SIMPLE
>         bool "Simple framebuffer support"
>         depends on (FB = y)
> +       default y if X86_SYSFB
>         select FB_CFB_FILLRECT
>         select FB_CFB_COPYAREA
>         select FB_CFB_IMAGEBLIT

The "default <wx> if <yz>" only works if the config hasn't been set at
all, yet. Even a "# CONFIG_* is unset" causes the "default" value to
be ignored.

How about adding "depends on (FB_SIMPLE = y)" for X86_SYSFB? I guess I
will try that and send a patch.

Thanks
David
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