linux-kernel - Re: cirrusdrmfb broken with simplefb

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <s5hppotrn5l.wl%tiwai@suse.de>
Date:	Thu, 19 Dec 2013 14:22:14 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	David Herrmann <dh.herrmann@...il.com>
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

At Thu, 19 Dec 2013 13:36:38 +0100,
David Herrmann wrote:
> 
> 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.

Yes.  I didn't suggest the strict dependency like below, just because
I assumed you didn't add it intentionally.

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

That's in general a bad approach.  If the strict dependency is
allowed, a more intuitive way is to give a reverse selection.  But
then you'd need to correct the help text, too, as it's implemented
already as a dependency.

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2299,6 +2299,7 @@ source "drivers/rapidio/Kconfig"
 
 config X86_SYSFB
 	bool "Mark VGA/VBE/EFI FB as generic system framebuffer"
+	select SIMPLE_FB
 	help
 	  Firmwares often provide initial graphics framebuffers so the BIOS,
 	  bootloader or kernel can show basic video-output during boot for


Takashi
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/