linux-kernel - Re: [PATCH v2] drm/radeon: Fix kernel panic with HDMI w/o SAD

Open Source and information security mailing list archives

Date:	Mon, 5 Jan 2015 12:48:05 -0500
From:	Alex Deucher <alexdeucher@...il.com>
To:	Takashi Iwai <tiwai@...e.de>
Cc:	David Airlie <airlied@...ux.ie>,
	Alex Deucher <alexander.deucher@....com>,
	Christian Koenig <christian.koenig@....com>,
	Maling list - DRI developers 
	<dri-devel@...ts.freedesktop.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] drm/radeon: Fix kernel panic with HDMI w/o SAD

On Mon, Jan 5, 2015 at 12:23 PM, Takashi Iwai <tiwai@...e.de> wrote:
> At Mon, 5 Jan 2015 12:07:52 -0500,
> Alex Deucher wrote:
>>
>> On Sat, Jan 3, 2015 at 5:09 AM, Takashi Iwai <tiwai@...e.de> wrote:
>> > A BUG_ON() call in dce3_2_afmt_write_sad_regs() is triggered when a
>> > HDMI monitor without audio is plugged:
>>
>> I have a slightly different fix already queued up:
>> http://lists.freedesktop.org/archives/dri-devel/2014-December/073672.html
>
> Oh, that's identical with my v1 patch :)  But, with that fix, an error
> message will be shown at each time you plug such a monitor, right?
> This doesn't look right, so I revised the patch.

Yes, but if the monitor claims to support audio, it should supply
SADs.  If it doesn't, the driver has no way of knowing what type of
audio the monitor supports.  I'm fine with removing the error message
or making it debug only however.

>
> Also, can we skip the register write completely?  I thought of a case
> like we replug a monitor from the one with audio to another without
> audio...

Changing the monitor will generally trigger a full probe and modeset
again anyway.  The register writes are just there to pass the audio
information supported by the monitor along to the audio driver.

Alex

>
>
> thanks,
>
> Takashi
>
>>
>> Alex
>>
>> >
>> >  kernel BUG at ../drivers/gpu/drm/radeon/dce3_1_afmt.c:110!
>> >  invalid opcode: 0000 [#1] PREEMPT SMP
>> >  CPU: 2 PID: 967 Comm: Xorg Tainted: PO  3.16.7-7-desktop #1
>> >  Hardware name: System manufacturer System Product Name/M4A77T, BIOS 2401    05/18/2011
>> >  task: ffff8800cea86350 ti: ffff8800c1880000 task.ti: ffff8800c1880000
>> >  RIP: 0010:[<ffffffffa0126c50>] dce3_1_hdmi_setmode+0x570/0x5a0 [radeon]
>> >  Call Trace:
>> >   [<ffffffffa00a6936>] drm_crtc_helper_set_mode+0x346/0x520 [drm_kms_helper]
>> >   [<ffffffffa00a7678>] drm_crtc_helper_set_config+0x8a8/0xad0 [drm_kms_helper]
>> >   [<ffffffffa00ede3f>] radeon_crtc_set_config+0x3f/0x110 [radeon]
>> >   [<ffffffffa001edc1>] drm_mode_set_config_internal+0x61/0xe0 [drm]
>> >   [<ffffffffa00a9a6b>] restore_fbdev_mode+0xab/0xd0 [drm_kms_helper]
>> >   [<ffffffffa00a9aae>] drm_fb_helper_restore_fbdev_mode_unlocked+0x1e/0x30 [drm_kms_helper]
>> >   [<ffffffffa00ab642>] drm_fb_helper_set_par+0x22/0x60 [drm_kms_helper]
>> >   [<ffffffffa00ab5cb>] drm_fb_helper_hotplug_event+0x8b/0xe0 [drm_kms_helper]
>> >   [<ffffffffa00ab65a>] drm_fb_helper_set_par+0x3a/0x60 [drm_kms_helper]
>> >   [<ffffffff813818ce>] fb_set_var+0x15e/0x3b0
>> >   [<ffffffff81378d0b>] fbcon_blank+0x1cb/0x2b0
>> >   [<ffffffff813f2a31>] do_unblank_screen+0xa1/0x1b0
>> >   [<ffffffff813e8fd3>] complete_change_console+0x53/0xe0
>> >   [<ffffffff813e9fa9>] vt_ioctl+0xf49/0x10d0
>> >   [<ffffffff813ddfdc>] tty_ioctl+0x26c/0xb70
>> >   [<ffffffff811cad17>] do_vfs_ioctl+0x2e7/0x4c0
>> >   [<ffffffff811caf71>] SyS_ioctl+0x81/0xa0
>> >   [<ffffffff81622a2d>] system_call_fastpath+0x1a/0x1f
>> >   [<00007f2fae8c6397>] 0x7f2fae8c6396
>> >
>> > Actually the BUG_ON() check is wrong, since sads may be NULL when
>> > sad_count is zero.  This patch removes the BUG_ON() and adds the
>> > proper NULL initialization of sads.
>> >
>> > Bugzilla: https://bugzilla.opensuse.org/show_bug.cgi?id=911356
>> > Cc: <stable@...r.kernel.org>
>> > Signed-off-by: Takashi Iwai <tiwai@...e.de>
>> > ---
>> >  drivers/gpu/drm/radeon/dce3_1_afmt.c | 3 +--
>> >  1 file changed, 1 insertion(+), 2 deletions(-)
>> >
>> > diff --git a/drivers/gpu/drm/radeon/dce3_1_afmt.c b/drivers/gpu/drm/radeon/dce3_1_afmt.c
>> > index 2fe8cfc966d9..7ca23f45829e 100644
>> > --- a/drivers/gpu/drm/radeon/dce3_1_afmt.c
>> > +++ b/drivers/gpu/drm/radeon/dce3_1_afmt.c
>> > @@ -72,7 +72,7 @@ static void dce3_2_afmt_write_sad_regs(struct drm_encoder *encoder)
>> >         struct radeon_device *rdev = encoder->dev->dev_private;
>> >         struct drm_connector *connector;
>> >         struct radeon_connector *radeon_connector = NULL;
>> > -       struct cea_sad *sads;
>> > +       struct cea_sad *sads = NULL;
>> >         int i, sad_count;
>> >
>> >         static const u16 eld_reg_to_type[][2] = {
>> > @@ -107,7 +107,6 @@ static void dce3_2_afmt_write_sad_regs(struct drm_encoder *encoder)
>> >                 DRM_ERROR("Couldn't read SADs: %d\n", sad_count);
>> >                 return;
>> >         }
>> > -       BUG_ON(!sads);
>> >
>> >         for (i = 0; i < ARRAY_SIZE(eld_reg_to_type); i++) {
>> >                 u32 value = 0;
>> > --
>> > 2.2.0
>> >
>> > _______________________________________________
>> > dri-devel mailing list
>> > dri-devel@...ts.freedesktop.org
>> > http://lists.freedesktop.org/mailman/listinfo/dri-devel
>>
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