Re: [PATCH] drm/radeon: Fix kernel panic when plugging a HDMI w/o SAD

[Takashi Iwai <tiwai@suse.de>]

At Sat,  3 Jan 2015 09:27:52 +0100,
Takashi Iwai wrote:
> 
> A BUG_ON() call in dce3_2_afmt_write_sad_regs() is triggered when a
> HDMI monitor without SAD is plugged as the case sad_count = 0 is
> overlooked in the code:
> 
>  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
> 
> This patch fixes it by covering sad_count = 0 in the error check
> properly, too.
> 
> Bugzilla: https://bugzilla.opensuse.org/show_bug.cgi?id=911356
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Takashi Iwai <tiwai@suse.de>
> ---
> 
> IMO, BUG_ON() call itself is exaggerated there, but we may change it later
> independently from this fix.
> 
>  drivers/gpu/drm/radeon/dce3_1_afmt.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/radeon/dce3_1_afmt.c b/drivers/gpu/drm/radeon/dce3_1_afmt.c
> index 2fe8cfc966d9..bafdf92a5732 100644
> --- a/drivers/gpu/drm/radeon/dce3_1_afmt.c
> +++ b/drivers/gpu/drm/radeon/dce3_1_afmt.c
> @@ -103,7 +103,7 @@ static void dce3_2_afmt_write_sad_regs(struct drm_encoder *encoder)
>  	}
>  
>  	sad_count = drm_edid_to_sad(radeon_connector->edid, &sads);
> -	if (sad_count < 0) {
> +	if (sad_count <= 0) {
>  		DRM_ERROR("Couldn't read SADs: %d\n", sad_count);
>  		return;
>  	}

Looking back at this fix again, this seems suboptimal, as it prints
the error even in the correct case (sad_count = 0), and it doesn't set
the register in the later code.  I'm going to post a revised patch.


Takashi