linux-kernel - Re: [PATCH 2.6.38-10-generic] device driver: fix oops in radeon driver due to incorrect value from hardware

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Date:	Wed, 10 Aug 2011 11:24:31 +0200
From:	Michel Dänzer <michel@...nzer.net>
To:	Mayank Rungta <mr.mynk@...il.com>
Cc:	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	yakui.zhao@...el.com, "A.R Karthick" <a.r.karthick@...il.com>,
	karthick.linuxdreamer@...il.com
Subject: Re: [PATCH 2.6.38-10-generic] device driver: fix oops in radeon
 driver due to incorrect value from hardware

On Die, 2011-08-09 at 23:52 +0530, Mayank Rungta wrote: 
> Added a check for the radeon ring buffer write index in r600.c which 
> reads 0xffffffff on resume. This results in an Oops during 
> radeon_ring_write. Masking the value averts this.
> 
> This problem is not seen to be fixed in 3.0 r600.c as well.
> 
> Detailed analysis of the problem can be found at -
> 
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/820746/
> 
> ---
> 
> BUG: unable to handle kernel paging request at fa501ffc - Oops at 
> r600_cp_start+0x48/0x380 in r600_cp_resume+0x345/0x580 [radeon]
> 
> drivers/gpu/drm/radeon/r600.c
> 
> 
> 
> --- linux-2.6.38/drivers/gpu/drm/radeon/r600.c.orig    2011-08-05 
> 15:39:40.824612700 +0530
> +++ linux-2.6.38/drivers/gpu/drm/radeon/r600.c    2011-08-08 
> 05:29:21.744417857 +0530
> @@ -2218,6 +2218,8 @@ int r600_cp_resume(struct radeon_device
> 
>       rdev->cp.rptr = RREG32(CP_RB_RPTR);
>       rdev->cp.wptr = RREG32(CP_RB_WPTR);
> +    /* protect against crazy HW on resume */
> +    rdev->cp.wptr &= rdev->cp.ptr_mask;

The indentation of the lines you're adding doesn't match the surrounding
lines.


Although the same workaround is already in r100.c, I wonder if we
shouldn't rather try and eliminate all reads from the CP_RB_WPTR
register, at least other than for debugging purposes. Alex, what do you
think?

Otherwise, this should probably be added in evergreen.c as well.


>          Developer's Certificate of Origin 1.1
> 
>          [...]

No need to include all this text, just the *-by: tags are enough.


-- 
Earthling Michel Dänzer           |                   http://www.amd.com
Libre software enthusiast         |          Debian, X and DRI developer
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