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

[Alex Deucher]

2011/8/10 Michel Dänzer <michel at daenzer.net>:
> 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?

Either this or reset the registers to 0 or a saved value on resume
rather than reading from them.

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

Yes, and ni.c as well.

Alex

>
>>          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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