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

[Mayank Rungta <mr.mynk@gmail.com>]

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;

      r600_cp_start(rdev);
      rdev->cp.ready = true;


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     Signed-off-by: A R Karthick <a.r.karthick@gmail.com>

     Reported-by: Mayank Rungta <mr.mynk@gmail.com>

     Tested-by: Mayank Rungta <mr.mynk@gmail.com>