On Tue, Sep 08, 2015 at 08:51:50AM +0100, Chris Wilson wrote: > On Tue, Sep 08, 2015 at 08:24:19AM +0100, Chris Wilson wrote: > > In I915_READ64_2x32 we attempt to read a 64bit register using 2 32bit > > reads. Due to the nature of the registers we try to read in this manner, > > they may increment between the two instruction (e.g. a timestamp > > counter). To keep the result accurate, we repeat the read if we detect > > an overflow (i.e. the upper value varies). However, some harware is just > > plain flaky and may endless loop as the the upper 32bits are not stable. > > Just give up after a couple of tries and report whatever we read last. > > > > Reported-by: [email protected] > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91906 > > Signed-off-by: Chris Wilson <[email protected]> > > Cc: Michał Winiarski <[email protected]> > > Cc: Daniel Vetter <[email protected]> > > Cc: [email protected] > > --- > > drivers/gpu/drm/i915/i915_drv.h | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/gpu/drm/i915/i915_drv.h > > b/drivers/gpu/drm/i915/i915_drv.h > > index 12870073d58f..8943dcb724a8 100644 > > --- a/drivers/gpu/drm/i915/i915_drv.h > > +++ b/drivers/gpu/drm/i915/i915_drv.h > > @@ -3402,13 +3402,13 @@ int intel_freq_opcode(struct drm_i915_private > > *dev_priv, int val); > > #define I915_READ64(reg) dev_priv->uncore.funcs.mmio_readq(dev_priv, > > (reg), true) > > > > #define I915_READ64_2x32(lower_reg, upper_reg) ({ \ > > - u32 upper, lower, tmp; \ > > + u32 upper, lower, tmp, loop = 0; \ > > tmp = I915_READ(upper_reg); \ > > do { \ > > upper = tmp; \ > > lower = I915_READ(lower_reg); \ > > tmp = I915_READ(upper_reg); \ > > - } while (upper != tmp); \ > > + } while (upper != tmp && loop++ != 2); \ > > Maybe "loop++ < 2" for one more character of clarity.
Yeah s/!=/</ is a bit clearer. With that Reviewed-by: Daniel Vetter <[email protected]> -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
