From: Chris Wilson Date: Tue, 8 Sep 2015 13:17:13 +0000 (+0100) Subject: drm/i915: Limit the number of loops for reading a split 64bit register X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=acd29f7b22262d9e848393b9b6ae13eb42d22514;p=linux-beck.git drm/i915: Limit the number of loops for reading a split 64bit register 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 hardware 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. v2: Use the most recent values when erring out on an unstable register. Reported-by: russianneuromancer@ya.ru Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91906 Signed-off-by: Chris Wilson Cc: Michał Winiarski Cc: Daniel Vetter Cc: Jani Nikula Cc: stable@vger.kernel.org Reviewed-by: Daniel Vetter Signed-off-by: Jani Nikula --- diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h index e304d4e5ae0c..522da7b12a88 100644 --- a/drivers/gpu/drm/i915/i915_drv.h +++ b/drivers/gpu/drm/i915/i915_drv.h @@ -3383,13 +3383,13 @@ 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; \ - tmp = I915_READ(upper_reg); \ + u32 upper, lower, old_upper, loop = 0; \ + upper = I915_READ(upper_reg); \ do { \ - upper = tmp; \ + old_upper = upper; \ lower = I915_READ(lower_reg); \ - tmp = I915_READ(upper_reg); \ - } while (upper != tmp); \ + upper = I915_READ(upper_reg); \ + } while (upper != old_upper && loop++ < 2); \ (u64)upper << 32 | lower; }) #define POSTING_READ(reg) (void)I915_READ_NOTRACE(reg)