From acd29f7b22262d9e848393b9b6ae13eb42d22514 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Tue, 8 Sep 2015 14:17:13 +0100 Subject: [PATCH] drm/i915: Limit the number of loops for reading a split 64bit register MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 --- drivers/gpu/drm/i915/i915_drv.h | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h index e304d4e..522da7b 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) -- 2.7.4