On Wed, Jul 15, 2015 at 09:50:42AM +0100, Chris Wilson wrote:
> Since we may conceivably encounter situations where the upper part of the
> 64bit register changes between reads, for example when a timestamp
> counter overflows, change the WARN into a retry loop.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Michał Winiarski <michal.winiarski@xxxxxxxxx>
Michał, as you correctly predicted this WARN will be hit in the wild
after adjusting reg_read_ioctl(TIMESTAMP).
Anyone care to review this patch?
> ---
> drivers/gpu/drm/i915/i915_drv.h | 17 ++++++++---------
> 1 file changed, 8 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index ee53873ab252..cfddd69bd06c 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -3484,15 +3484,14 @@ 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 = I915_READ(upper_reg); \
> - u32 lower = I915_READ(lower_reg); \
> - u32 tmp = I915_READ(upper_reg); \
> - if (upper != tmp) { \
> - upper = tmp; \
> - lower = I915_READ(lower_reg); \
> - WARN_ON(I915_READ(upper_reg) != upper); \
> - } \
> - (u64)upper << 32 | lower; })
> + u32 upper, lower, tmp; \
> + tmp = I915_READ(upper_reg); \
> + do { \
> + upper = tmp; \
> + lower = I915_READ(lower_reg); \
> + tmp = I915_READ(upper_reg); \
> + } while (upper != tmp); \
> + (u64)upper << 32 | lower; })
>
> #define POSTING_READ(reg) (void)I915_READ_NOTRACE(reg)
> #define POSTING_READ16(reg) (void)I915_READ16_NOTRACE(reg)
--
Chris Wilson, Intel Open Source Technology Centre
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