On Mon, Apr 10, 2017 at 04:55:31PM +0100, Chris Wilson wrote:
> We acquire the forcewake and use I915_READ_FW instead for the atomic
> wait within intel_uncore_wait_for_register. However, this still leaves
> us vulnerable to concurrent mmio access to the register, which can cause
> system hangs on gen7. The protection is to acquire uncore.lock around
> each register, so lets add it back.
>
> v2: Wrap __intel_wait_for_register_fw() to re-use its atomic wait_for
> loop and spare adding another for ourselves.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Michal Wajdeczko <michal.wajdeczko@xxxxxxxxx>
> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/intel_uncore.c | 14 ++++++++++----
> 1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index 53c8457869f6..01cea3b7a704 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -1661,14 +1661,20 @@ int intel_wait_for_register(struct drm_i915_private *dev_priv,
> u32 value,
> unsigned int timeout_ms)
> {
> -
> unsigned fw =
> intel_uncore_forcewake_for_reg(dev_priv, reg, FW_REG_READ);
> int ret;
>
> - intel_uncore_forcewake_get(dev_priv, fw);
> - ret = wait_for_us((I915_READ_FW(reg) & mask) == value, 2);
> - intel_uncore_forcewake_put(dev_priv, fw);
> + spin_lock_irq(&dev_priv->uncore.lock);
> + intel_uncore_forcewake_get__locked(dev_priv, fw);
> +
> + ret = __intel_wait_for_register_fw(dev_priv,
> + reg, mask, value,
> + 2, 0, NULL);
> +
> + intel_uncore_forcewake_put__locked(dev_priv, fw);
> + spin_unlock_irq(&dev_priv->uncore.lock);
Hmm, shouldn't we use spin_lock_irqsave/spin_unlock_irqrestore here?
Like in GEN6_READ_HEADER/GEN6_READ_FOOTER.
-Michal
> +
> if (ret)
> ret = wait_for((I915_READ_NOTRACE(reg) & mask) == value,
> timeout_ms);
> --
> 2.11.0
>
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