[PATCH v4 02/15] drm/xe: Mimic i915 behavior for non-sleeping MMIO wait

[Gustavo Sousa]

In upcoming display changes, we will modify the DMC wakelock MMIO
waiting code to choose a non-sleeping variant implementation, because
the wakelock is also taking in atomic context.

While xe provides an explicit parameter (namely "atomic") to prevent
xe_mmio_wait32() from sleeping, i915 does not and implements that
behavior when slow_timeout_ms is zero.

So, for now, let's mimic what i915 does to allow for display to use
non-sleeping MMIO wait. In the future, we should come up with a better
and explicit interface for this behavior in i915, at least while display
code is not an independent entity with proper interfaces between xe and
i915.

v2:
  - Make the tone in comment the comment added in
    __intel_wait_for_register() more explanatory than a FIXME-like text.
    (Luca)

Reviewed-by: Luca Coelho <luciano.coelho at intel.com>
Signed-off-by: Gustavo Sousa <gustavo.sousa at intel.com>
---
 drivers/gpu/drm/xe/compat-i915-headers/intel_uncore.h | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xe/compat-i915-headers/intel_uncore.h b/drivers/gpu/drm/xe/compat-i915-headers/intel_uncore.h
index 0382beb4035b..686c39f320e4 100644
--- a/drivers/gpu/drm/xe/compat-i915-headers/intel_uncore.h
+++ b/drivers/gpu/drm/xe/compat-i915-headers/intel_uncore.h
@@ -117,10 +117,19 @@ __intel_wait_for_register(struct intel_uncore *uncore, i915_reg_t i915_reg,
 			  unsigned int slow_timeout_ms, u32 *out_value)
 {
 	struct xe_reg reg = XE_REG(i915_mmio_reg_offset(i915_reg));
+	bool atomic;
+
+	/*
+	 * Replicate the behavior from i915 here, in which sleep is not
+	 * performed if slow_timeout_ms == 0. This is necessary because
+	 * of some paths in display code where waits are done in atomic
+	 * context.
+	 */
+	atomic = !slow_timeout_ms && fast_timeout_us > 0;
 
 	return xe_mmio_wait32(__compat_uncore_to_mmio(uncore), reg, mask, value,
 			      fast_timeout_us + 1000 * slow_timeout_ms,
-			      out_value, false);
+			      out_value, atomic);
 }
 
 static inline u32 intel_uncore_read_fw(struct intel_uncore *uncore,
-- 
2.47.0