[PATCH v7 1/2] drm/i915/psr: Lockless version of psr_wait_for_idle

[PATCH v7 1/2] drm/i915/psr: Lockless version of psr_wait_for_idle

[Tarun Vyas]

This is a lockless version of the exisiting psr_wait_for_idle().
We want to wait for PSR to idle out inside intel_pipe_update_start.
At the time of a pipe update, we should never race with any psr
enable or disable code, which is a part of crtc enable/disable.
The follow up patch will use this lockless wait inside pipe_update_
start to wait for PSR to idle out before checking for vblank evasion.
We need to keep the wait in pipe_update_start to as less as it can be.
So,we can live and flourish w/o taking any psr locks at all.

Even if psr is never enabled, psr2_enabled will be false and this
function will wait for PSR1 to idle out, which should just return
immediately, so a very short (~1-2 usec) wait for cases where PSR
is disabled.

v2: Add comment to explain the 25msec timeout (DK)

v3: Rename psr_wait_for_idle to __psr_wait_for_idle_locked to avoid
    naming conflicts and propagate err (if any) to the caller (Chris)

v5: Form a series with the next patch

v7: Better explain the need for lockless wait and increase the max
    timeout to handle refresh rates < 60 Hz (Daniel Vetter)

Signed-off-by: Tarun Vyas <tarun.vyas@intel.com>
---
 drivers/gpu/drm/i915/intel_drv.h |  1 +
 drivers/gpu/drm/i915/intel_psr.c | 36 ++++++++++++++++++++++++++++++++++--
 2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 578346b8d7e2..9cb2b8afdd3e 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -1920,6 +1920,7 @@ void intel_psr_compute_config(struct intel_dp *intel_dp,
 			      struct intel_crtc_state *crtc_state);
 void intel_psr_irq_control(struct drm_i915_private *dev_priv, bool debug);
 void intel_psr_irq_handler(struct drm_i915_private *dev_priv, u32 psr_iir);
+int intel_psr_wait_for_idle(struct drm_i915_private *dev_priv);
 
 /* intel_runtime_pm.c */
 int intel_power_domains_init(struct drm_i915_private *);
diff --git a/drivers/gpu/drm/i915/intel_psr.c b/drivers/gpu/drm/i915/intel_psr.c
index aea81ace854b..d11fd8a01d98 100644
--- a/drivers/gpu/drm/i915/intel_psr.c
+++ b/drivers/gpu/drm/i915/intel_psr.c
@@ -757,7 +757,39 @@ void intel_psr_disable(struct intel_dp *intel_dp,
 	cancel_work_sync(&dev_priv->psr.work);
 }
 
-static bool psr_wait_for_idle(struct drm_i915_private *dev_priv)
+int intel_psr_wait_for_idle(struct drm_i915_private *dev_priv)
+{
+	i915_reg_t reg;
+	u32 mask;
+
+	/*
+	 * The sole user right now is intel_pipe_update_start(),
+	 * which won't race with psr_enable/disable, which is
+	 * where psr2_enabled is written to. So, we don't need
+	 * to acquire the psr.lock. More importantly, we want the
+	 * latency inside intel_pipe_update_start() to be as low
+	 * as possible, so no need to acquire psr.lock when it is
+	 * not needed and will induce latencies in the atomic
+	 * update path.
+	 */
+	if (dev_priv->psr.psr2_enabled) {
+		reg = EDP_PSR2_STATUS;
+		mask = EDP_PSR2_STATUS_STATE_MASK;
+	} else {
+		reg = EDP_PSR_STATUS;
+		mask = EDP_PSR_STATUS_STATE_MASK;
+	}
+
+	/*
+	 * Max time for PSR to idle = Inverse of the refresh rate +
+	 * 6 ms of exit training time + 1.5 ms of aux channel
+	 * handshake. 50 msec is defesive enough to cover everything.
+	 */
+	return intel_wait_for_register(dev_priv, reg, mask,
+				       EDP_PSR_STATUS_STATE_IDLE, 50);
+}
+
+static bool __psr_wait_for_idle_locked(struct drm_i915_private *dev_priv)
 {
 	struct intel_dp *intel_dp;
 	i915_reg_t reg;
@@ -803,7 +835,7 @@ static void intel_psr_work(struct work_struct *work)
 	 * PSR might take some time to get fully disabled
 	 * and be ready for re-enable.
 	 */
-	if (!psr_wait_for_idle(dev_priv))
+	if (!__psr_wait_for_idle_locked(dev_priv))
 		goto unlock;
 
 	/*
-- 
2.13.5

_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/intel-gfx

[PATCH v7 2/2] drm/i915: Wait for PSR exit before checking for vblank evasion

[Tarun Vyas]

The PIPEDSL freezes on PSR entry and if PSR hasn't fully exited, then
the pipe_update_start call schedules itself out to check back later.

On ChromeOS-4.4 kernel, which is fairly up-to-date w.r.t drm/i915 but
lags w.r.t core kernel code, hot plugging an external display triggers
tons of "potential atomic update errors" in the dmesg, on *pipe A*. A
closer analysis reveals that we try to read the scanline 3 times and
eventually timeout, b/c PSR hasn't exited fully leading to a PIPEDSL
stuck @ 1599. This issue is not seen on upstream kernels, b/c for *some*
reason we loop inside intel_pipe_update start for ~2+ msec which in this
case is more than enough to exit PSR fully, hence an *unstuck* PIPEDSL
counter, hence no error. On the other hand, the ChromeOS kernel spends
~1.1 msec looping inside intel_pipe_update_start and hence errors out
b/c the source is still in PSR.

Regardless, we should wait for PSR exit (if PSR is disabled, we incur
a ~1-2 usec penalty) before reading the PIPEDSL, b/c if we haven't
fully exited PSR, then checking for vblank evasion isn't actually
applicable.

v4: Comment explaining psr_wait after enabling VBL interrupts (DK)

v5: CAN_PSR() to handle platforms that don't support PSR.

v6: Handle local_irq_disable on early return (Chris)

Signed-off-by: Tarun Vyas <tarun.vyas@intel.com>
---
 drivers/gpu/drm/i915/intel_sprite.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_sprite.c b/drivers/gpu/drm/i915/intel_sprite.c
index 344c0e709b19..4990d6e84ddf 100644
--- a/drivers/gpu/drm/i915/intel_sprite.c
+++ b/drivers/gpu/drm/i915/intel_sprite.c
@@ -107,13 +107,21 @@ void intel_pipe_update_start(const struct intel_crtc_state *new_crtc_state)
 						      VBLANK_EVASION_TIME_US);
 	max = vblank_start - 1;
 
-	local_irq_disable();
-
 	if (min <= 0 || max <= 0)
-		return;
+		goto irq_disable;
 
 	if (WARN_ON(drm_crtc_vblank_get(&crtc->base)))
-		return;
+		goto irq_disable;
+
+	/*
+	 * Wait for psr to idle out after enabling the VBL interrupts
+	 * VBL interrupts will start the PSR exit and prevent a PSR
+	 * re-entry as well.
+	 */
+	if (CAN_PSR(dev_priv) && intel_psr_wait_for_idle(dev_priv))
+		DRM_ERROR("PSR idle timed out, atomic update may fail\n");
+
+	local_irq_disable();
 
 	crtc->debug.min_vbl = min;
 	crtc->debug.max_vbl = max;
@@ -171,6 +179,10 @@ void intel_pipe_update_start(const struct intel_crtc_state *new_crtc_state)
 	crtc->debug.start_vbl_count = intel_crtc_get_vblank_counter(crtc);
 
 	trace_i915_pipe_update_vblank_evaded(crtc);
+	return;
+
+irq_disable:
+	local_irq_disable();
 }
 
 /**
-- 
2.13.5

_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/intel-gfx

✗ Fi.CI.BAT: failure for series starting with [v7,1/2] drm/i915/psr: Lockless version of psr_wait_for_idle

[Patchwork]

== Series Details ==

Series: series starting with [v7,1/2] drm/i915/psr: Lockless version of psr_wait_for_idle
URL   : https://patchwork.freedesktop.org/series/45521/
State : failure

== Summary ==

Applying: drm/i915/psr: Lockless version of psr_wait_for_idle
Using index info to reconstruct a base tree...
M	drivers/gpu/drm/i915/intel_drv.h
M	drivers/gpu/drm/i915/intel_psr.c
Falling back to patching base and 3-way merge...
Auto-merging drivers/gpu/drm/i915/intel_psr.c
Auto-merging drivers/gpu/drm/i915/intel_drv.h
CONFLICT (content): Merge conflict in drivers/gpu/drm/i915/intel_drv.h
error: Failed to merge in the changes.
Patch failed at 0001 drm/i915/psr: Lockless version of psr_wait_for_idle
Use 'git am --show-current-patch' to see the failed patch
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/intel-gfx