[Intel-gfx] [PATCH 2/5] drm/i915: PSR: Fix DP_PSR_NO_TRAIN_ON_EXIT logic

[R, Durgadoss]

>-----Original Message-----
>From: Vivi, Rodrigo
>Sent: Friday, April 10, 2015 11:45 PM
>To: intel-gfx at lists.freedesktop.org
>Cc: Vivi, Rodrigo; R, Durgadoss; Runyan, Arthur J
>Subject: [PATCH 2/5] drm/i915: PSR: Fix DP_PSR_NO_TRAIN_ON_EXIT logic
>
>Since the beginning there is a missunderstanding on the meaning of this
>dpcd bit.
>This bit shouldn't indicate whether to use link standby or not, but just
>be used to configure TP1, TP2 and TP3 times and tell hw aux should be skiped
>since HW is the responsible one.
>
>Even with help of frontbuffer tracking, HW is still fully responsible for
>PSR exit logic with/without DP training.
>
>DP_PSR_NO_TRAIN_ON_EXIT means the source doesn't need to do the training, but
>it doesn't tell to avoid TP patterns, so we will send minimal TP1 and avoid
>TP2. It also means that sink itself can take up to 5 idle frames for training.
>6 in our case since we might be off by 1. So we also increment idle_frames by 4
>here.
>
>v2: Fix and improve commit message (Durga).
>v3: Use minimal TP1 time avoiding TP2 and increase idle frame.
>
>Cc: Durgadoss R <durgadoss.r at intel.com>
>Cc: Arthur Runyan <arthur.j.runyan at intel.com>
>Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
>---
> drivers/gpu/drm/i915/intel_psr.c | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
>
>diff --git a/drivers/gpu/drm/i915/intel_psr.c b/drivers/gpu/drm/i915/intel_psr.c
>index db95b39..0e3b652 100644
>--- a/drivers/gpu/drm/i915/intel_psr.c
>+++ b/drivers/gpu/drm/i915/intel_psr.c
>@@ -264,11 +264,17 @@ static void hsw_psr_enable_source(struct intel_dp *intel_dp)
> 	uint32_t val = 0x0;
> 	const uint32_t link_entry_time = EDP_PSR_MIN_LINK_ENTRY_TIME_8_LINES;
>
>-	if (dev_priv->psr.link_standby) {
>+	if (dev_priv->psr.link_standby)
> 		val |= EDP_PSR_LINK_STANDBY;
>+
>+	if (intel_dp->psr_dpcd[1] & DP_PSR_NO_TRAIN_ON_EXIT) {
>+		/* It doesn't mean we shouldn't send TPS patters, so let's
>+		   send the minimal TP1 possible and skip TP2. */

We can fix the multi-line comment style though,

Reviewed-by: Durgadoss R <durgadoss.r at intel.com>

Thanks,
Durga

>+		val |= EDP_PSR_TP1_TIME_100us;
> 		val |= EDP_PSR_TP2_TP3_TIME_0us;
>-		val |= EDP_PSR_TP1_TIME_0us;
> 		val |= EDP_PSR_SKIP_AUX_EXIT;
>+		/* Sink should be able to train with the 5 or 6 idle patterns */
>+		idle_frames += 4;
> 	}
>
> 	I915_WRITE(EDP_PSR_CTL(dev), val |
>@@ -381,8 +387,7 @@ void intel_psr_enable(struct intel_dp *intel_dp)
> 	/* First we check VBT, but we must respect sink and source
> 	 * known restrictions */
> 	dev_priv->psr.link_standby = dev_priv->vbt.psr.full_link;
>-	if ((intel_dp->psr_dpcd[1] & DP_PSR_NO_TRAIN_ON_EXIT) ||
>-	    (IS_BROADWELL(dev) && intel_dig_port->port != PORT_A))
>+	if (IS_BROADWELL(dev) && intel_dig_port->port != PORT_A)
> 		dev_priv->psr.link_standby = true;
>
> 	dev_priv->psr.busy_frontbuffer_bits = 0;
>--
>2.1.0