[Intel-gfx] [PATCH] drm/i915/cnl: WA Display #1178 to fix some type C dongles

[Lucas De Marchi]

WA Display #1178 is meant to fix Aux channel voltage swing too low with
some type C dongles. Although it is for type C, HW engineers reported
that it can be applied to all external ports even if they are not going
to type C.

For CNL we apply the workaround every time Aux B, C and D are powering
up since they will lose the configuration when powered down.

Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
Cc: Arthur J Runyan <arthur.j.runyan at intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>
---

Since this is a workaround I think it would be desirable not to be
so intrusive. The simplest thing to do is to add the
IS_CANNONLAKE() and workaround as done here.

An alternative that may be more elegant (but also more intrusive) is to
declare a new ops for CNL for AUX B/C/D. Let me know what you think.

For the type-C dongles that I have here it worked both with and without
this patch, so bear in mind I couldn't actually reproduce the problem.

 drivers/gpu/drm/i915/i915_reg.h         | 11 +++++++++++
 drivers/gpu/drm/i915/intel_runtime_pm.c |  9 +++++++++
 2 files changed, 20 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
index 96c80fa0fcac..32064605f82d 100644
--- a/drivers/gpu/drm/i915/i915_reg.h
+++ b/drivers/gpu/drm/i915/i915_reg.h
@@ -8332,6 +8332,17 @@ enum skl_power_gate {
 #define  SKL_PW_TO_PG(pw)			((pw) - SKL_DISP_PW_1 + SKL_PG1)
 #define  SKL_FUSE_PG_DIST_STATUS(pg)		(1 << (27 - (pg)))
 
+#define _CNL_AUX_REG_IDX(pw)		((pw - 1) >> 4)
+#define _CNL_AUX_ANAOVRD1_B		0x162250
+#define _CNL_AUX_ANAOVRD1_C		0x162210
+#define _CNL_AUX_ANAOVRD1_D		0x1622D0
+#define CNL_AUX_ANAOVRD1(pw)		_MMIO(_PICK(_CNL_AUX_REG_IDX(pw), \
+						    _CNL_AUX_ANAOVRD1_B, \
+						    _CNL_AUX_ANAOVRD1_C, \
+						    _CNL_AUX_ANAOVRD1_D))
+#define   CNL_AUX_ANAOVRD1_ENABLE	(1<<16)
+#define   CNL_AUX_ANAOVRD1_LDO_BYPASS	(1<<23)
+
 /* Per-pipe DDI Function Control */
 #define _TRANS_DDI_FUNC_CTL_A		0x60400
 #define _TRANS_DDI_FUNC_CTL_B		0x61400
diff --git a/drivers/gpu/drm/i915/intel_runtime_pm.c b/drivers/gpu/drm/i915/intel_runtime_pm.c
index 8315499452dc..9bf200e4885d 100644
--- a/drivers/gpu/drm/i915/intel_runtime_pm.c
+++ b/drivers/gpu/drm/i915/intel_runtime_pm.c
@@ -388,6 +388,15 @@ static void hsw_power_well_enable(struct drm_i915_private *dev_priv,
 	I915_WRITE(HSW_PWR_WELL_CTL_DRIVER(id), val | HSW_PWR_WELL_CTL_REQ(id));
 	hsw_wait_for_power_well_enable(dev_priv, power_well);
 
+	/* WA Display #1178 */
+	if (IS_CANNONLAKE(dev_priv) &&
+	    (id == CNL_DISP_PW_AUX_B || id == CNL_DISP_PW_AUX_C ||
+	     id == CNL_DISP_PW_AUX_D)) {
+		val = I915_READ(CNL_AUX_ANAOVRD1(id));
+		val |= CNL_AUX_ANAOVRD1_ENABLE | CNL_AUX_ANAOVRD1_LDO_BYPASS;
+		I915_WRITE(CNL_AUX_ANAOVRD1(id), val);
+	}
+
 	if (wait_fuses)
 		gen9_wait_for_power_well_fuses(dev_priv, pg);
 
-- 
2.14.3