drm/i915: BXT DDI PHY sequence BUN

According to the BSpec update, bit 7 of PORT_CL1CM_DW0 register needs to be
checked to ensure that the register is in accessible state.
Also, based on a BSpec update, changing the timeout value to
check iphypwrgood, from 10ms to wait for up to 100us.

v2: [Ville] use wait_for_us instead of the atomic call.
v3: [Jani/Imre] read register only once
Signed-off-by: Vandana Kannan <vandana.kannan@intel.com>
Reported-by: Philippe Lecluse <Philippe.Lecluse@intel.com>
Cc: Deak, Imre <imre.deak@intel.com>
Cc: Nikula, Jani <jani.nikula@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1459446354-19012-1-git-send-email-vandana.kannan@intel.com

drivers/gpu/drm/i915/i915_reg.h

@@ -1324,6 +1324,7 @@ enum skl_disp_power_wells {
 #define _PORT_CL1CM_DW0_A		0x162000
 #define _PORT_CL1CM_DW0_BC		0x6C000
 #define   PHY_POWER_GOOD		(1 << 16)
+#define   PHY_RESERVED			(1 << 7)
 #define BXT_PORT_CL1CM_DW0(phy)		_BXT_PHY((phy), _PORT_CL1CM_DW0_BC, \
 							_PORT_CL1CM_DW0_A)
 

drivers/gpu/drm/i915/intel_ddi.c

@@ -1732,9 +1732,18 @@ static void broxton_phy_init(struct drm_i915_private *dev_priv,
 	val |= GT_DISPLAY_POWER_ON(phy);
 	I915_WRITE(BXT_P_CR_GT_DISP_PWRON, val);
 
-	/* Considering 10ms timeout until BSpec is updated */
-	if (wait_for(I915_READ(BXT_PORT_CL1CM_DW0(phy)) & PHY_POWER_GOOD, 10))
+	/*
+	 * The PHY registers start out inaccessible and respond to reads with
+	 * all 1s.  Eventually they become accessible as they power up, then
+	 * the reserved bit will give the default 0.  Poll on the reserved bit
+	 * becoming 0 to find when the PHY is accessible.
+	 * HW team confirmed that the time to reach phypowergood status is
+	 * anywhere between 50 us and 100us.
+	 */
+	if (wait_for_us(((I915_READ(BXT_PORT_CL1CM_DW0(phy)) &
+		(PHY_RESERVED | PHY_POWER_GOOD)) == PHY_POWER_GOOD), 100)) {
 		DRM_ERROR("timeout during PHY%d power on\n", phy);
+	}
 
 	for (port =  (phy == DPIO_PHY0 ? PORT_B : PORT_A);
 	     port <= (phy == DPIO_PHY0 ? PORT_C : PORT_A); port++) {