drm/i915: Add function to output Aksv over GMBUS

Once the Aksv is available in the PCH, we need to get it on the wire to
the receiver via DDC. The hardware doesn't allow us to read the value
directly, so we need to tell GMBUS to source the Aksv internally and
send it to the right offset on the receiver.

The way we do this is to initiate an indexed write where the index is
the Aksv register offset. We write dummy values to GMBUS3 as if we were
sending the key, and the hardware slips in the "real" values when it
goes out.

Changes in v2:
- None
Changes in v3:
- Uses new index write feature (Ville)
Changes in v4:
- None
Changes in v5:
- checkpatch whitespace fix
Changes in v6:
- None

Cc: Ville Syrjälä <[email protected]>
Reviewed-by: Daniel Vetter <[email protected]>
Signed-off-by: Sean Paul <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: atseanpaul

drivers/gpu/drm/i915/i915_drv.h

@@ -3644,6 +3644,7 @@ extern int intel_setup_gmbus(struct drm_i915_private *dev_priv);
 extern void intel_teardown_gmbus(struct drm_i915_private *dev_priv);
 extern bool intel_gmbus_is_valid_pin(struct drm_i915_private *dev_priv,
 				     unsigned int pin);
+extern int intel_gmbus_output_aksv(struct i2c_adapter *adapter);
 
 extern struct i2c_adapter *
 intel_gmbus_get_adapter(struct drm_i915_private *dev_priv, unsigned int pin);

drivers/gpu/drm/i915/i915_reg.h

@@ -3043,6 +3043,7 @@ enum i915_power_well_id {
 # define GPIO_DATA_PULLUP_DISABLE	(1 << 13)
 
 #define GMBUS0			_MMIO(dev_priv->gpio_mmio_base + 0x5100) /* clock/port select */
+#define   GMBUS_AKSV_SELECT	(1<<11)
 #define   GMBUS_RATE_100KHZ	(0<<8)
 #define   GMBUS_RATE_50KHZ	(1<<8)
 #define   GMBUS_RATE_400KHZ	(2<<8) /* reserved on Pineview */

drivers/gpu/drm/i915/intel_i2c.c

@@ -30,6 +30,7 @@
 #include <linux/i2c-algo-bit.h>
 #include <linux/export.h>
 #include <drm/drmP.h>
+#include <drm/drm_hdcp.h>
 #include "intel_drv.h"
 #include <drm/i915_drm.h>
 #include "i915_drv.h"
@@ -507,7 +508,8 @@ gmbus_index_xfer(struct drm_i915_private *dev_priv, struct i2c_msg *msgs)
 }
 
 static int
-do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
+do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num,
+	      u32 gmbus0_source)
 {
 	struct intel_gmbus *bus = container_of(adapter,
 					       struct intel_gmbus,
@@ -524,7 +526,7 @@ do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
 		pch_gmbus_clock_gating(dev_priv, false);
 
 retry:
-	I915_WRITE_FW(GMBUS0, bus->reg0);
+	I915_WRITE_FW(GMBUS0, gmbus0_source | bus->reg0);
 
 	for (; i < num; i += inc) {
 		inc = 1;
@@ -649,7 +651,7 @@ gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
 		if (ret < 0)
 			bus->force_bit &= ~GMBUS_FORCE_BIT_RETRY;
 	} else {
-		ret = do_gmbus_xfer(adapter, msgs, num);
+		ret = do_gmbus_xfer(adapter, msgs, num, 0);
 		if (ret == -EAGAIN)
 			bus->force_bit |= GMBUS_FORCE_BIT_RETRY;
 	}
@@ -659,6 +661,45 @@ gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
 	return ret;
 }
 
+int intel_gmbus_output_aksv(struct i2c_adapter *adapter)
+{
+	struct intel_gmbus *bus = container_of(adapter, struct intel_gmbus,
+					       adapter);
+	struct drm_i915_private *dev_priv = bus->dev_priv;
+	int ret;
+	u8 cmd = DRM_HDCP_DDC_AKSV;
+	u8 buf[DRM_HDCP_KSV_LEN] = { 0 };
+	struct i2c_msg msgs[] = {
+		{
+			.addr = DRM_HDCP_DDC_ADDR,
+			.flags = 0,
+			.len = sizeof(cmd),
+			.buf = &cmd,
+		},
+		{
+			.addr = DRM_HDCP_DDC_ADDR,
+			.flags = 0,
+			.len = sizeof(buf),
+			.buf = buf,
+		}
+	};
+
+	intel_display_power_get(dev_priv, POWER_DOMAIN_GMBUS);
+	mutex_lock(&dev_priv->gmbus_mutex);
+
+	/*
+	 * In order to output Aksv to the receiver, use an indexed write to
+	 * pass the i2c command, and tell GMBUS to use the HW-provided value
+	 * instead of sourcing GMBUS3 for the data.
+	 */
+	ret = do_gmbus_xfer(adapter, msgs, ARRAY_SIZE(msgs), GMBUS_AKSV_SELECT);
+
+	mutex_unlock(&dev_priv->gmbus_mutex);
+	intel_display_power_put(dev_priv, POWER_DOMAIN_GMBUS);
+
+	return ret;
+}
+
 static u32 gmbus_func(struct i2c_adapter *adapter)
 {
 	return i2c_bit_algo.functionality(adapter) &