drm/i915: Intercept Aksv writes in the aux hooks

Instead of hand rolling the transfer ourselves in the hdcp hook, inspect
aux messages and add the aksv flag in the aux transfer hook.

IIRC, this was the original implementation and folks wanted this hack to
be isolated to the hdcp code, which makes sense.

However in testing an LG monitor on my desk, I noticed it was passing
back a DEFER reply. This wasn't handled in our hand-rolled code and HDCP
auth was failing as a result. Instead of copy/pasting all of the retry
logic and delays from drm dp helpers, let's just use the helpers and hide
the aksv select as best as we can.
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ramalingam C <ramalingam.c@intel.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20191203173638.94919-3-sean@poorly.run #v1
Link: https://patchwork.freedesktop.org/patch/msgid/20191212190230.188505-5-sean@poorly.run #v2
Link: https://patchwork.freedesktop.org/patch/msgid/20200117193103.156821-5-sean@poorly.run #v3
Link: https://patchwork.freedesktop.org/patch/msgid/20200218220242.107265-5-sean@poorly.run #v4
Link: https://patchwork.freedesktop.org/patch/msgid/20200305201236.152307-5-sean@poorly.run #v5
Link: https://patchwork.freedesktop.org/patch/msgid/20200429195502.39919-5-sean@poorly.run #v6
Link: https://patchwork.freedesktop.org/patch/msgid/20200623155907.22961-5-sean@poorly.run #v7

Changes in v2:
-Remove 'generate' in intel_dp_aux_generate_xfer_flags, make arg const (Ville)
-Bundle Aksv if statement together (Ville)
-Rename 'txbuf' to 'aksv' (Ville)
Changes in v3:
-None
Changes in v4:
-None
Changes in v5:
-None
Changes in v6:
-None
Changes in v7:
-None
Changes in v8:
-None
Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200818153910.27894-5-sean@poorly.run

drivers/gpu/drm/i915/display/intel_dp.c

@@ -1563,6 +1563,20 @@ intel_dp_aux_header(u8 txbuf[HEADER_SIZE],
 	txbuf[3] = msg->size - 1;
 }
 
+static u32 intel_dp_aux_xfer_flags(const struct drm_dp_aux_msg *msg)
+{
+	/*
+	 * If we're trying to send the HDCP Aksv, we need to set a the Aksv
+	 * select bit to inform the hardware to send the Aksv after our header
+	 * since we can't access that data from software.
+	 */
+	if ((msg->request & ~DP_AUX_I2C_MOT) == DP_AUX_NATIVE_WRITE &&
+	    msg->address == DP_AUX_HDCP_AKSV)
+		return DP_AUX_CH_CTL_AUX_AKSV_SELECT;
+
+	return 0;
+}
+
 static ssize_t
 intel_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 {
@@ -1570,6 +1584,7 @@ intel_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
 	u8 txbuf[20], rxbuf[20];
 	size_t txsize, rxsize;
+	u32 flags = intel_dp_aux_xfer_flags(msg);
 	int ret;
 
 	intel_dp_aux_header(txbuf, msg);
@@ -1590,7 +1605,7 @@ intel_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 			memcpy(txbuf + HEADER_SIZE, msg->buffer, msg->size);
 
 		ret = intel_dp_aux_xfer(intel_dp, txbuf, txsize,
-					rxbuf, rxsize, 0);
+					rxbuf, rxsize, flags);
 		if (ret > 0) {
 			msg->reply = rxbuf[0] >> 4;
 
@@ -1613,7 +1628,7 @@ intel_dp_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
 			return -E2BIG;
 
 		ret = intel_dp_aux_xfer(intel_dp, txbuf, txsize,
-					rxbuf, rxsize, 0);
+					rxbuf, rxsize, flags);
 		if (ret > 0) {
 			msg->reply = rxbuf[0] >> 4;
 			/*
@@ -6416,15 +6431,8 @@ int intel_dp_hdcp_write_an_aksv(struct intel_digital_port *dig_port,
 				u8 *an)
 {
 	struct drm_i915_private *i915 = to_i915(dig_port->base.base.dev);
-	struct intel_dp *intel_dp = enc_to_intel_dp(to_intel_encoder(&dig_port->base.base));
-	static const struct drm_dp_aux_msg msg = {
-		.request = DP_AUX_NATIVE_WRITE,
-		.address = DP_AUX_HDCP_AKSV,
-		.size = DRM_HDCP_KSV_LEN,
-	};
-	u8 txbuf[HEADER_SIZE + DRM_HDCP_KSV_LEN] = {}, rxbuf[2], reply = 0;
+	u8 aksv[DRM_HDCP_KSV_LEN] = {};
 	ssize_t dpcd_ret;
-	int ret;
 
 	/* Output An first, that's easy */
 	dpcd_ret = drm_dp_dpcd_write(&dig_port->dp.aux, DP_AUX_HDCP_AN,
@@ -6437,31 +6445,19 @@ int intel_dp_hdcp_write_an_aksv(struct intel_digital_port *dig_port,
 	}
 
 	/*
-	 * Since Aksv is Oh-So-Secret, we can't access it in software. So in
-	 * order to get it on the wire, we need to create the AUX header as if
-	 * we were writing the data, and then tickle the hardware to output the
-	 * data once the header is sent out.
+	 * Since Aksv is Oh-So-Secret, we can't access it in software. So we
+	 * send an empty buffer of the correct length through the DP helpers. On
+	 * the other side, in the transfer hook, we'll generate a flag based on
+	 * the destination address which will tickle the hardware to output the
+	 * Aksv on our behalf after the header is sent.
 	 */
-	intel_dp_aux_header(txbuf, &msg);
-
-	ret = intel_dp_aux_xfer(intel_dp, txbuf, HEADER_SIZE + msg.size,
-				rxbuf, sizeof(rxbuf),
-				DP_AUX_CH_CTL_AUX_AKSV_SELECT);
-	if (ret < 0) {
-		drm_dbg_kms(&i915->drm,
-			    "Write Aksv over DP/AUX failed (%d)\n", ret);
-		return ret;
-	} else if (ret == 0) {
-		drm_dbg_kms(&i915->drm, "Aksv write over DP/AUX was empty\n");
-		return -EIO;
-	}
-
-	reply = (rxbuf[0] >> 4) & DP_AUX_NATIVE_REPLY_MASK;
-	if (reply != DP_AUX_NATIVE_REPLY_ACK) {
+	dpcd_ret = drm_dp_dpcd_write(&dig_port->dp.aux, DP_AUX_HDCP_AKSV,
+				     aksv, DRM_HDCP_KSV_LEN);
+	if (dpcd_ret != DRM_HDCP_KSV_LEN) {
 		drm_dbg_kms(&i915->drm,
-			    "Aksv write: no DP_AUX_NATIVE_REPLY_ACK %x\n",
-			    reply);
-		return -EIO;
+			    "Failed to write Aksv over DP/AUX (%zd)\n",
+			    dpcd_ret);
+		return dpcd_ret >= 0 ? -EIO : dpcd_ret;
 	}
 	return 0;
 }