[PATCH 1/1] drm/radeon: Fix Asus M2A-VM HDMI EDID error flooding problem

[Thomas Reim <reimth@googlemail.com>]

Some integrated ATI Radeon  chipset implementations
(e. g. Asus M2A-VM HDMI) indicate the availability
of a DDC even when there's no monitor connected.
In this case, drm_get_edid and drm_edid_block_valid
periodically dump data and kernel errors into system
log files and onto terminals, which lead to an unacceptable
system behaviour.

Tested since kernel 2.35 on Asus M2A-VM HDMI board

Signed-off-by: Thomas Reim <rdratlos@yahoo.co.uk>
---
 drivers/gpu/drm/radeon/radeon_connectors.c |   10 +++++
 drivers/gpu/drm/radeon/radeon_display.c    |   11 +++++
 drivers/gpu/drm/radeon/radeon_i2c.c        |   60 ++++++++++++++++++++++++++++
 drivers/gpu/drm/radeon/radeon_mode.h       |    1 +
 4 files changed, 82 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/radeon/radeon_connectors.c b/drivers/gpu/drm/radeon/radeon_connectors.c
index cbfca3a..7a76e45 100644
--- a/drivers/gpu/drm/radeon/radeon_connectors.c
+++ b/drivers/gpu/drm/radeon/radeon_connectors.c
@@ -828,6 +828,16 @@ radeon_dvi_detect(struct drm_connector *connector, bool force)
 
 	if (radeon_connector->ddc_bus)
 		dret = radeon_ddc_probe(radeon_connector);
+
+	/* Asus M2A-VM HDMI DDC quirk:
+	 * Some integrated ATI Radeon chipset implementations (e. g. Asus
+	 * M2A-VM HDMI) indicate the availability of a DDC even when there's
+	 * no monitor connected.The following check prevents drm_get_edid()
+	 * and drm_edid_block_valid() of periodically dumping data and kernel
+	 * errors into the logs and onto the terminal, which would lead to an
+	 * unacceptable system behaviour */
+	if (dret && connector->connector_type == DRM_MODE_CONNECTOR_HDMIA)
+		dret = radeon_ddc_edid_probe(radeon_connector);
 	if (dret) {
 		if (radeon_connector->edid) {
 			kfree(radeon_connector->edid);
diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
index 292f73f..550f143 100644
--- a/drivers/gpu/drm/radeon/radeon_display.c
+++ b/drivers/gpu/drm/radeon/radeon_display.c
@@ -715,6 +715,9 @@ static bool radeon_setup_enc_conn(struct drm_device *dev)
 	if (ret) {
 		radeon_setup_encoder_clones(dev);
 		radeon_print_display_setup(dev);
+		/* Is this really required here?
+		   Seems to just force drm to dump EDID errors
+		   to kernel logs */
 		list_for_each_entry(drm_connector, &dev->mode_config.connector_list, head)
 			radeon_ddc_dump(drm_connector);
 	}
@@ -777,8 +780,16 @@ static int radeon_ddc_dump(struct drm_connector *connector)
 	if (!radeon_connector->ddc_bus)
 		return -1;
 	edid = drm_get_edid(connector, &radeon_connector->ddc_bus->adapter);
+	/* Asus M2A-VM HDMI DDC quirk: Log EDID retrieval status here once,
+	 * instead of periodically dumping data and kernel errors into the
+	 * logs, if a monitor is not connected to HDMI */
 	if (edid) {
+		DRM_INFO("Radeon display connector %s: Found valid EDID",
+				drm_get_connector_name(connector));
 		kfree(edid);
+	} else {
+		DRM_INFO("Radeon display connector %s: No display connected or invalid EDID",
+				drm_get_connector_name(connector));
 	}
 	return ret;
 }
diff --git a/drivers/gpu/drm/radeon/radeon_i2c.c b/drivers/gpu/drm/radeon/radeon_i2c.c
index 781196d..1d6decd 100644
--- a/drivers/gpu/drm/radeon/radeon_i2c.c
+++ b/drivers/gpu/drm/radeon/radeon_i2c.c
@@ -63,6 +63,66 @@ bool radeon_ddc_probe(struct radeon_connector *radeon_connector)
 	return false;
 }
 
+/**
+ * Probe EDID information via I2C.
+ *
+ * \param adapter : i2c device adaptor
+ * \param buf     : EDID data buffer to be filled
+ * \param len     : EDID data buffer length
+ * \return 0 on success or -1 on failure.
+ *
+ * Try to fetch EDID information by calling i2c driver function and
+ * probe for EDID header information.
+ *
+ * Remark:
+ * This function has been added, because there are integrated ATI Radeon
+ * chipset implementations (e. g. Asus M2A-VM HDMI that indicate the
+ * availability of a DDC even when there's no monitor connected.
+ * In this case, drm_get_edid and drm_edid_block_valid periodically dump
+ * data and kernel errors into the logs and onto the terminal, which lead to
+ * an unacceptable system behaviour.
+ */
+bool radeon_ddc_edid_probe(struct radeon_connector *radeon_connector)
+{
+	u8 out_buf[] = { 0x0, 0x0};
+	u8 block[20];
+	int ret;
+	struct i2c_msg msgs[] = {
+		{
+			.addr	= 0x50,
+			.flags	= 0,
+			.len	= 1,
+			.buf	= out_buf,
+		}, {
+			.addr	= 0x50,
+			.flags	= I2C_M_RD,
+			.len	= 20,
+			.buf	= block,
+		}
+	};
+
+	ret = i2c_transfer(&radeon_connector->ddc_bus->adapter, msgs, 2);
+	if (ret == 2)
+		if ((block[0] == 0x00) &&
+		    (block[7] == 0x00) &&
+		    (block[1] == 0xff) &&
+		    (block[2] == 0xff) &&
+		    (block[3] == 0xff) &&
+		    (block[4] == 0xff) &&
+		    (block[5] == 0xff) &&
+		    (block[6] == 0xff))
+			/* EDID header starts with:
+			 * 0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x00;
+			 * seems to be an EDID */
+			if ((block[18] != 0x00) || (block[19] != 0x00))
+				/* EDID headers end with EDID version and
+				 * revision number: EDID version is not 0.0 =>
+				 * EDID should be available */
+				return true;
+	/* Couldn't find an accessible EDID on this connector. */
+	return false;
+}
+
 /* bit banging i2c */
 
 static void radeon_i2c_do_lock(struct radeon_i2c_chan *i2c, int lock_state)
diff --git a/drivers/gpu/drm/radeon/radeon_mode.h b/drivers/gpu/drm/radeon/radeon_mode.h
index 6df4e3c..14710fc 100644
--- a/drivers/gpu/drm/radeon/radeon_mode.h
+++ b/drivers/gpu/drm/radeon/radeon_mode.h
@@ -515,6 +515,7 @@ extern void radeon_i2c_put_byte(struct radeon_i2c_chan *i2c,
 extern void radeon_router_select_ddc_port(struct radeon_connector *radeon_connector);
 extern void radeon_router_select_cd_port(struct radeon_connector *radeon_connector);
 extern bool radeon_ddc_probe(struct radeon_connector *radeon_connector);
+extern bool radeon_ddc_edid_probe(struct radeon_connector *radeon_connector);
 extern int radeon_ddc_get_modes(struct radeon_connector *radeon_connector);
 
 extern struct drm_encoder *radeon_best_encoder(struct drm_connector *connector);
-- 
1.7.1