drm/radeon: Extended DDC Probing for Connectors with Improperly Wired DDC Lines (here: Asus M2A-VM HDMI)

    Some integrated ATI Radeon chipset implementations with add-on HDMI card
    (e. g. Asus M2A-VM HDMI) indicate the availability of a DDC even
    when the add-on card is not plugged in or HDMI is disabled in BIOS setup.
    In this case, drm_get_edid() and drm_edid_block_valid() periodically
    dump data and kernel errors into system log files and onto terminals.
    For these connectors DDC probing is extended by a check for a correct
    EDID header. Only in case a valid EDID header is also found, the
    (HDMI or DVI) connector will be used by the Radeon driver. This prevents
    the kernel driver from useless flooding of logs and terminal sessions with
    EDID dumps and error messages.
    This patch adds a flag 'requires_extended_probe' to the radeon_connector
    structure. In function radeon_connector_needs_extended_probe() this flag
    can be set on a chipset family/vendor/connector type specific basis.
    In addition, function radeon_ddc_probe() has been adapted to perform
    extended DDC probing if required by the connector's flag.
    Requires function drm_edid_header_is_valid() in DRM module provided by
    [PATCH] drm: Separate EDID Header Check from EDID Block Check.

    Tested for kernel 2.6.35, 2.6.38 and 3.0 on Asus M2A-VM HDMI board

    BugLink: https://bugzilla.redhat.com/show_bug.cgi?id=668196
    BugLink: http://bugs.launchpad.net/bugs/7228066

Cc: <stable@kernel.org>
Signed-off-by: Thomas Reim <reimth@gmail.com>
Reviewed-by: Alex Deucher <alexdeucher@gmail.com>
Acked-by: Stephen Michaels <Stephen.Micheals@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 24 insertions, 8 deletions

diff --git a/drivers/gpu/drm/radeon/radeon_i2c.c b/drivers/gpu/drm/radeon/radeon_i2c.c
index 781196db792f..6c111c1fa3f9 100644
--- a/drivers/gpu/drm/radeon/radeon_i2c.c
+++ b/drivers/gpu/drm/radeon/radeon_i2c.c
@@ -32,17 +32,17 @@
  * radeon_ddc_probe
  *
  */
-bool radeon_ddc_probe(struct radeon_connector *radeon_connector)
+bool radeon_ddc_probe(struct radeon_connector *radeon_connector, bool requires_extended_probe)
 {
-	u8 out_buf[] = { 0x0, 0x0};
-	u8 buf[2];
+	u8 out = 0x0;
+	u8 buf[8];
 	int ret;
 	struct i2c_msg msgs[] = {
 		{
 			.addr = 0x50,
 			.flags = 0,
 			.len = 1,
-			.buf = out_buf,
+			.buf = &out,
 		},
 		{
 			.addr = 0x50,
@@ -52,15 +52,31 @@ bool radeon_ddc_probe(struct radeon_connector *radeon_connector)
 		}
 	};
 
+	/* Read 8 bytes from i2c for extended probe of EDID header */
+	if (requires_extended_probe)
+		msgs[1].len = 8;
+
 	/* on hw with routers, select right port */
 	if (radeon_connector->router.ddc_valid)
 		radeon_router_select_ddc_port(radeon_connector);
 
 	ret = i2c_transfer(&radeon_connector->ddc_bus->adapter, msgs, 2);
-	if (ret == 2)
-		return true;
-
-	return false;
+	if (ret != 2)
+		/* Couldn't find an accessible DDC on this connector */
+		return false;
+	if (requires_extended_probe) {
+		/* Probe also for valid EDID header
+		 * EDID header starts with:
+		 * 0x00,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x00.
+		 * Only the first 6 bytes must be valid as
+		 * drm_edid_block_valid() can fix the last 2 bytes */
+		if (drm_edid_header_is_valid(buf) < 6) {
+			/* Couldn't find an accessible EDID on this
+			 * connector */
+			return false;
+		}
+	}
+	return true;
 }
 
 /* bit banging i2c */