drm: edid: add support for E-DDC
The current logic for probing ddc is limited to
2 blocks (256 bytes), this patch adds support
for the 4 block (512) data.
To do this, a single 8-bit segment index is
passed to the display via the I2C address 30h.
Data from the selected segment is then immediately
read via the regular DDC2 address using a repeated
I2C 'START' signal.
Signed-off-by: Shirish S <s.shirish@samsung.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Ville Syrjala <ville.syrjala@linux.intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 265a086..acb489f 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -254,6 +254,8 @@
int block, int len)
{
unsigned char start = block * EDID_LENGTH;
+ unsigned char segment = block >> 1;
+ unsigned char xfers = segment ? 3 : 2;
int ret, retries = 5;
/* The core i2c driver will automatically retry the transfer if the
@@ -265,6 +267,11 @@
do {
struct i2c_msg msgs[] = {
{
+ .addr = DDC_SEGMENT_ADDR,
+ .flags = 0,
+ .len = 1,
+ .buf = &segment,
+ }, {
.addr = DDC_ADDR,
.flags = 0,
.len = 1,
@@ -276,15 +283,21 @@
.buf = buf,
}
};
- ret = i2c_transfer(adapter, msgs, 2);
+
+ /*
+ * Avoid sending the segment addr to not upset non-compliant ddc
+ * monitors.
+ */
+ ret = i2c_transfer(adapter, &msgs[3 - xfers], xfers);
+
if (ret == -ENXIO) {
DRM_DEBUG_KMS("drm: skipping non-existent adapter %s\n",
adapter->name);
break;
}
- } while (ret != 2 && --retries);
+ } while (ret != xfers && --retries);
- return ret == 2 ? 0 : -1;
+ return ret == xfers ? 0 : -1;
}
static bool drm_edid_is_zero(u8 *in_edid, int length)