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 265a0862a961ca850099732f90a116e3c8f53723..acb489ff3630bdcf9766d1103f2a240de25936b6 100644 (file)
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -254,6 +254,8 @@ drm_do_probe_ddc_edid(struct i2c_adapter *adapter, unsigned char *buf,
                      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 @@ drm_do_probe_ddc_edid(struct i2c_adapter *adapter, unsigned char *buf,
        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 @@ drm_do_probe_ddc_edid(struct i2c_adapter *adapter, unsigned char *buf,
                                .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)