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@xxxxxxxxxxx>
---
drivers/gpu/drm/drm_edid.c | 83 ++++++++++++++++++++++++++++++++-----------
1 files changed, 62 insertions(+), 21 deletions(-)
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index a8743c3..a10a130 100644
--- 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 short segFlags = segment ? 0 : I2C_M_IGNORE_NAK;
int ret, retries = 5;
/* The core i2c driver will automatically retry the transfer if the
@@ -262,29 +264,68 @@ drm_do_probe_ddc_edid(struct i2c_adapter *adapter, unsigned char *buf,
* generate spurious NAKs and timeouts. Retrying the transfer
* of the individual block a few times seems to overcome this.
*/
- do {
- struct i2c_msg msgs[] = {
- {
- .addr = DDC_ADDR,
- .flags = 0,
- .len = 1,
- .buf = &start,
- }, {
- .addr = DDC_ADDR,
- .flags = I2C_M_RD,
- .len = len,
- .buf = buf,
+ switch (segment) {
+ /* To reduce traffic on I2C, we request the i2c xfer
+ * for segment addr only if 4 block edid data is
+ * present.
+ * 0 : DDC
+ * 1 : E-DDC
+ */
+ case 0:
+ do {
+ struct i2c_msg msgs[] = {
+ {
+ .addr = DDC_ADDR,
+ .flags = 0,
+ .len = 1,
+ .buf = &start,
+ }, {
+ .addr = DDC_ADDR,
+ .flags = I2C_M_RD,
+ .len = len,
+ .buf = buf,
+ }
+ };
+ ret = i2c_transfer(adapter, msgs, 2);
+ if (ret == -ENXIO) {
+ DRM_DEBUG_KMS("drm: skipping non-existent adapter %s\n",
+ adapter->name);
+ break;
}
- };
- ret = i2c_transfer(adapter, msgs, 2);
- if (ret == -ENXIO) {
- DRM_DEBUG_KMS("drm: skipping non-existent adapter %s\n",
- adapter->name);
- break;
- }
- } while (ret != 2 && --retries);
+ } while (ret != 2 && --retries);
+
+ return ret == 2 ? 0 : -1;
+ case 1:
+ do {
+ struct i2c_msg msgs[] = {
+ { /*set segment pointer */
+ .addr = DDC_SEGMENT_ADDR,
+ .flags = segFlags,
+ .len = 1,
+ .buf = &segment,
+ }, { /*set offset */
+ .addr = DDC_ADDR,
+ .flags = 0,
+ .len = 1,
+ .buf = &start,
+ }, { /*set data */
+ .addr = DDC_ADDR,
+ .flags = I2C_M_RD,
+ .len = len,
+ .buf = buf,
+ }
+ };
+ ret = i2c_transfer(adapter, msgs, 3);
+ if (ret == -ENXIO) {
+ DRM_DEBUG_KMS("drm: skipping non-existent adapter %s\n",
+ adapter->name);
+ break;
+ }
+ } while (ret != 3 && --retries);
- return ret == 2 ? 0 : -1;
+ return ret == 3 ? 0 : -1;
+ }
+ return -1;
}
static bool drm_edid_is_zero(u8 *in_edid, int length)
--
1.7.0.4
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