drm: Retry i2c transfer of EDID block after failure
Usually EDID retrieval is fine. However, sometimes, especially when the
machine is loaded, it fails, but succeeds after a few retries.
Based on a patch by Michael Buesch.
Reported-by: Michael Buesch <mb@bu3sch.de>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Alex Deucher <alexdeucher@gmail.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 af60d9b..9c595e3 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -230,24 +230,32 @@
int block, int len)
{
unsigned char start = block * EDID_LENGTH;
- struct i2c_msg msgs[] = {
- {
- .addr = DDC_ADDR,
- .flags = 0,
- .len = 1,
- .buf = &start,
- }, {
- .addr = DDC_ADDR,
- .flags = I2C_M_RD,
- .len = len,
- .buf = buf,
- }
- };
+ int ret, retries = 5;
- if (i2c_transfer(adapter, msgs, 2) == 2)
- return 0;
+ /* The core i2c driver will automatically retry the transfer if the
+ * adapter reports EAGAIN. However, we find that bit-banging transfers
+ * are susceptible to errors under a heavily loaded machine and
+ * 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,
+ }
+ };
+ ret = i2c_transfer(adapter, msgs, 2);
+ } while (ret != 2 && --retries);
- return -1;
+ return ret == 2 ? 0 : -1;
}
static u8 *