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drm: Retry i2c transfer of EDID block after failure

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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>
This commit is contained in:
Chris Wilson
2011-03-15 11:04:41 +00:00
committed by Dave Airlie
parent 942b0e95c3
commit 4819d2e431
1 changed files with 24 additions and 16 deletions
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16
drivers/gpu/drm/drm_edid.c
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@@ -230,6 +230,15 @@ drm_do_probe_ddc_edid(struct i2c_adapter *adapter, unsigned char *buf,
int block, int len) int block, int len)
{ {
unsigned char start = block * EDID_LENGTH; unsigned char start = block * EDID_LENGTH;
int ret, retries = 5;
/* 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[] = { struct i2c_msg msgs[] = {
{ {
.addr = DDC_ADDR, .addr = DDC_ADDR,
@@ -243,11 +252,10 @@ drm_do_probe_ddc_edid(struct i2c_adapter *adapter, unsigned char *buf,
.buf = buf, .buf = buf,
} }
}; };
ret = i2c_transfer(adapter, msgs, 2);
} while (ret != 2 && --retries);
if (i2c_transfer(adapter, msgs, 2) == 2) return ret == 2 ? 0 : -1;
return 0;
return -1;
} }
static u8 * static u8 *