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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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40
drivers/gpu/drm/drm_edid.c
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@ -230,24 +230,32 @@ drm_do_probe_ddc_edid(struct i2c_adapter *adapter, unsigned char *buf,
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 *