On Tue, Mar 15, 2011 at 7:04 AM, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote:
> 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@xxxxxxxxx>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Looks good.
Reviewed-by: Alex Deucher <alexdeucher@xxxxxxxxx>
> ---
>
> I was going to suggest tuning the i2c_adapter.retries of the affected
> components, but that only covers EGAIN and not EREMOTEIO/ETIMEDOUT that
> afflicts us. With the alteration to only retry the transfer of the
> affected block, this looks to be a reasonable idea and complements the
> logic to retry corrupted transfers.
> -Chris
>
> ---
> drivers/gpu/drm/drm_edid.c | 44 ++++++++++++++++++++++++++------------------
> 1 files changed, 26 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
> index a245d17..ddc3da9 100644
> --- a/drivers/gpu/drm/drm_edid.c
> +++ b/drivers/gpu/drm/drm_edid.c
> @@ -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 *
> --
> 1.7.2.3
>
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