Re: [PATCH 2/4] drm/i915/dp: increase i2c-over-aux retry interval on AUX DEFER

Todd Previte
2013-09-20T20:56:23Z

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On 09/20/2013 06:42 AM, Jani Nikula wrote:
> There is no clear cut rules or specs for the retry interval, as there
> are many factors that affect overall response time. Increase the
> interval, and even more so on branch devices which may have limited i2c
> bit rates.
>
> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> ---
> drivers/gpu/drm/i915/intel_dp.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 6626514..3afbea9 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -678,7 +678,18 @@ intel_dp_i2c_aux_ch(struct i2c_adapter *adapter, int mode,
> DRM_DEBUG_KMS("aux_ch native nack\n");
> return -EREMOTEIO;
> case AUX_NATIVE_REPLY_DEFER:
> - udelay(100);
> + /*
> + * For now, just give more slack to branch devices. We
> + * could check the DPCD for I2C bit rate capabilities,
> + * and if available, adjust the interval. We could also
> + * be more careful with DP-to-Legacy adapters where a
> + * long legacy cable may force very low I2C bit rates.
> + */
> + if (intel_dp->dpcd[DP_DOWNSTREAMPORT_PRESENT] &
> + DP_DWN_STRM_PORT_PRESENT)
> + usleep_range(500, 600);
> + else
> + usleep_range(300, 400);
> continue;
> default:
> DRM_ERROR("aux_ch invalid native reply 0x%02x\n",

Those look like reasonable values to me.

[Reviewed-by]: Todd Previte <tprevite@gmail.com
<mailto:tprevite@gmail.com>>

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