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

Daniel Vetter
2013-09-20T21:53:20Z

On Fri, Sep 20, 2013 at 01:56:20PM -0700, Todd Previte wrote:
> 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>>

Your mailer sends out html+plaintext multipart mails and in the plaintext
section your r-b tags look rather funny. Can you please fix that?

Thanks, Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch