On Thu, 21 May 2015, Todd Previte <tprevite@xxxxxxxxx> wrote: > Passive DP->DVI/HDMI dongles show up to the system as HDMI devices, as they > do not have a sink device in them to respond to any AUX traffic. When > probing these dongles over the DDC, sometimes they will NAK the first attempt > even though the transaction is valid and they support the DDC protocol. The > retry loop inside of drm_do_probe_ddc_edid() would normally catch this case > and try the transaction again, resulting in success. > > That, however, was thwarted by the fix for fdo.org bug #41059. The patch is: > commit 9292f37e1f5c79400254dca46f83313488093825 > Author: Eugeni Dodonov <eugeni.dodonov@xxxxxxxxx> > Date: Thu Jan 5 09:34:28 2012 -0200 > > drm: give up on edid retries when i2c bus is not responding Some extra background: That commit refers to the i2c bit banging code, while i915 now prefers gmbus, and only falls back to big banging on certain failures. (See gmbux_xfer() in i915/intel_i2c.c). This means that in most cases i915 is no longer susceptible to the 5*3 timeout loops, but it also means we don't have the i2c bit banging retry at all on -ENXIO, like Todd notes. The questions are, is one retry after -ENXIO in drm_do_probe_ddc_edid enough now? Should we revert the original commit instead since the underlying algorithm has changed? Or should we return something other than -ENXIO from our gmbus code to not hit this exit with no retries path? > This added code to exit immediately if the return code from the > i2c_transfer function was -ENXIO in order to reduce the amount of time spent > in waiting for unresponsive or disconnected devices. For the DP dongles, > this means that the second retry never happens which results in a failed > EDID probe and a black screen. > > To work around this problem without undoing the fix for bug #41059, the > number of retries is checked along with the return code. This allows for a > device to NAK once and still continue operations. A second NAK will result > in breaking the loop as it would have before and stopping the DDC probe. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=85924 Maybe throw this at other dongle bugs you can find too? We're going to need Tested-bys though. BR, Jani. > Signed-off-by: Todd Previte <tprevite@xxxxxxxxx> > Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx > --- > drivers/gpu/drm/drm_edid.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c > index 7087da3..e8047bd 100644 > --- a/drivers/gpu/drm/drm_edid.c > +++ b/drivers/gpu/drm/drm_edid.c > @@ -1238,7 +1238,10 @@ drm_do_probe_ddc_edid(void *data, u8 *buf, unsigned int block, size_t len) > */ > ret = i2c_transfer(adapter, &msgs[3 - xfers], xfers); > > - if (ret == -ENXIO) { > + /* Passive DP->DVI/HDMI dongles sometimes NAK the first probe > + * Try to probe again but if it NAKs, stop trying > + */ > + if (ret == -ENXIO && retries < 5) { > DRM_DEBUG_KMS("drm: skipping non-existent adapter %s\n", > adapter->name); > break; > -- > 1.9.1 > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@xxxxxxxxxxxxxxxxxxxxx > http://lists.freedesktop.org/mailman/listinfo/intel-gfx -- Jani Nikula, Intel Open Source Technology Center _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
