On Thu, May 28, 2015 at 02:36:01PM +0300, Jani Nikula wrote: > On Thu, 28 May 2015, Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote: > > On Thu, May 28, 2015 at 01:05:39PM +0300, Jani Nikula wrote: > >> Passive DP->DVI/HDMI dongles on DP++ ports 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 [1]: > >> > >> 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 > >> > >> 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. That was > >> possible because the underlying i2c bit banging algorithm had retries of > >> its own (which, of course, were part of the reason for the bug the > >> commit fixes). > >> > >> Since its introduction in > >> > >> commit f899fc64cda8569d0529452aafc0da31c042df2e > >> Author: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> > >> Date: Tue Jul 20 15:44:45 2010 -0700 > >> > >> drm/i915: use GMBUS to manage i2c links > >> > >> we've been flipping back and forth enabling the GMBUS transfers, but > >> we've settled since then. The GMBUS implementation does not do any > >> retries, however, bailing out of the drm_do_probe_ddc_edid() retry loop > >> on first encounter of -ENXIO. This, combined with Eugeni's commit, broke > >> the retry on -ENXIO. > >> > >> Retry GMBUS once on -ENXIO to mitigate the issues with passive adapters. > >> > >> This patch is based on the work, and commit message, by Todd Previte > >> <tprevite@xxxxxxxxx>. > >> > >> [1] https://bugs.freedesktop.org/show_bug.cgi?id=41059 > >> > >> v2: Don't retry if using bit banging. > >> > >> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=85924 > >> Cc: Todd Previte <tprevite@xxxxxxxxx> > >> Cc: stable@xxxxxxxxxxxxxxx > >> Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx> > >> --- > >> drivers/gpu/drm/i915/intel_i2c.c | 25 ++++++++++++++++++++++--- > >> 1 file changed, 22 insertions(+), 3 deletions(-) > >> > >> diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c > >> index 92072f56e418..c3f72b509d1f 100644 > >> --- a/drivers/gpu/drm/i915/intel_i2c.c > >> +++ b/drivers/gpu/drm/i915/intel_i2c.c > >> @@ -478,9 +478,7 @@ gmbus_xfer_index_read(struct drm_i915_private *dev_priv, struct i2c_msg *msgs) > >> } > >> > >> static int > >> -gmbus_xfer(struct i2c_adapter *adapter, > >> - struct i2c_msg *msgs, > >> - int num) > >> +do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num) > >> { > >> struct intel_gmbus *bus = container_of(adapter, > >> struct intel_gmbus, > >> @@ -593,6 +591,27 @@ out: > >> return ret; > >> } > >> > >> +static int > >> +gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num) > >> +{ > >> + struct intel_gmbus *bus = container_of(adapter, struct intel_gmbus, > >> + adapter); > >> + int ret; > >> + > >> + ret = do_gmbus_xfer(adapter, msgs, num); > >> + > >> + /* > >> + * Passive adapters sometimes NAK the first probe. Retry once on -ENXIO > >> + * for GMBUS transfers; the bit banging algorithm has retries > >> + * internally. See also the retry loop in drm_do_probe_ddc_edid, which > >> + * bails out on the first -ENXIO. > >> + */ > >> + if (ret == -ENXIO && !bus->force_bit) > >> + ret = do_gmbus_xfer(adapter, msgs, num); > > > > i2c-algo-bit does the retry for each msg when sending the address. This > > on the other hand will redo the entire transfer. So if we get a nak but > > not on the first message we end up repeating the succesful part of the > > transfer twice. > > Which is also the case for the retry loop in drm_do_probe_ddc_edid for > errors other than -ENXIO. > > How likely do you think it is to *not* get -ENXIO at first, but get it > in a later message? > > > To match i2c-algo-bit we'd need to do the retry for each individual > > message. I suppose that would make the error handling more > > complicated as we'd supposedly still need to clear the error, but > > then repeat the same msg without generating a STOP in between. > > Looking at the code, and i2c-algo-bit.c, I'm not sure if I'd be > comfortable backporting something like that to stable. It does get > complicated. So sure, this is an attempt to pick the low hanging fruit. > > Do you think this makes the driver worse? > > I plead item (c) of the Reviewer's statement of oversight. ;) Doesn't look too complicated tdrt here: diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c index 92072f56e418..ae9f4be1b644 100644 --- a/drivers/gpu/drm/i915/intel_i2c.c +++ b/drivers/gpu/drm/i915/intel_i2c.c @@ -486,7 +486,7 @@ gmbus_xfer(struct i2c_adapter *adapter, struct intel_gmbus, adapter); struct drm_i915_private *dev_priv = bus->dev_priv; - int i, reg_offset; + int i = 0, reg_offset; int ret = 0; intel_aux_display_runtime_get(dev_priv); @@ -499,9 +499,10 @@ gmbus_xfer(struct i2c_adapter *adapter, reg_offset = dev_priv->gpio_mmio_base; +retry: I915_WRITE(GMBUS0 + reg_offset, bus->reg0); - for (i = 0; i < num; i++) { + for (i; i < num; i++) { if (gmbus_is_index_read(msgs, i, num)) { ret = gmbus_xfer_index_read(dev_priv, &msgs[i]); i += 1; /* set i to the index of the read xfer */ @@ -576,6 +577,9 @@ clear_err: adapter->name, msgs[i].addr, (msgs[i].flags & I2C_M_RD) ? 'r' : 'w', msgs[i].len); + if (bla) + goto retry; + goto out; timeout: --- Totally untested ofc ;-) Cheers, Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
