linux-kernel - Re: [PATCH 4/8 v7] drm/i915/intel

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Date:	Wed, 11 Apr 2012 22:04:34 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Daniel Kurtz <djkurtz@...omium.org>
Cc:	Keith Packard <keithp@...thp.com>, David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	Chris Wilson <chris@...is-wilson.co.uk>,
	Benson Leung <bleung@...omium.org>,
	Yufeng Shen <miletus@...omium.org>
Subject: Re: [PATCH 4/8 v7] drm/i915/intel_i2c: use WAIT cycle, not STOP

On Thu, Apr 12, 2012 at 02:16:45AM +0800, Daniel Kurtz wrote:
> On Tue, Apr 10, 2012 at 11:03 PM, Daniel Vetter <daniel@...ll.ch> wrote:
> > - atm the debug output is too noisy. I think we can leave the fallback to
> >  gpio bitbanging at info (or maybe error) level, but all the other
> >  messages should be tuned down to DRM_DEBUG_KMS - these can easily be hit
> >  when userspace tries to probe the i2c with nothing connected or if the
> >  driver code tries to do the same. See:
> >  https://bugs.freedesktop.org/show_bug.cgi?id=48248
> 
> OK...  we can change the logging level.
> However, the log in the bug to which you link seems to indicate a more
> serious issue in this case.  It says to me that something on his
> system is trying to talk to the disabled dpc i2c port 5 times every 10
> seconds.  Each time it fails due with a time out, and each timeout
> takes 50ms.  I would argue that the INFO message here is pointing out
> that the hotplug code might want to check the corresponding
> PORT_ENABLED bit before attempting a read over a particular DP/HDMI
> gmbus port.  Perhaps I am mistaken, but if there was really nothing on
> the bus, shouldn't that be a NAK, not a timeout?

The issue is that there's no hotplug, so we run a polling loop which
checks every 10s whether anything is connected. Part of that is trying to
read an edid. I dunno exactly why we don't get a NAK but a timeout.
-Daniel
-- 
Daniel Vetter
Mail: daniel@...ll.ch
Mobile: +41 (0)79 365 57 48
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