linux-kernel - Re: [PATCH 4/7 v6] drm/i915/intel

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Date:	Thu, 29 Mar 2012 16:39:16 +0800
From:	Daniel Kurtz <djkurtz@...omium.org>
To:	Chris Wilson <chris@...is-wilson.co.uk>
Cc:	Daniel Vetter <daniel@...ll.ch>, Keith Packard <keithp@...thp.com>,
	David Airlie <airlied@...ux.ie>,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	Benson Leung <bleung@...omium.org>,
	Yufeng Shen <miletus@...omium.org>
Subject: Re: [PATCH 4/7 v6] drm/i915/intel_i2c: use WAIT cycle, not STOP

On Thu, Mar 29, 2012 at 2:48 AM, Chris Wilson <chris@...is-wilson.co.uk> wrote:
> On Thu, 29 Mar 2012 02:26:36 +0800, Daniel Kurtz <djkurtz@...omium.org> wrote:
>> The i915 is only able to generate a STOP cycle (i.e. finalize an i2c
>> transaction) during a DATA or WAIT phase.  In other words, the
>> controller rejects a STOP requested as part of the first transaction in a
>> sequence.
>
> The original docs have "this can only cause a STOP to be generated if a
> GMBUS cycle is generated, the GMBUS is currently in a data phase, or it
> is in a WAIT phase."
>
> So from that it seems STOP | INDEX? | WAIT is always a valid
> combination and is explicitly listed in the register set.
>
> I defer to actual testing though ;)

Unfortunately, STOP on first transaction didn't work for me :(.
Perhaps the docs are missing a "when":

"this can only cause a STOP to be generated if a GMBUS cycle is
generated *when* the GMBUS is currently in a data phase, or it is in a
WAIT phase."



> -Chris
>
> --
> Chris Wilson, Intel Open Source Technology Centre
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