linux-kernel - Re: [PATCH 5/7 v6] drm/i915/intel_i2c: use INDEX cycles for i2c read transactions

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Message-ID: <20120329092532.GF4106@phenom.ffwll.local>
Date:	Thu, 29 Mar 2012 11:25:32 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Daniel Kurtz <djkurtz@...omium.org>
Cc:	Chris Wilson <chris@...is-wilson.co.uk>,
	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 5/7 v6] drm/i915/intel_i2c: use INDEX cycles for i2c read
 transactions

On Thu, Mar 29, 2012 at 04:37:18PM +0800, Daniel Kurtz wrote:
> On Thu, Mar 29, 2012 at 2:52 AM, Chris Wilson <chris@...is-wilson.co.uk> wrote:
> > On Thu, 29 Mar 2012 02:26:37 +0800, Daniel Kurtz <djkurtz@...omium.org> wrote:
> >> It is very common for an i2c device to require a small 1 or 2 byte write
> >> followed by a read.  For example, when reading from an i2c EEPROM it is
> >> common to write and address, offset or index followed by a reading some
> >> values.
> >
> > Hmm, I have
> >
> > "gmbus1, bits 8-15: 8-bit GMBUS slave register
> > This field is redundant and should not be used."
> >
> > Scary. :)
> 
> Perhaps INDEX ops are only available on some chipsets?
> Is this something you can double check?

I think index ops are available, the text sounds more like a hint to the
programmer that for VCH devices you should use word reg index access (i.e.
gmbus 5). We'll see when it blows up.
-Daniel
-- 
Daniel Vetter
Mail: daniel@...ll.ch
Mobile: +41 (0)79 365 57 48
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