linux-kernel - Re: [PATCH 6/9] drm/i915/intel_i2c: return -ENXIO for device NAK

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Date:	Wed, 07 Mar 2012 12:53:21 +0000
From:	Chris Wilson <chris@...is-wilson.co.uk>
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,
	Benson Leung <bleung@...omium.org>,
	Yufeng Shen <miletus@...omium.org>,
	Sameer Nanda <snanda@...omium.org>
Subject: Re: [PATCH 6/9] drm/i915/intel_i2c: return -ENXIO for device NAK

On Wed, 7 Mar 2012 20:41:03 +0800, Daniel Kurtz <djkurtz@...omium.org> wrote:
> On Wed, Mar 7, 2012 at 8:12 PM, Chris Wilson <chris@...is-wilson.co.uk> wrote:
> > On Wed,  7 Mar 2012 19:50:47 +0800, Daniel Kurtz <djkurtz@...omium.org> wrote:
> >> Return -ENXIO if a device NAKs a transaction.
> >>
> >> Note: We should return -ETIMEDOUT, too if the transaction times out,
> >> however, that error path is currently handled by the 'bit-bang fallback'.
> >>
> >> Signed-off-by: Daniel Kurtz <djkurtz@...omium.org>
> >
> > Can you clarify what the rule is if an error is detected part-way
> > through a xfer?
> 
> A priceless comment from drivers/i2c/i2c-core::i2c_transfer...

Thanks, that is about as consistent as one expects with i2c. ;)
 
> This doesn't specify what to do if the transfer doesn't get an ACK
> during another phase of the transfer.
> However, it does say to send -ENXIO "if no ACK during address phase",
> which is a subset of the possible no-ACK conditions during a transfer.
>  Thus, I choose to return ENXIO in all no-ACK cases, to ensure we send
> it during the one case that is specified.

This (and a summary of the rest) deserves to be captured as a comment in
the code.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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