linux-kernel - Re: [PATCH RESEND 2/2] i2c: pnx: Fix read transactions of >= 2 bytes

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Date:	Sat, 18 Aug 2012 11:52:12 +0200
From:	Wolfram Sang <w.sang@...gutronix.de>
To:	Roland Stigge <stigge@...com.de>
Cc:	vitalywool@...il.com, khali@...ux-fr.org, ben-linux@...ff.org,
	grant.likely@...retlab.ca, linux-i2c@...r.kernel.org,
	linux-kernel@...r.kernel.org, kevin.wells@....com,
	srinivas.bakki@....com, aletes.xgr@...il.com, jonsmirl@...il.com
Subject: Re: [PATCH RESEND 2/2] i2c: pnx: Fix read transactions of >= 2 bytes

On Wed, Aug 08, 2012 at 09:42:32AM +0200, Roland Stigge wrote:
> On transactions with n>=2 bytes, the controller actually wrongly clocks in n+1
> bytes. This is caused by the (wrong) assumption that RFE in the Status Register
> is 1 iff there is no byte already ordered (via a dummy TX byte). This lead to
> the implementation of synchronized byte ordering, e.g.:
> 
> Dummy-TX - RX - Dummy-TX - RX - ...
> 
> But since RFE actually stays high after some Dummy-TX, it rather looks like:
> 
> Dummy-TX - Dummy-TX - RX - Dummy-TX - RX - (RX)
> 
> The last RX byte is clocked in by the bus controller, but ignored by the kernel
> when filling the userspace buffer.
> 
> This patch fixes the issue by asking for RX via Dummy-TX asynchronously.
> Introducing a separate counter for TX bytes.
> 
> Signed-off-by: Roland Stigge <stigge@...com.de>
> 
> ---
> Applies to v3.6-rc1
> 
> This patch for i2c-pnx affects PNX4008 and LPC32xx (and LPC31xx, not yet in
> mainline). Can you please test?
> 
> Thanks in advance!

I assume you checked this on LPC32xx? I'll wait a bit more but tend to
take the patch anyhow, even if there is no explicit ACK from PNX.

-- 
Pengutronix e.K.                           | Wolfram Sang                |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |

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