linux-kernel - Re: [PATCH] i2c: ismt: Separate I2C block read from SMBus block read

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Message-ID: <20171005124133.7ue727bib2mlpnyy@ninjato>
Date:   Thu, 5 Oct 2017 14:41:33 +0200
From:   Wolfram Sang <wsa@...-dreams.de>
To:     Pontus Andersson <epontan@...il.com>
Cc:     Seth Heasley <seth.heasley@...el.com>,
        Neil Horman <nhorman@...driver.com>, linux-i2c@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c: ismt: Separate I2C block read from SMBus block read

On Mon, Oct 02, 2017 at 02:45:19PM +0200, Pontus Andersson wrote:
> Commit b6c159a9cb69 ("i2c: ismt: Don't duplicate the receive length for
> block reads") broke I2C block reads. It aimed to fix normal SMBus block
> read, but changed the correct behavior of I2C block read in the process.
> 
> According to Documentation/i2c/smbus-protocol, one vital difference
> between normal SMBus block read and I2C block read is that there is no
> byte count prefixed in the data sent on the wire:
> 
>  SMBus Block Read:  i2c_smbus_read_block_data()
>  S Addr Wr [A] Comm [A]
>             S Addr Rd [A] [Count] A [Data] A [Data] A ... A [Data] NA P
> 
>  I2C Block Read:  i2c_smbus_read_i2c_block_data()
>  S Addr Wr [A] Comm [A]
>             S Addr Rd [A] [Data] A [Data] A ... A [Data] NA P
> 
> Therefore the two transaction types need to be processed differently in
> the driver by copying of the dma_buffer as done previously for the
> I2C_SMBUS_I2C_BLOCK_DATA case.
> 
> Fixes: b6c159a9cb69 ("i2c: ismt: Don't duplicate the receive length for block reads")
> Signed-off-by: Pontus Andersson <epontan@...il.com>
> Cc: stable@...r.kernel.org

Applied to for-current, thanks!

Might have been good to CC the patch author of the problematic commit,
too.


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