[PATCH v3] i2c: omap: ensure writes to dev->buf_len are ordered

[Wolfram Sang]

On Wed, Nov 14, 2012 at 04:22:45PM +0200, Felipe Balbi wrote:
> if we allow compiler reorder our writes, we could
> fall into a situation where dev->buf_len is reset
> for no apparent reason.
> 
> This bug was found with a simple script which would
> transfer data to an i2c client from 1 to 1024 bytes
> (a simple for loop), when we got to transfer sizes
> bigger than the fifo size, dev->buf_len was reset
> to zero before we had an oportunity to handle XDR
> Interrupt. Because dev->buf_len was zero, we entered
> omap_i2c_transmit_data() to transfer zero bytes,
> which would mean we would just silently exit
> omap_i2c_transmit_data() without actually writing
> anything to DATA register. That would cause XDR
> IRQ to trigger forever and we would never transfer
> the remaining bytes.
> 
> After adding the memory barrier, we also drop resetting
> dev->buf_len to zero in omap_i2c_xfer_msg() because
> both omap_i2c_transmit_data() and omap_i2c_receive_data()
> will act until dev->buf_len reaches zero, rendering the
> other write in omap_i2c_xfer_msg() redundant.
> 
> This patch has been tested with pandaboard for a few
> iterations of the script mentioned above.
> 
> Signed-off-by: Felipe Balbi <balbi at ti.com>

Applied to for-current, thanks!

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