i2c: i2c-mxs: Use DMA mode even for small transfers

commit d6e102f498cbcc8dd2e36721a01213f036397112 upstream.

Recently we have been seing some reports about PIO mode not working properly.

- http://www.spinics.net/lists/linux-i2c/msg11985.html
- http://marc.info/?l=linux-i2c&m=137235593101385&w=2
- https://lkml.org/lkml/2013/6/24/430

Let's use DMA mode even for small transfers.

Without this patch, i2c reads the incorrect sgtl5000 version on a mx28evk when
touchscreen is enabled:

[    5.856270] sgtl5000 0-000a: Device with ID register 0 is not a sgtl5000
[    9.877307] sgtl5000 0-000a: ASoC: failed to probe CODEC -19
[    9.883528] mxs-sgtl5000 sound.12: ASoC: failed to instantiate card -19
[    9.892955] mxs-sgtl5000 sound.12: snd_soc_register_card failed (-19)

[wsa: we have a proper solution for -next, so this non intrusive
solution is OK for now]

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Lucas Stach <l.stach@pengutronix.de>
Acked-by: Marek Vasut <marex@denx.de>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/i2c/busses/i2c-mxs.c b/drivers/i2c/busses/i2c-mxs.c
index 2039f230482db0565c0e4357bc9ae8f38a34757f..6d8094d44987b236cef49e0731d09627497ab2af 100644 (file)
--- a/drivers/i2c/busses/i2c-mxs.c
+++ b/drivers/i2c/busses/i2c-mxs.c
@@ -494,7 +494,7 @@ static int mxs_i2c_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg,
         * based on this empirical measurement and a lot of previous frobbing.
         */
        i2c->cmd_err = 0;
-       if (msg->len < 8) {
+       if (0) {        /* disable PIO mode until a proper fix is made */
                ret = mxs_i2c_pio_setup_xfer(adap, msg, flags);
                if (ret)
                        mxs_i2c_reset(i2c);