Re: [PATCH v2] i2c: i2c-mxs: Use DMA mode even for small transfers

[Marek Vasut <marex@denx.de>]

Dear Lucas Stach,

> Am Montag, den 01.07.2013, 18:14 -0300 schrieb Fabio Estevam:
> > From: Fabio Estevam <fabio.estevam@freescale.com>
> > 
> > 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)
> > 
> > Cc: <stable@vger.kernel.org>
> > Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
> > ---
> > Applies against 3.10
> > 
> > Changes since v1:
> > - Keep the PIO code
> > 
> >  drivers/i2c/busses/i2c-mxs.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/i2c/busses/i2c-mxs.c b/drivers/i2c/busses/i2c-mxs.c
> > index 2039f23..6d8094d 100644
> > --- 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);
> 
> I still plan to take another look at the PIO mode, but higher priority
> things keep popping up in front of me. So this patch is:
> Acked-by: Lucas Stach <l.stach@pengutronix.de>

Ok, update. So far I arrived at a point where I can avoid the PIO trouble.

If I only do transfers shorter or equal in length to 3 bytes via PIO, it works 
as expected. If the transfer is longer, the LA shows very long transfer 
happening actually. Therefore, the pumping of data in loop to/from PIO via the 
DATA register doesn't work.

I will update you more later, once I figure out something else. Now I need some 
sleep.

Best regards,
Marek Vasut