Re: [PATCH 4/4] spi: bcm2835aux: fix CPOL/CPHA setting

[Stephan Olbrich <stephanolbrich-Mmb7MZpHnFY@public.gmane.org>]

Am Tuesday 09 February 2016, 16:13:06 schrieb Eric Anholt:
> stephanolbrich-Mmb7MZpHnFY@public.gmane.org writes:
> > From: Stephan Olbrich <stephanolbrich-Mmb7MZpHnFY@public.gmane.org>
> > 
> > The auxiliary spi supports only CPHA=0 modes as the first bit is
> > always output to the pin before the first clock cycle. In CPHA=1
> > modes the first clock edge outputs the second bit hence the slave
> > can never read the first bit.
> > 
> > Also the CPHA registers switch between clocking data in/out on
> > rising/falling edge hence depend on the CPOL setting.
> > 
> > Signed-off-by: Stephan Olbrich <stephanolbrich-Mmb7MZpHnFY@public.gmane.org>
> > ---
> > 
> >  drivers/spi/spi-bcm2835aux.c | 10 +++++-----
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/spi/spi-bcm2835aux.c b/drivers/spi/spi-bcm2835aux.c
> > index b90aa34..169f521 100644
> > --- a/drivers/spi/spi-bcm2835aux.c
> > +++ b/drivers/spi/spi-bcm2835aux.c
> > @@ -386,12 +386,12 @@ static int bcm2835aux_spi_prepare_message(struct
> > spi_master *master,> 
> >  	bs->cntl[1] = BCM2835_AUX_SPI_CNTL1_MSBF_IN;
> >  	
> >  	/* handle all the modes */
> > 
> > -	if (spi->mode & SPI_CPOL)
> > +	if (spi->mode & SPI_CPOL) {
> > 
> >  		bs->cntl[0] |= BCM2835_AUX_SPI_CNTL0_CPOL;
> > 
> > -	if (spi->mode & SPI_CPHA)
> > -		bs->cntl[0] |= BCM2835_AUX_SPI_CNTL0_CPHA_OUT |
> > -			       BCM2835_AUX_SPI_CNTL0_CPHA_IN;
> > -
> > +		bs->cntl[0] |= BCM2835_AUX_SPI_CNTL0_CPHA_OUT;
> > +	} else {
> > +		bs->cntl[0] |= BCM2835_AUX_SPI_CNTL0_CPHA_IN;
> > +	}
> > 
> >  	bcm2835aux_wr(bs, BCM2835_AUX_SPI_CNTL1, bs->cntl[1]);
> >  	bcm2835aux_wr(bs, BCM2835_AUX_SPI_CNTL0, bs->cntl[0]);
> 
> (Note for other readers: A better name for CNTL0_CPHA_* would be
> CNTL0_*_RISING).

Should I rename them? 

> I think you're right about not actually supporting CPHA.  I don't see
> wany way to keep bit 1 out lasting through the first full clock cycle.
> I think Stefan's right that we should drop CPHA from MODE_BITS
> (actually, MODE_BITS would be nicer if we just merged it into its one
> user, I think).

You are right. I'll fix that.

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