Re: [PATCH RFC 2/2] staging: fbtft: fix 9-bit SPI support detection

[Noralf TrÃnnes]

Den 25.08.2015 19:34, skrev Stefan Wahren:
> > Noralf TrÃnnes <noralf@xxxxxxxxxxx> hat am 25. August 2015 um 00:00
> > geschrieben:
> >
> >
> >
> > Den 24.08.2015 20:33, skrev Stefan Wahren:
> > > Since bits_per_word isn't usually checked during SPI setup the 9-bit
> > > support must be checked manually.
> > >
> > > Signed-off-by: Stefan Wahren <stefan.wahren@xxxxxxxx>
> > > ---
> > > drivers/staging/fbtft/fbtft-core.c | 7 +++++++
> > > drivers/staging/fbtft/flexfb.c | 7 +++++++
> > > 2 files changed, 14 insertions(+)
> > >
> > > diff --git a/drivers/staging/fbtft/fbtft-core.c
> > > b/drivers/staging/fbtft/fbtft-core.c
> > > index 3638554..bd71487 100644
> > > --- a/drivers/staging/fbtft/fbtft-core.c
> > > +++ b/drivers/staging/fbtft/fbtft-core.c
> > > @@ -1438,6 +1438,13 @@ int fbtft_probe_common(struct fbtft_display *display,
> > > if (par->spi && display->buswidth == 9) {
> > > par->spi->bits_per_word = 9;
> > > ret = spi_setup(par->spi);
> > > + if (!ret) {
> > > + struct spi_master *ma = par->spi->master;
> > > +
> > > + if (!(ma->bits_per_word_mask & SPI_BPW_MASK(9)))
> > > + ret = -EINVAL;
> > > + }
> > > +
> > > if (ret) {
> > There's no point in calling spi_setup() when it doesn't check bits_per_word.
> If checking of bits_per_word is the only intention of the setup call, then i
> agree.
> But i'm not sure it is safe to remove the setup call complete.
>
> Couldn't this cause regressions since there is no common spi setup call for all
> drivers?

spi_add_device() calls spi_setup() for all spi devices so it's already done.
If spi_setup() did something with bits_per_word, then I agree that we should
call it in the 9-bit case. But this is not the case, and it's possible to
change bits_per_word per transfer later, so I can't see that this is needed.

> > Apparently this changed with the commit:
> > spi: convert drivers to use bits_per_word_mask.
> > This has not been detected earlier, because FBTFT was previously mostly
> > used on the Raspberry Pi which had a downstream SPI driver that did this
> > check.
> >
> > How about this:
> >
> > - par->spi->bits_per_word = 9;
> > - ret = par->spi->master->setup(par->spi);
> > + if (par->spi->master->bits_per_word_mask &
> > SPI_BPW_MASK(9)) {
> > + par->spi->bits_per_word = 9;
> > - if (ret) {
> > + } else {
> > dev_warn(&par->spi->dev,
> > "9-bit SPI not available, emulating
> > using 8-bit.\n");
> > - par->spi->bits_per_word = 8;
> I think this assignment should stay.

Not needed since we haven't changed the default set by spi_setup():
        if (!spi->bits_per_word)
                spi->bits_per_word = 8;

Callchain for DT registered spi devices:
spi_register_master->of_register_spi_devices->of_register_spi_device->
spi_add_device->spi_setup

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