Re: [PATCH 2/4] iio: ad7949: fix incorrect SPI xfer len

[Andrea Merello <andrea.merello@gmail.com>]

Il giorno ven 13 set 2019 alle ore 08:46 Ardelean, Alexandru
<alexandru.Ardelean@analog.com> ha scritto:
>
> On Thu, 2019-09-12 at 16:43 +0200, Andrea Merello wrote:
> > [External]
> >
> > This driver supports 14-bits and 16-bits devices. All of them have a 14-bit
> > configuration registers. All SPI trasfers, for reading AD conversion
> > results and for writing the configuration register, fit in two bytes.
> >
> > The driver always uses 4-bytes xfers which seems at least pointless (maybe
> > even harmful). This patch trims the SPI xfer len and the buffer size to
> > two bytes.
> >
>
> The length reduction proposal is fine.
>
> But, this patch raises a question about endianess.
> I'm actually wondering here if we need to see about maybe using a __be16 vs u16.
>
> I'm not that kernel-savy yet about some of these low-level things to be completely sure here.
> So, I'd let someone else maybe handle it.

Good point.. It seems that indeed not much care has been taken about
endianess here.. Probably we need also some le16_to_cpu() and
firends..

Maybe another separate patch can be made to take care about endianess later on?

BTW Also, the  ____cacheline_aligned is a bit scaring :) I don't know
what is that for...

>
> Thanks
> Alex
>
> > Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
> > ---
> >  drivers/iio/adc/ad7949.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/iio/adc/ad7949.c b/drivers/iio/adc/ad7949.c
> > index 518044c31a73..5c2b3446fa4a 100644
> > --- a/drivers/iio/adc/ad7949.c
> > +++ b/drivers/iio/adc/ad7949.c
> > @@ -54,7 +54,7 @@ struct ad7949_adc_chip {
> >       u8 resolution;
> >       u16 cfg;
> >       unsigned int current_channel;
> > -     u32 buffer ____cacheline_aligned;
> > +     u16 buffer ____cacheline_aligned;
> >  };
> >
> >  static int ad7949_spi_write_cfg(struct ad7949_adc_chip *ad7949_adc, u16 val,
> > @@ -67,7 +67,7 @@ static int ad7949_spi_write_cfg(struct ad7949_adc_chip *ad7949_adc, u16 val,
> >       struct spi_transfer tx[] = {
> >               {
> >                       .tx_buf = &ad7949_adc->buffer,
> > -                     .len = 4,
> > +                     .len = 2,
> >                       .bits_per_word = bits_per_word,
> >               },
> >       };
> > @@ -95,7 +95,7 @@ static int ad7949_spi_read_channel(struct ad7949_adc_chip *ad7949_adc, int *val,
> >       struct spi_transfer tx[] = {
> >               {
> >                       .rx_buf = &ad7949_adc->buffer,
> > -                     .len = 4,
> > +                     .len = 2,
> >                       .bits_per_word = bits_per_word,
> >               },
> >       };