linux-kernel - Re: [PATCH] spi: dw: support 4-16 bits per word

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Date:   Wed, 8 Aug 2018 13:58:35 +0200
From:   Simon Goldschmidt <simon.k.r.goldschmidt@...il.com>
To:     andy.shevchenko@...il.com
Cc:     Mark Brown <broonie@...nel.org>, linux-spi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] spi: dw: support 4-16 bits per word

On Wed, Aug 8, 2018 at 11:45 AM Andy Shevchenko
<andy.shevchenko@...il.com> wrote:
>
> On Wed, Aug 8, 2018 at 10:14 AM, Simon Goldschmidt
> <simon.k.r.goldschmidt@...il.com> wrote:
> > The spi-dw driver currently only supports 8 or 16 bits per word.
> >
> > Since the hardware supports 4-16 bits per word, adapt the driver
> > to also support this.
> >
> > Tested on socfpga cyclone5 with a 9-bit SPI display.
>
> > +       if ((transfer->bits_per_word < 4) || (transfer->bits_per_word > 16))
> > +               return -EINVAL;
>
> > +       if (transfer->bits_per_word <= 8) {
> >                 dws->n_bytes = 1;
> >                 dws->dma_width = 1;
> > -       } else if (transfer->bits_per_word == 16) {
> > +       } else {
> >                 dws->n_bytes = 2;
> >                 dws->dma_width = 2;
> >         }
>
> Now these can be just
>
> n_bytes = round_up(8);
> dma_width = round_up(8);

I guess you mean:

n_bytes = round_up(transfer->bits_per_word, 8);

But that would yield 8 or 16 where we need 1 or 2.

Reading spi-imx.c, this might work:

n_bytes = DIV_ROUND_UP(transfer->bits_per_word, BITS_PER_BYTE);


Simon