linux-kernel - Re: [PATCH v8 5/5] spi: dw: Round of n

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Date:   Fri, 21 Apr 2023 22:40:44 +0530
From:   Joy Chakraborty <joychakr@...gle.com>
To:     Serge Semin <fancer.lancer@...il.com>
Cc:     David Laight <David.Laight@...lab.com>,
        Mark Brown <broonie@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...el.com>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "manugautam@...gle.com" <manugautam@...gle.com>,
        "rohitner@...gle.com" <rohitner@...gle.com>
Subject: Re: [PATCH v8 5/5] spi: dw: Round of n_bytes to power of 2

On Fri, Apr 21, 2023 at 10:18 PM Serge Semin <fancer.lancer@...il.com> wrote:
>
> On Fri, Apr 21, 2023 at 04:39:30PM +0000, David Laight wrote:
> > From: Joy Chakraborty
> > > Sent: 21 April 2023 10:22
> > ...
> > > Sure, I can make the following change in the formatting and send the
> > > patch series:
> > >          dws->n_bytes =
> > >                  roundup_pow_of_two(DIV_ROUND_UP(transfer->bits_per_word,
> > >                                                  BITS_PER_BYTE));
> >
>
> > Won't checkpatch bleat about that?
>
> Why would it?

I ran checkpatch on this and it seems to be fine with minor spacing changes.

>
> >
> > Is it ever actually valid for the caller to provide a
> > value that isn't 8, 16 or 32 ?
>
> Judging by this
> https://elixir.bootlin.com/linux/v6.3-rc7/source/drivers/spi/spi.c#L3630
> it is. SPI-controller also supports word lengths within the
> pre-synthesized range. So it's up to the SPI-peripherals and their
> protocols what word length to select.
>
> -Serge(y)
>
> >
> > I'm sure it looked as though some other lengths/counts
> > where likely to go badly wrong.
> >
> > I know there are times when it is useful to bit-bang 'odd'
> > numbers of bits - like command+address+delay for fast reads
> > but that is a sub-32bit transfer so (at least somewhere)
> > is 1 word but not all the bits.
> >
> >       David
> >
> > -
> > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> > Registration No: 1397386 (Wales)