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

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Message-ID: <20230421171552.qvunrlxxpqusd5h3@mobilestation>
Date:   Fri, 21 Apr 2023 20:15:52 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Joy Chakraborty <joychakr@...gle.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 10:40:44PM +0530, Joy Chakraborty wrote:
> 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.

What spacing do you mean? No problem with the change as is:
[fancer@...ilestation] kernel $ git show HEAD | grep -A1 -B2 roundup_pow_of_two
-	dws->n_bytes = DIV_ROUND_UP(transfer->bits_per_word, BITS_PER_BYTE);
+	dws->n_bytes =
+		roundup_pow_of_two(DIV_ROUND_UP(transfer->bits_per_word,
+						BITS_PER_BYTE));
[fancer@...ilestation] kernel $ ./scripts/checkpatch.pl --git HEAD
total: 0 errors, 0 warnings, 10 lines checked

Commit e18b699257db ("spi: dw: Round of n_bytes to power of 2") has no obvious style problems and is ready for submission.

-Serge(y)

> 
> >
> > >
> > > 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)