linux-kernel - Re: [RFC 04/25] spi: gpio: Implement LSB First bitbang support

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Date:   Thu, 12 Dec 2019 17:19:22 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Andreas Färber <afaerber@...e.de>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-realtek-soc@...ts.infradead.org, linux-leds@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        Jacek Anaszewski <jacek.anaszewski@...il.com>,
        Pavel Machek <pavel@....cz>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Dan Murphy <dmurphy@...com>
Subject: Re: [RFC 04/25] spi: gpio: Implement LSB First bitbang support

On Thu, Dec 12, 2019 at 04:14:59PM +0100, Andreas Färber wrote:
> Am 12.12.19 um 09:40 schrieb Geert Uytterhoeven:
> > On Thu, Dec 12, 2019 at 4:41 AM Andreas Färber <afaerber@...e.de> wrote:
> >> Add support for slave DT property spi-lsb-first, i.e., SPI_LSB_FIRST mode.

> >> Duplicate the inline helpers bitbang_txrx_be_cpha{0,1} as LE versions.
> >> Make checkpatch.pl happy by changing "unsigned" to "unsigned int".

Separate patch for this?

> So from that angle I don't see a better way than either duplicating the
> functions or using some macro magic to #include the header twice. If we
> wanted to go down that path, we could probably de-duplicate the existing
> two functions, too, but I was trying to err on the cautious side, since
> I don't have setups to test all four code paths myself (and a ton of
> more relevant but less fun patches to flush out ;)).

Yeah, I don't think there's any great options here with the potential
performance issues - probably the nicest thing would be to autogenerate
lots of variants but I think that's far more trouble than it's worth.

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