linux-kernel - Re: [PATCH v2 5/5] ARM: dts: ls1021a-tsn: Use the DSPI controller in poll mode

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Date:   Wed, 11 Sep 2019 09:00:03 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Shawn Guo <shawnguo@...nel.org>
Cc:     Vladimir Oltean <olteanv@...il.com>,
        Mark Brown <broonie@...nel.org>,
        linux-spi <linux-spi@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, netdev <netdev@...r.kernel.org>,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v2 5/5] ARM: dts: ls1021a-tsn: Use the DSPI controller in
 poll mode

On Wed, Sep 11, 2019 at 8:34 AM Shawn Guo <shawnguo@...nel.org> wrote:
> On Tue, Aug 27, 2019 at 09:16:39PM +0300, Vladimir Oltean wrote:
> > On Tue, 27 Aug 2019 at 21:13, Mark Brown <broonie@...nel.org> wrote:
> > > On Tue, Aug 27, 2019 at 09:06:14PM +0300, Vladimir Oltean wrote:
> > > > On Tue, 27 Aug 2019 at 21:05, Mark Brown <broonie@...nel.org> wrote:
> > > > > On Mon, Aug 26, 2019 at 04:10:51PM +0300, Vladimir Oltean wrote:
> > >
> > > > > > I noticed you skipped applying this patch, and I'm not sure that Shawn
> > > > > > will review it/take it.
> > > > > > Do you have a better suggestion how I can achieve putting the DSPI
> > > > > > driver in poll mode for this board? A Kconfig option maybe?
> > >
> > > > > DT changes go through the relevant platform trees, not the
> > > > > subsystem trees, so it's not something I'd expect to apply.
> > >
> > > > But at least is it something that you expect to see done through a
> > > > device tree change?
> > >
> > > Well, it's not ideal - if it performs better all the time the
> > > driver should probably just do it unconditionally.  If there's
> > > some threashold where it tends to perform better then the driver
> > > should check for that but IIRC it sounds like the interrupt just
> > > isn't at all helpful here.
> >
> > I can't seem to find any situation where it performs worse. Hence my
> > question on whether it's a better idea to condition this behavior on a
> > Kconfig option rather than a DT blob which may or may not be in sync.
>
> DT is a description of hardware not condition for software behavior,
> where module parameter is usually used for.

+1

DT says the interrupt line is wired.
The driver should know if it should make use of the interrupt, or not.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds