Re: [PATCH 4/6] spi: Add SPIBSC driver

[Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>]

Hi Mark,

On Wed, Dec 4, 2019 at 12:25 PM Mark Brown <broonie@xxxxxxxxxx> wrote:
> On Tue, Dec 03, 2019 at 07:29:45PM +0100, Geert Uytterhoeven wrote:
> > On Tue, Dec 3, 2019 at 3:19 PM Mark Brown <broonie@xxxxxxxxxx> wrote:
> > > > +     pm_runtime_put(&pdev->dev);
> > > > +     pm_runtime_disable(&pdev->dev);
>
> > > There seems to be no purpose in the runtime PM code in this
> > > driver, there's no PM operations of any kind and the driver holds
> > > a runtime PM reference for the entire lifetime of the device.
>
> > It matters for the clock domain (assumed the module clock is not always
> > marked as a critical clock).
>
> That seems like a problem with what the clock domains are doing
> surely?  The default is supposed to be that if runtime PM isn't
> enabled we get the behaviour the driver is manually implementing

Unfortunately not: if the driver doesn't implement Runtime PM, the
default is to not do anything.  Later, unused clocks will be disabled,
and the device will stop functioning.

> here.  Besides, if this is actually impacting power management
> I'd expect us to be letting the IP idle rather than holding it
> powered up all the time.

That would be better, definitely.  However, that's just an optimization over
holding it powered up all the time.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

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