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

From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Mark Brown <broonie@kernel.org>
Cc: Chris Brandt <chris.brandt@renesas.com>,
	Rob Herring <robh+dt@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Geert Uytterhoeven <geert+renesas@glider.be>,
	Michael Turquette <mturquette@baylibre.com>,
	Stephen Boyd <sboyd@kernel.org>,
	linux-spi <linux-spi@vger.kernel.org>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
	<devicetree@vger.kernel.org>,
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
	linux-clk <linux-clk@vger.kernel.org>,
	Mason Yang <masonccyang@mxic.com.tw>,
	Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Subject: Re: [PATCH 4/6] spi: Add SPIBSC driver
Date: Wed, 4 Dec 2019 13:14:09 +0100	[thread overview]
Message-ID: <CAMuHMdXY4Po4p0uL_6VU7ia4R7i7F5N+GA4MUaQfhGFvpgLT7g@mail.gmail.com> (raw)
In-Reply-To: <20191204112528.GQ1998@sirena.org.uk>

Hi Mark,

On Wed, Dec 4, 2019 at 12:25 PM Mark Brown <broonie@kernel.org> 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@kernel.org> 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@linux-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