Re: [PATCH V2 2/4] mmc: pwrseq: Document DT bindings for the simple MMC power sequence

[NeilBrown <neilb@suse.de>]

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On Thu, 15 Jan 2015 16:58:26 +0000 Mark Rutland <mark.rutland@arm.com> wrote:

> Hi Ulf,
> 
> On Wed, Jan 14, 2015 at 01:02:08PM +0000, Ulf Hansson wrote:
> > The simple MMC power sequence provider, intends to supports a set of
> > common properties between SOC designs. It thus enables us to re-use the
> > same provider for several SOCs.
> > 
> > In this initial step, let's add the top level description of the MMC
> > power sequence and describe the compatible string for the simple MMC
> > power sequence provider.
> > 
> > Following patches will step by step add support for new properties to
> > the simple MMC power sequence provider.
> > 
> > Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
> > ---
> > 
> > Changes in v2:
> > 	- None.
> > 
> > ---
> >  .../devicetree/bindings/mmc/mmc,pwrseq-simple.txt      | 18 ++++++++++++++++++
> >  Documentation/devicetree/bindings/mmc/mmc.txt          |  5 +++++
> >  2 files changed, 23 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/mmc/mmc,pwrseq-simple.txt
> > 
> > diff --git a/Documentation/devicetree/bindings/mmc/mmc,pwrseq-simple.txt b/Documentation/devicetree/bindings/mmc/mmc,pwrseq-simple.txt
> > new file mode 100644
> > index 0000000..e1b7f9c
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/mmc/mmc,pwrseq-simple.txt
> > @@ -0,0 +1,18 @@
> > +* The simple MMC power sequence provider
> > +
> > +System on chip designs may specify a specific MMC power sequence. To
> > +successfully detect an (e)MMC/SD/SDIO card, that power sequence must be
> > +maintained while initializing the card.
> > +
> > +The simple MMC power sequence provider, intends to supports a set of common
> > +properties between SOC designs. It thus enables us to re-use the same provider
> > +for several SOC designs.
> > +
> > +Required properties:
> > +- compatible : contains "mmc,pwrseq-simple".
> 
> Nit: "mmc" is not a vendor prefix.
> 
> > +
> > +Example:
> > +
> > +	sdhci0_pwrseq {
> > +		compatible = "mmc,pwrseq-simple";
> > +	}
> 
> I'm a little confused here. What specific sequence is described by this
> node? We don't appear to have referred to any resources used as part of
> that sequence, and the description above only mentions that there could
> be a specific sequence, not what that sequence is.
> 
> So I don't think this makes sense on its own, and should probably be
> folded with patches adding the initial support for the resources used as
> part of the sequence (e.g. the GPIOs added in a later patch).
> 

I guess I assumed that this "simple" referred to the current behaviour, which
includes some of vmmc-supply, vqmmc-supply, vmmc_aux-supply and pbias-supply
being switched at "appropriate" times.

Would it make sense to bring all of these explicitly under the "pwrseq"
umbrella, leaving the current behaviour only when no pwrseq node is provided?

Also, it isn't clear to me whether the need for power/reset is a function of
the mmc-host, or a function of the device attached to the host.  I suspect
some are needed by one, some by the other.  Any by both?

Should the two needs be kept separate?

NeilBrown


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