linux-kernel - Re: [PATCH v2 2/6] ARM: dts: bcm283x: Define standard pinctrl groups in the gpio node.

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Date:   Tue, 13 Sep 2016 08:34:38 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     Stefan Wahren <stefan.wahren@...e.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        linux-rpi-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        Scott Branden <sbranden@...adcom.com>,
        Ray Jui <rjui@...adcom.com>,
        Russell King <linux@...linux.org.uk>,
        open list <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        bcm-kernel-feedback-list@...adcom.com,
        Mark Rutland <mark.rutland@....com>,
        Florian Fainelli <f.fainelli@...il.com>
Subject: Re: [PATCH v2 2/6] ARM: dts: bcm283x: Define standard pinctrl
 groups in the gpio node.

  Hi,

> > > +			emmc_gpio48: emmc_gpio48 {
> > > +				brcm,pins = <48 49 50 51 52 53>;
> > > +				brcm,function = <BCM2835_FSEL_ALT3>;
> > > +			};
> > 
> > Sorry, i didn't notice this before. The naming of these groups suggest 3 muxes
> > for the same eMMC interface. I thought there is a eMMC interface and a SD host
> > interface with different DMA channels.
> > 
> > > +
> > > ...
> > > +
> > > +			sdhost_gpio48: sdhost_gpio48 {
> > > +				brcm,pins = <48 49 50 51 52 53>;
> > > +				brcm,function = <BCM2835_FSEL_ALT0>;
> > > +			};
> > 
> > I think this incorrect. There is no function ALT0 for these pins, only ALT3.
> 
> please forget my last 2 comments. According to this page [1] eMMC is selected by
> ALT3 and sdhost is selected by ALT0.
> 
> Do you know a reliable source where all muxes for both interface are documented?
> The datasheet isn't very helpful here.

No, I don't know any source better than the datasheet @ github.
Yes, I tried to double-check things with the sheet too.

IIRC Eric mentioned a while back in some mail or patch that he checked
something for the rpi device tree with non-public docs, not fully sure
though whenever it was emmc/sdhost or something else.  But I'm basically
trusting Eric here ...

cheers,
  Gerd

PS: This is exactly why I think it us useful to have all those entries
    in the dt file even if unused:  To serve as documentation.