linux-kernel - Re: [PATCH 08/12] arm64: dts: allwinner: h6: Add MMC1 pins

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Message-ID: <20190408224104.qwhk33qgem7bq5y7@core.my.home>
Date:   Tue, 9 Apr 2019 00:41:05 +0200
From:   Ondřej Jirman <megous@...ous.com>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     linux-sunxi@...glegroups.com, Chen-Yu Tsai <wens@...e.org>,
        Rob Herring <robh+dt@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Mark Rutland <mark.rutland@....com>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Jose Abreu <joabreu@...opsys.com>,
        "David S. Miller" <davem@...emloft.net>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Arend van Spriel <arend.vanspriel@...adcom.com>,
        Franky Lin <franky.lin@...adcom.com>,
        Hante Meuleman <hante.meuleman@...adcom.com>,
        Chi-Hsien Lin <chi-hsien.lin@...ress.com>,
        Wright Feng <wright.feng@...ress.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        Naveen Gupta <naveen.gupta@...ress.com>,
        dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com,
        linux-wireless@...r.kernel.org,
        brcm80211-dev-list.pdl@...adcom.com,
        brcm80211-dev-list@...ress.com, linux-gpio@...r.kernel.org
Subject: Re: [PATCH 08/12] arm64: dts: allwinner: h6: Add MMC1 pins

On Mon, Apr 08, 2019 at 09:43:27AM +0200, Maxime Ripard wrote:
> On Sat, Apr 06, 2019 at 01:45:10AM +0200, megous@...ous.com wrote:
> > From: Ondrej Jirman <megous@...ous.com>
> >
> > ---
> >  arch/arm64/boot/dts/allwinner/sun50i-h6.dtsi | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> >
> > diff --git a/arch/arm64/boot/dts/allwinner/sun50i-h6.dtsi b/arch/arm64/boot/dts/allwinner/sun50i-h6.dtsi
> > index 91fecab58836..dccad79da90c 100644
> > --- a/arch/arm64/boot/dts/allwinner/sun50i-h6.dtsi
> > +++ b/arch/arm64/boot/dts/allwinner/sun50i-h6.dtsi
> > @@ -238,6 +238,15 @@
> >  				bias-pull-up;
> >  			};
> >
> > +
> 
> Extra line
> 
> > +			mmc1_pins: mmc1-pins {
> > +				pins = "PG0", "PG1", "PG2", "PG3",
> > +				       "PG4", "PG5";
> > +				function = "mmc1";
> > +				drive-strength = <30>;
> > +				bias-pull-up;
> > +			};
> > +
> 
> Is that the only muxing option?

I don't think so. I believe someone can use a 1-bit interface (bus-width = <1>),
and then some data pins will be free. This pinconfig is for 4-bit bus width
setup.

Though other SoCs (ex. H3, A83T) don't consider this possibility and make the
4-bit config the default pinctrl for mmc1. To add to the confusion, on these
SoCs 4-bit pinconf is the default, but 1bit bus-width is the (implicit) default.
This led to some confusion in the past.

So we can either:
- keep consistency with what is done elsewhere, and make this default, despite
  not being the only option,
- or perhaps I can rename this to mmc1_bus_width4_pins, or somesuch, to make it
  more explicit, and keep it non-default.

What do you think is better?

thank you and regards,
	o.

> If so, then it should be assigned by default to mmc1
> 
> Thanks!
> Maxime
> 
> --
> Maxime Ripard, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com