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From:   "Y.b. Lu" <yangbo.lu@nxp.com>
To:     Vladimir Oltean <vladimir.oltean@nxp.com>
CC:     Michael Walle <michael@walle.cc>, Shawn Guo <shawnguo@kernel.org>,
        Leo Li <leoyang.li@nxp.com>, Rob Herring <robh+dt@kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Adrian Hunter <adrian.hunter@intel.com>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        "linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Ashish Kumar <ashish.kumar@nxp.com>
Subject: RE: [PATCH] arm64: dts: ls1028a: make the eMMC and SD card
 controllers use fixed indices
Thread-Topic: [PATCH] arm64: dts: ls1028a: make the eMMC and SD card
 controllers use fixed indices
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Date:   Wed, 25 Nov 2020 02:59:41 +0000
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Hi Vladimir,

> -----Original Message-----
> From: Vladimir Oltean <vladimir.oltean@nxp.com>
> Sent: Tuesday, November 24, 2020 7:28 PM
> To: Y.b. Lu <yangbo.lu@nxp.com>
> Cc: Michael Walle <michael@walle.cc>; Shawn Guo <shawnguo@kernel.org>;
> Leo Li <leoyang.li@nxp.com>; Rob Herring <robh+dt@kernel.org>;
> linux-arm-kernel@lists.infradead.org; devicetree@vger.kernel.org; Adrian
> Hunter <adrian.hunter@intel.com>; Ulf Hansson <ulf.hansson@linaro.org>;
> linux-mmc@vger.kernel.org; linux-kernel@vger.kernel.org; Ashish Kumar
> <ashish.kumar@nxp.com>
> Subject: Re: [PATCH] arm64: dts: ls1028a: make the eMMC and SD card
> controllers use fixed indices
>=20
> On Tue, Nov 24, 2020 at 11:15:19AM +0000, Y.b. Lu wrote:
> > > > Not matter it's SD card or eMMC card, if it's on esdhc0, use
> /dev/mmcblk0.
> > > > Not matter it's SD card or eMMC card, if it's on esdhc1, use
> /dev/mmcblk1.
> > >
> > > With the note here that you can't actually connect an SD card to eSDH=
C1,
> > > due to the lack of pins for CD/WP.
> >
> > CD/WP is not essential to support SD card. Both SD/eMMC are supported o=
n
> both eSDHC controllers.
>=20
> Let's keep that discussion separate. While in theory you might be right,
> I think the real-life complications associated with connecting an eMMC
> to eSDHC0 and an SD card to eSDHC1 will make everyone avoid that. So in
> practice they are still single-purpose.

You may refer to Layerscape QDS boards. 5 types SDHC adapters with PCIe con=
necter supporting SD or eMMC could be used on each esdhc interface.
Another reason using default mmc0 for esdhc0 and mmc1 for esdhc1, is becaus=
e that's also the order before esdhc driver introducing asynchronous probe.
Distros, bootloaders, and users' cases using fixed index before could avoid=
 issues, and been used as they were.
Thanks.

>=20
> > > But it is also natural for a customer to define the indices according=
 to
> > > their schematics and what they use. If, say, there is a board that on=
ly
> > > uses eMMC, I would expect that for the lay person, no one would even =
bat
> > > an eye if that was called /dev/mmcblk0. Whereas, if it was called
> > > /dev/mmcblk1 (and there was no /dev/mmcblk0 in the system), maybe
> you'd
> > > have to come up with some explanations which could be avoided.
> >
> > To make a product friendly to users, it makes sense to define different=
 alias
> for controller in board dts.
> > But it's not the reason to remove the default/natural alias in soc dtsi=
 for two
> controllers.
> > What needs to be done after removing them? Add the same to all other
> board files?
>=20
> Yes.
> In fact, this is also the reason why we prefer to have:
> /soc {
> 	esdhc: mmc@2140000 {
> 		status =3D "disabled";
> 	};
> };
> in fsl-ls1028a.dtsi
> and
> &esdhc {
> 	status =3D "okay";
> };
> in fsl-ls1028a-rdb.dts
> and not the other way around:
>=20
> /soc {
> 	esdhc: mmc@2140000 {
> 		status =3D "okay";
> 	};
> };
> in fsl-ls1028a.dtsi
> and
> &esdhc {
> 	status =3D "disabled";
> };
> in fsl-ls1028a-rdb.dts
>=20
> So, in line with that, I think that the entity that enables the node
> should also define the alias.
>=20
> It's weird to use /delete-property/ if it can be avoided.