RE: [PATCH] arm64: dts: ls1028a: make the eMMC and SD card controllers use fixed indices

[Y.b. Lu]

Hi Michael,

> -----Original Message-----
> From: Michael Walle <michael@xxxxxxxx>
> Sent: Tuesday, November 24, 2020 4:55 PM
> To: Y.b. Lu <yangbo.lu@xxxxxxx>
> Cc: Vladimir Oltean <vladimir.oltean@xxxxxxx>; Shawn Guo
> <shawnguo@xxxxxxxxxx>; Leo Li <leoyang.li@xxxxxxx>; Rob Herring
> <robh+dt@xxxxxxxxxx>; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> devicetree@xxxxxxxxxxxxxxx; Adrian Hunter <adrian.hunter@xxxxxxxxx>; Ulf
> Hansson <ulf.hansson@xxxxxxxxxx>; linux-mmc@xxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx; Ashish Kumar <ashish.kumar@xxxxxxx>
> Subject: Re: [PATCH] arm64: dts: ls1028a: make the eMMC and SD card
> controllers use fixed indices
> 
> Am 2020-11-24 09:47, schrieb Y.b. Lu:
> > Hi Michael,
> >
> >> -----Original Message-----
> >> From: Michael Walle <michael@xxxxxxxx>
> >> Sent: Tuesday, November 24, 2020 4:03 PM
> >> To: Y.b. Lu <yangbo.lu@xxxxxxx>
> >> Cc: Vladimir Oltean <vladimir.oltean@xxxxxxx>; Shawn Guo
> >> <shawnguo@xxxxxxxxxx>; Leo Li <leoyang.li@xxxxxxx>; Rob Herring
> >> <robh+dt@xxxxxxxxxx>; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> >> devicetree@xxxxxxxxxxxxxxx; Adrian Hunter <adrian.hunter@xxxxxxxxx>;
> >> Ulf
> >> Hansson <ulf.hansson@xxxxxxxxxx>; linux-mmc@xxxxxxxxxxxxxxx;
> >> linux-kernel@xxxxxxxxxxxxxxx; Ashish Kumar <ashish.kumar@xxxxxxx>
> >> Subject: Re: [PATCH] arm64: dts: ls1028a: make the eMMC and SD card
> >> controllers use fixed indices
> >>
> >> Am 2020-11-24 08:41, schrieb Y.b. Lu:
> >> > Hi Vladimir,
> >> >
> >> >> -----Original Message-----
> >> >> From: Vladimir Oltean <vladimir.oltean@xxxxxxx>
> >> >> Sent: Friday, November 20, 2020 5:30 PM
> >> >> To: Y.b. Lu <yangbo.lu@xxxxxxx>
> >> >> Cc: Shawn Guo <shawnguo@xxxxxxxxxx>; Leo Li <leoyang.li@xxxxxxx>;
> Rob
> >> >> Herring <robh+dt@xxxxxxxxxx>; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> >> >> devicetree@xxxxxxxxxxxxxxx; Adrian Hunter <adrian.hunter@xxxxxxxxx>;
> >> >> Ulf
> >> >> Hansson <ulf.hansson@xxxxxxxxxx>; linux-mmc@xxxxxxxxxxxxxxx;
> >> >> linux-kernel@xxxxxxxxxxxxxxx; Ashish Kumar <ashish.kumar@xxxxxxx>;
> >> >> Michael Walle <michael@xxxxxxxx>
> >> >> Subject: Re: [PATCH] arm64: dts: ls1028a: make the eMMC and SD card
> >> >> controllers use fixed indices
> >> >>
> >> >> On Fri, Nov 20, 2020 at 02:04:02AM +0000, Y.b. Lu wrote:
> >> >> > Hi Vladimir,
> >> >> >
> >> >> > I have already upstreamed a patch for all affected layerscape boards.
> >> >> >
> >> >>
> >>
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgit.kern
> >>
> el.org%2Fpub%2Fscm%2Flinux%2Fkernel%2Fgit%2Fshawnguo%2Flinux.git%2
> >>
> Fcommit%2F&amp;data=04%7C01%7Cyangbo.lu%40nxp.com%7C498622ade
> >>
> e704fc0042008d8904f6184%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0
> >> %7C0%7C637418017917635725%7CUnknown%7CTWFpbGZsb3d8eyJWIjoi
> M
> >>
> C4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000
> >>
> &amp;sdata=OciS3q%2BmP%2Bz4x1ewPHDigmUkgIZmBgUlRRTm4yaxB7s%3D
> >> &amp;reserved=0?
> >> >> h=imx/dt64&id=342ab37ecaf8c1b10dd3ca9a1271db29a6af0705
> >> >> >
> >> >> > Please check whether it works for you.
> >> >>
> >> >> Thanks, one can tell that I haven't done my due diligence of checking
> >> >> Shawn's tree first. I'll cherry-pick that patch and carry on with my
> >> >> work.
> >> >>
> >> >> However, the fact still remains that Michael has expressed his opinion
> >> >> regarding mmcblk0 vs mmcblk1. Do you think that we could make the
> >> >> aliases a per-board option instead of per-SoC? Consider that there
> >> >> might
> >> >> even be boards that only use SD card. It would be strange for the
> >> >> block
> >> >> device in that case to be called /dev/mmcblk1.
> >> >
> >> > I don't think it's a problem in board dts to define board specific
> >> > thing, like re-defining alias, and disabling any IP it not using.
> >>
> >> First, why would you put it in the architecture include anyway? That
> >> is really board-specific. That is like you would say, we enable all
> >> devices and a board could potentially disable it. TBH it seems that
> >> this will fit your reference boards and you don't care about the
> >> other ones which uses that include.
> >
> > In soc dtsi, this is giving default alias for two esdhc controllers.
> > This is not board specific.
> > That's natural esdhc0 is mmc0 and esdhc1 is mmc1.
> 
> How could this be not board specific if there are at least three
> different use cases the board can choose from - and needs three
> different configurations:
> 
> (1) eMMC at /dev/mmcblk0, SD card at /dev/mmcblk1
> (2) SD card at /dev/mmcblk0, eMMC at /dev/mmcblk1
> (3) no eMMC at all, SD card at /dev/mmcblk0

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.
It's not related to board and card type, it's only related to esdhc interface in use.
Thanks.
> 
> your include only support (1). If a board needs (2) or (3) it has to
> override the configuration in the _common_ include.
> 
> >> And as Vladimir pointed out, what do you do if you just have the eMMC
> >> on the LS1028A. It will be mmcblk1 unless you do something like the
> >> following in the board dts:
> >>
> >> mmc0 = &esdhc;
> >> /delete-property/ mmc1;
> >>
> >> That is really cumbersome, isnt it?
> >
> > The soc dtsi gives default alias to make esdhc0 as mmc0, and esdhc1 as
> > mmc1, the use case just needs to consider which esdhc controller is
> > used. That's fixed index for it.
> > No matter how the board is designed, there are two esdhc controllers
> > in soc. It's probed as mmc0 and mmc1.
> > It's use case that should choose the right mmc device. It is not the
> > dts that should be changed to suit use case.
> > If the board owner insists to change alias to make esdhc1 as mmc0, I
> > think no problem. Just do it in board dts to override the default one.
> 
> Still, why would this be enforced in the common include? What is the
> advnatage here? I only see disadvantages.
> 
> -michael