linux-kernel - Re: [RFC PATCH v2 3/3] mmc: renesas_sdhi: Add support for RZ/V2H(P) SoC

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Date: Thu, 20 Jun 2024 10:43:41 +0100
From: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To: Biju Das <biju.das.jz@...renesas.com>
Cc: Wolfram Sang <wsa+renesas@...g-engineering.com>, 
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>, 
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>, Conor Dooley <conor+dt@...nel.org>, 
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>, Ulf Hansson <ulf.hansson@...aro.org>, 
	Magnus Damm <magnus.damm@...il.com>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Geert Uytterhoeven <geert+renesas@...der.be>, 
	Prabhakar Mahadev Lad <prabhakar.mahadev-lad.rj@...renesas.com>, 
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v2 3/3] mmc: renesas_sdhi: Add support for RZ/V2H(P) SoC

Hi Biju,

On Thu, Jun 20, 2024 at 10:30 AM Biju Das <biju.das.jz@...renesas.com> wrote:
>
> Hi Wolfram, Prabhakar,
>
> > -----Original Message-----
> > From: Wolfram Sang <wsa+renesas@...g-engineering.com>
> > Sent: Thursday, June 20, 2024 8:40 AM
> > Subject: Re: [RFC PATCH v2 3/3] mmc: renesas_sdhi: Add support for RZ/V2H(P) SoC
> >
> > Hi Prabhakar,
> >
> > > I did give it a try with platform_driver_probe() and failed.
> >
> > Ok, thanks for trying nonetheless!
> >
> > > - Firstly I had to move the regulator node outside the SDHI node for
> > > platform_driver_probe() to succeed or else it failed with -ENODEV (at
> > > https://elixir.bootlin.com/linux/latest/source/drivers/base/platform.c
> > > #L953)
> >
> > This makes sense to me because it is just a "regular" regulator.
> >
> > > - In Renesas SoCs we have multiple instances of SDHI, the problem
> > > being for each instance we are calling platform_driver_probe(). Which
> > > causes a problem as the regulator node will use the first device.
> >
> > I see... we would need a reg property to differentiate between the internal regulators but that is
> > already used by the parent SDHI node.
> >
> > Okay, so let's scrap that idea. However, we need to ensure that we can still have an external
> > regulator. Seeing the bindings, it looks like you enable the internal regulator with the "vqmmc-
> > r9a09g057-regulator"
> > property? I wonder now if we can simplify this to an "use-internal-regulator" property because we
> > have 'compatible' already to differentiate? Needs advice from DT maintainers, probably.
>
> Why this cannot be modelled as a regular "regulator" as a child device of SDHI device?
>
The current implementation does implement the regulator as a child
device of the sdhi node [0] itself.

Wolfram was suggesting to have the regulator outside and use
platform_driver_probe(), which caused an issue as mentioned above.

[0] https://patchwork.kernel.org/project/linux-renesas-soc/patch/20240613091721.525266-2-prabhakar.mahadev-lad.rj@bp.renesas.com/

Cheers,
Prabhakar