linux-kernel - Re: [PATCH v8 1/3] dt-bindings: mmc: mtk-sd: extend interrupts and pinctrls properties

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Date:   Tue, 22 Mar 2022 17:33:55 +0800
From:   Axe Yang <axe.yang@...iatek.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        "Rob Herring" <robh@...nel.org>
CC:     Ulf Hansson <ulf.hansson@...aro.org>,
        Chaotian Jing <chaotian.jing@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Satya Tangirala <satyat@...gle.com>,
        "Andy Shevchenko" <andriy.shevchenko@...ux.intel.com>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Lucas Stach <dev@...xeye.de>,
        "Eric Biggers" <ebiggers@...gle.com>,
        Andrew Jeffery <andrew@...id.au>,
        "Stephen Boyd" <swboyd@...omium.org>,
        Kiwoong Kim <kwmad.kim@...sung.com>,
        Yue Hu <huyue2@...ong.com>, Tian Tao <tiantao6@...ilicon.com>,
        <linux-mmc@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v8 1/3] dt-bindings: mmc: mtk-sd: extend interrupts and
 pinctrls properties

Hello AngeloGioacchino,

On Tue, 2022-03-22 at 09:42 +0100, AngeloGioacchino Del Regno wrote:
> Il 22/03/22 02:35, Axe Yang ha scritto:
> > On Mon, 2022-03-21 at 18:29 -0500, Rob Herring wrote:
> > > On Mon, Mar 21, 2022 at 07:51:32PM +0800, Axe Yang wrote:
> > > > Extend interrupts and pinctrls for SDIO wakeup interrupt
> > > > feature.
> > > > This feature allow SDIO devices alarm asynchronous interrupt to
> > > > host
> > > > even when host stop providing clock to SDIO card. An extra
> > > > wakeup
> > > > interrupt and pinctrl states for SDIO DAT1 pin state switching
> > > > are
> > > > required in this scenario.
> > > > 
> > > > Signed-off-by: Axe Yang <axe.yang@...iatek.com>
> > > > ---
> > > >   .../devicetree/bindings/mmc/mtk-sd.yaml       | 23
> > > > ++++++++++++++++++-
> > > >   1 file changed, 22 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/mmc/mtk-sd.yaml
> > > > b/Documentation/devicetree/bindings/mmc/mtk-sd.yaml
> > > > index 297ada03e3de..f57774535a1d 100644
> > > > --- a/Documentation/devicetree/bindings/mmc/mtk-sd.yaml
> > > > +++ b/Documentation/devicetree/bindings/mmc/mtk-sd.yaml
> > > > @@ -69,12 +69,23 @@ properties:
> > > >         - const: ahb_cg
> > > >   
> > > >     interrupts:
> > > > -    maxItems: 1
> > > > +    description:
> > > > +      Should at least contain MSDC GIC interrupt. To support
> > > > SDIO
> > > > in-band wakeup, an extended
> > > > +      interrupt is required and be configured as wakeup source
> > > > irq.
> > > > +    minItems: 1
> > > > +    maxItems: 2
> > > >   
> > > >     pinctrl-names:
> > > > +    description:
> > > > +      Should at least contain default and state_uhs. To
> > > > support
> > > > SDIO in-band wakeup, dat1 pin
> > > > +      will be switched between GPIO mode and SDIO DAT1 mode,
> > > > state_eint and state_dat1 are
> > > > +      mandatory in this scenarios.
> > > > +    minItems: 2
> > > >       items:
> > > >         - const: default
> > > >         - const: state_uhs
> > > > +      - const: state_eint
> > > > +      - const: state_dat1
> > > >   
> > > >     pinctrl-0:
> > > >       description:
> > > > @@ -86,6 +97,16 @@ properties:
> > > >         should contain uhs mode pin ctrl.
> > > >       maxItems: 1
> > > >   
> > > > +  pinctrl-2:
> > > > +    description:
> > > > +      should switch dat1 pin to GPIO mode.
> > > > +    maxItems: 1
> > > > +
> > > > +  pinctrl-3:
> > > > +    description:
> > > > +      should switch SDIO dat1 pin from GPIO mode back to SDIO
> > > > mode.
> > > 
> > > How is this different than pinctrl-0?
> > 
> > pinctrl-0 contains default settings for all IO pins(CLK/CMD/DAT).
> > pinctrl-1 contains settings for all IO pins(CLK/CMD/DAT) in UHS
> > mode.
> > pinctrl-3 is lightweight pinctrl-1, only keep SDIO DAT1 pin
> > function
> > switch part.
> > 
> 
> Is there any particular reason why we cannot simply select pinctrl-1
> again
> instead of pinctrl-3, apart from the virtually not existent overhead
> of one more mmio write?

No, there is no particular reason. 
I just want to do the pin function switch quick and clean. 

The intention of pinctrl-1 is to set the most initial state of IO pins
in UHS mode. If I don't need to adjust IO settings any longer, it is
okay to select pinctrl-1 state instead of pinctrl-3. 
But think about this scenarios: after initial SDIO IO pins to UHS mode,
I want to adjust some IO related properties, such as driving strength.
And I want to keep these settings because with new driving strength,
the signal is better. I'd rather to choose pinctrl-3 but not pinctrl-1, 
because I do not want the change be restored after next runtime resume.

Regards,
Axe