linux-kernel - Re: [PATCH 3/4] dt-bindings: reset: uniphier: Add AHCI core reset description

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Message-Id: <20181112210215.2DB6.4A936039@socionext.com>
Date:   Mon, 12 Nov 2018 21:02:16 +0900
From:   Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
To:     Philipp Zabel <p.zabel@...gutronix.de>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        DTML <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Masami Hiramatsu <masami.hiramatsu@...aro.org>,
        Jassi Brar <jaswinder.singh@...aro.org>
Subject: Re: [PATCH 3/4] dt-bindings: reset: uniphier: Add AHCI core reset description

Hi,

Thank you for some comments and pointing out.

On Sat, 10 Nov 2018 01:14:06 +0900 <yamada.masahiro@...ionext.com> wrote:

> On Sat, Nov 10, 2018 at 12:02 AM Philipp Zabel <p.zabel@...gutronix.de> wrote:
> >
> > Hi Kunihiko,
> >
> > On Fri, 2018-11-09 at 10:42 +0900, Kunihiko Hayashi wrote:
> > > Add compatible strings for reset control of AHCI core implemented in
> > > UniPhier SoCs. The reset control belongs to AHCI glue layer.
> > >
> > > Signed-off-by: Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
> > > ---
> > >  Documentation/devicetree/bindings/reset/uniphier-reset.txt | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> > > diff --git a/Documentation/devicetree/bindings/reset/uniphier-reset.txt b/Documentation/devicetree/bindings/reset/uniphier-reset.txt
> > > index f63c511..ea00517 100644
> > > --- a/Documentation/devicetree/bindings/reset/uniphier-reset.txt
> > > +++ b/Documentation/devicetree/bindings/reset/uniphier-reset.txt
> > > @@ -133,6 +133,9 @@ Required properties:
> > >      "socionext,uniphier-pxs2-usb3-reset" - for PXs2 SoC USB3
> > >      "socionext,uniphier-ld20-usb3-reset" - for LD20 SoC USB3
> > >      "socionext,uniphier-pxs3-usb3-reset" - for PXs3 SoC USB3
> > > +    "socionext,uniphier-pro4-ahci-reset" - for Pro4 SoC AHCI
> > > +    "socionext,uniphier-pxs2-ahci-reset" - for PXs2 SoC AHCI
> > > +    "socionext,uniphier-pxs3-ahci-reset" - for PXs3 SoC AHCI
> >
> > Since the driver behaves identically for "socionext,uniphier-pro4-usb3-
> > reset" and "socionext,uniphier-pro4-ahci-reset", would it make sense to
> > add a common compatible?
> 
> 
> As far as I could guess, he just happened to find the same driver code
> could be reused for other hardware.
> 
> Theoretically, this can happen anywhere since
> a reset controller is just a set of registers
> each bit of which is connected to a reset line.
> 
> If you added a super-generic compatible like "simple-reset",
> I would agree with
> "socionext,uniphier-pro4-usb3-reset", "simple-reset"
> since this is a pattern.

I think it's more generic to define simple-reset with parent clock/reset
control without both SoC and device names.

However, such parent clocks/resets strongly depends on SoC, 
so I think it's difficut to lead generic definition in this case.

If we add generic compatible string, I also add "simple-reset".


> However,
> "socionext,uniphier-pro4-glue-reset" is kind of a halfway house
> where it is SoC-specific, but still ambiguous.

Surely, it might be hard to understand that pro4-glue-reset is SoC-specific
but for generic-device.


> > Something like:
> > "socionext,uniphier-pro4-usb3-reset", "socionext,uniphier-pro4-glue-reset" - for USB3 SoC AHCI
> > "socionext,uniphier-pro4-ahci-reset", "socionext,uniphier-pro4-glue-reset" - for Pro4 SoC AHCI
> >
> > That way if more places turn up where the glue layer reset is used,
> > you can add them without patching the driver every time.
> 
> 
> This is a trade-off between "patch the driver"
> and "potential change of the binding".

Adding "glue-reset" is usable for devices having same parent clocks/resets as
usb3/ahci, and we can add the devices without patches.

However, if the device needs other parent clocks/resets for the same SoC,
we can't add "glue-reset" and we might add patches for the device as a result.
In this case, the "glue-reset" will become difficult to understand.


> There is no real hardware like pro4-glue-reset.
>
> I am guessing this is a part of syscon or something,
> but I cannot find any explanation in a bigger picture.
> 
> So, I cannot judge this further more.

Since it's hard to lead the best result,
currently I'd like to suggest the current compatibles, with "simple-reset"
if necessary.

Thank you,

---
Best Regards,
Kunihiko Hayashi