linux-kernel - Re: [RFC v1 1/2] scmi: Introduce pinctrl SCMI protocol driver

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Date:   Fri, 21 Apr 2023 10:47:49 +0100
From:   Cristian Marussi <cristian.marussi@....com>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Oleksii Moisieiev <Oleksii_Moisieiev@...m.com>,
        Peng Fan <peng.fan@....nxp.com>,
        "sudeep.holla@....com" <sudeep.holla@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "michal.simek@....com" <michal.simek@....com>,
        "vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
        "souvik.chakravarty@....com" <souvik.chakravarty@....com>
Subject: Re: [RFC v1 1/2] scmi: Introduce pinctrl SCMI protocol driver

On Fri, Apr 21, 2023 at 11:28:38AM +0200, Linus Walleij wrote:
> On Fri, Apr 21, 2023 at 10:40 AM Oleksii Moisieiev
> <Oleksii_Moisieiev@...m.com> wrote:
> > On 17.04.23 05:55, Peng Fan wrote:
> > > On 4/13/2023 6:04 AM, Cristian Marussi wrote:
> 
> > > Is it possible to extend the spec to support multilple uint32_t for PIN
> > > CONFIG SET?
> > >
> > > With only one uint32_t could not satisfy i.MX requirement.
> > >
> > > Thanks,
> > > Peng.
> > >
> > IIUC you are expecting to have an ability to set some kind of array of
> > uint32_t config values to some specific ConfigType?
> >
> > I'm not sure if it's supported by pintctrl subsystem right now. I was
> > unable to find an example in the existing device-tree pinctrl bindings.
> > This makes me think that this kind of binding is OEM specific.
> >
> > Maybe it can be implemented by adding new IDs to OEM specific range
> > (192-255) which is reserved for OEM specific units (See Table 23 of
> > DEN0056E).
> 

Hi Linus,

> From a pinctrl point of view I do not understand this requirement.
> 
> The pinctrl subsystem in the Linux kernel certainly does not support
> an array of u32 for the pin config, we only support passing a single
> u32 value along with the enumerator (config type), or well it is
> actually 24 bits in Linux, the uppermost 8 bits is for the config type:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/pinctrl/pinconf-generic.h
> 
> /*
>  * Helpful configuration macro to be used in tables etc.
>  */
> #define PIN_CONF_PACKED(p, a) ((a << 8) | ((unsigned long) p & 0xffUL))
> 
> p = parameter (PIN_CONFIG_DRIVE_STRENGTH etc)
> a = argument (value such as in mA)
> 

My (possibly wrong) reasoning on the other reply, is based on the
(possibly equally wrong :D) understanding that what Peng wants is just
the possibility at the spec and the SCMI protocol layer (exposed in
protocol operations) to issue PINCTRL_SET requests containing optionally
an array of multiple ConfigType/Value pairs (which is anyway not supported
by PinCtrl as I understand) instead of a single pair.

... but I can divine (:D)....that soon a new SCMI spec review/comment/amend
cycle will be coming for people reading this...

Thanks,
Cristian