linux-kernel - Re: [v6 2/4] dt-bindings: hwmon: Add ASPEED TACH Control documentation

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Message-ID: <CAGUgbhDmXnyxYCL9h9C0P4ByDSTstWnGqW=uFoDVVHeK3BerHA@mail.gmail.com>
Date:   Tue, 18 Jul 2023 12:01:13 +0800
From:   蔡承達 <billyking19920205@...il.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        "jdelvare@...e.com" <jdelvare@...e.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "joel@....id.au" <joel@....id.au>,
        "andrew@...id.au" <andrew@...id.au>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        "u.kleine-koenig@...gutronix.de" <u.kleine-koenig@...gutronix.de>,
        "corbet@....net" <corbet@....net>,
        "p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "patrick@...cx.xyz" <patrick@...cx.xyz>,
        Billy Tsai <billy_tsai@...eedtech.com>
Subject: Re: [v6 2/4] dt-bindings: hwmon: Add ASPEED TACH Control documentation

>
> On 17/07/2023 11:01, 蔡承達 wrote:
> > Guenter Roeck <linux@...ck-us.net> 於 2023年7月17日 週一 上午1:00寫道：
> >>
> >> On 7/16/23 09:08, Krzysztof Kozlowski wrote:
> >>
> >> [ ... ]
> >>
> >>>>
> >>>> This patch serial doesn't use to binding the fan control h/w. It is
> >>>> used to binding the two independent h/w blocks.
> >>>> One is used to provide pwm output and another is used to monitor the
> >>>> speed of the input.
> >>>> My patch is used to point out that the pwm and the tach is the
> >>>> different function and don't need to
> >>>> bind together. You can not only combine them as the fan usage but also
> >>>> treat them as the individual module for
> >>>> use. For example: the pwm can use to be the beeper (pwm-beeper.c), the
> >>>> tach can be used to monitor the heart beat signal.
> >>>
> >>> Isn't this exactly the same as in every other SoC? PWMs can be used in
> >>> different ways?
> >>>
> >>
> >> ... and in every fan controller. Not that it really makes sense because
> >> normally the pwm controller part of such chips is tied to the fan input,
> >> to enable automatic fan control, but it is technically possible.
> >> In many cases this is also the case in SoCs, for example, in ast2500.
> >> Apparently this was redesigned in ast2600 where they two blocks are
> >> only lightly coupled (there are two pwm status bits in the fan status
> >> register, but I have no idea what those mean). If the blocks are tightly
> >> coupled, separate drivers don't really make sense.
> >>
> >> There are multiple ways to separate the pwm controller part from the
> >> fan inputs if that is really necessary. One would be to provide a
> >> sequence of address mappings, the other would be to pass the memory
> >> region from an mfd driver. It is not necessary to have N instances
> >> of the fan controller, even if the address space is not continuous.
> >>
> >
> > Hi Guenter,
> >
> > May I ask about the meaning of the sequence of address mappings? It appears
> > to consist of multiple tuples within the 'reg' property, indicating
> > the usage of PWM/Tach
> > registers within a single instance. After that I can use the dts like following:
> >
> > pwm: pwm@...10000 {
> > ...
> > reg = <0x1e610000 0x8
> > 0x1e610010 0x8
> > 0x1e610020 0x8
> > 0x1e610030 0x8
> > 0x1e610040 0x8
> > 0x1e610050 0x8
> > 0x1e610060 0x8
> > 0x1e610070 0x8
> > 0x1e610080 0x8
> > 0x1e610090 0x8
> > 0x1e6100A0 0x8
> > 0x1e6100B0 0x8
> > 0x1e6100C0 0x8
> > 0x1e6100D0 0x8
> > 0x1e6100E0 0x8
> > 0x1e6100F0 0x8>;
>
>
> Uh, no... I mean, why? We keep pointing out that this should not be done
> differently than any other SoC. Open any other SoC PWM controller and
> tell me why this is different? Why this cannot be one address space?

Hi Krzysztof,

This is because the register layout for PWM and Tach is not continuous.
Each PWM/Tach instance has its own set of controller registers, and they
are independent of each other.

For example:
PWM0 uses registers 0x0 and 0x4, while Tach0 uses registers 0x8 and 0xc.
PWM1 uses registers 0x10 and 0x14, while Tach1 uses registers 0x18 and 0x1c.
...

To separate the PWM controller part from the fan inputs, Guenter has
provided two methods.
The first method involves passing the memory region from an MFD
driver, which was the
initial method I intended to use. However, it seems that this method
does not make sense to you.

Therefore, I would like to explore the second method suggested by
Guenter, which involves providing
a sequence of address mappings.

Thanks

Best Regards,
Billy Tsai