Date:   Wed, 31 May 2017 15:58:27 +0800
From:   Baolin Wang <baolin.wang@...eadtrum.com>
To:     Linus Walleij <linus.walleij@...aro.org>
CC:     Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Baolin Wang <baolin.wang@...aro.org>
Subject: Re: [PATCH 1/2] DT: pinctrl: Add binding documentation for
 Spreadtrum pin controller

Hi Linus,

On 一,  5月 29, 2017 at 06:18:29下午 +0200, Linus Walleij wrote:
> On Sat, May 27, 2017 at 7:56 AM, Baolin Wang <baolin.wang@...eadtrum.com> wrote:
> 
> > This patch adds the binding documentation for Spreadtrum SC9860 pin
> > controller device.
> >
> > Signed-off-by: Baolin Wang <baolin.wang@...eadtrum.com>
> (...)
> 
> > +* Spreadtrum Pin Controller
> > +
> > +The Spreadtrum pin controller are organized in 3 blocks (types).
> > +
> > +The first block comprises some global control registers, and each
> > +register contains several feilds with one bit or several bits to
> 
> feilds -> fields

Sorry for typos, will fix in next version.

> 
> Do you mean "bitfields", i.e a few bits inside a configuration register
> word?

Yes.

> 
> > +configurate for some global common configuration, such as domain
> 
> configurate -> configure

OK.

> 
> > +pad driving level, system control select
> 
> Actually I do not understand at all what "domain pad driving level"
> or "system control select" means, those are very generic terms.
> Can you describe precisely what it means? What domain? What
> is a domain pad? What kind of system control? What is it selecting
> between?

I try to explain what they are on Spreadtrum platform. One pin can output
3.0v or 1.8v, depending on the related domain pad driving selection, if
the related domain pad slect 3.0v, then the pin can output 3.0v.

"system control" is used to choose this function (like: UART0) for which
system, since we have several systems (AP/CP/CM4) on one SoC.

> 
> >  and so on. We recognise
> > +every feild comprising one bit or several bits in one global control
> 
> feild -> field
> 
> > +register as one pin, thus we should record every pin's bit offset,
> > +bit width and register offset to configurate this feild (pin).
> 
> feild -> field
> 
> > +The second block comprises some common registers which have unified
> > +register definition, and each register described one pin is used
> > +to configurate pin sleep mode and function select.
> 
> OK
> 
> > +The last block comprises some misc registers which also have unified
> > +register definition, and each register described one pin is used to
> > +configurate drive strength, pull up/down and so on.
> 
> configurate -> configure
> 
> OK that is pin configuration.
> 
> > +This driver supports the generic pin multiplexing and configuration
> > +bindings. For details on each properties, you can refer to
> > +./pinctrl-bindings.txt.
> 
> Do not talk about the driver in the bindings. Talk about the bindings per
> se, these bindings are supposed to be OS neutral.

Sure, will remove these.

> 
> > +Required properties for Spreadtrum pin controller:
> > +- compatible: "sprd,<soc>-pinctrl"
> > +  Please refer to each sprd,<soc>-pinctrl.txt binding doc for supported SoCs.
> > +
> > +Required properties for pin configuration node:
> > +- sprd,pins: each entry consists of 2 integers and represents the pin
> > +  id and config setting for one pin.
> 
> Do not use the custom property "sprd,pins" for this, if you want to set up pin
> muxing with a magic value use the generic binding "pinmux", see:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt?id=8d5e7c5df0a6c442373628be5221321172b1badf
> 
> But consider using groups+functions for defining multiplexing instead.
> 
> But please do NOT combine pin configuration into a magic value. Use
> the generic pin control bindings, er have bindings for all kinds of pin
> config, and using them makes the driver much more readable for
> humans.
> 
> I understand that you may have a lot of magic number tables around that
> you are using today, but it is necessary to decompose that into the proper
> generic pin configuration properties to make it usable.

Since we have lots of different pin configuration to set, it will be hard to
use the standard pin config describing in binding files. But I will try to
remove the magic number and use the common pin config.

> 
> > +++ b/Documentation/devicetree/bindings/pinctrl/sprd,sc9860-pinctrl.txt
> > @@ -0,0 +1,26 @@
> > +* Spreadtrum SC9860 Pin Controller
> > +
> > +Please refer to sprd,pinctrl.txt in this directory for common binding part
> > +and usage.
> > +
> > +Required properties:
> > +- compatible: must be "sprd,sc9860-pinctrl".
> > +- reg: the register address of pin controller device.
> > +- sprd,pins: two integers array, represents a group of pins id and config
> > +  setting. The format is sprd,pins = <PIN_ID CONFIG>, PIN_ID can be found
> > +  from pinctrl-sprd-sc9860.c file or spec file, CONFIG is the pad setting
> > +  value like pull-up for this pin.
> 
> Same comments.
> 
> > +Example:
> > +pin_controller: pinctrl@...a0000 {
> > +       compatible = "sprd,sc9860-pinctrl";
> > +       reg = <0x402a0000 0x10000>;
> > +
> > +       vio_sd0_ms_0: sd0_ms0 {
> > +               sprd,pins = <8 0x1>;
> > +       };
> > +
> > +       vbc_iis0_0: iis0_c {
> > +               sprd,pins = <34 0xc>;
> > +       };
> > +};
> 
> Magic numbers are very hard to understand. Compare to this
> from Qualcomm APQ8064 using just standard bindings:
> 
> pinmux@...000 {
>         i2c4_pins: i2c4_pinmux {
>                pins = "gpio12", "gpio13";
>                function = "gsbi4";
>                bias-disable;
>         };
> 
>         spi_pins: spi_pins {
>                mux {
>                       pins = "gpio18", "gpio19", "gpio21";
>                       function = "gsbi5";
>                       drive-strength = <10>;
>                       bias-none;
>                 };
>         };
> };
> 
> Please try go get rid of the magic numbers and get to use pins, function,
> drive-strength bias etc from the standard bindings. We also have a lot
> of helper code available to use this.

Sure. I will try o fix this. Thanks for your helpful comments.

> 
> Yours,
> Linus Walleij

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