Re: [PATCH 1/2] pinctrl: bindings: pinctrl: Add support for TI's IODelay configuration

From: Nishanth Menon <nm@ti.com>
To: Tony Lindgren <tony@atomide.com>
Cc: Linus Walleij <linus.walleij@linaro.org>,
	"linux-gpio@vger.kernel.org" <linux-gpio@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
	Linux-OMAP <linux-omap@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	Lokesh Vutla <lokeshvutla@ti.com>
Subject: Re: [PATCH 1/2] pinctrl: bindings: pinctrl: Add support for TI's IODelay configuration
Date: Tue, 10 Mar 2015 13:33:23 -0500	[thread overview]
Message-ID: <54FF38F3.2030703@ti.com> (raw)
In-Reply-To: <20150310173115.GS5264@atomide.com>

On 03/10/2015 12:31 PM, Tony Lindgren wrote:
> * Nishanth Menon <nm@ti.com> [150310 10:25]:
>> On 03/10/2015 10:33 AM, Tony Lindgren wrote:
>>> * Linus Walleij <linus.walleij@linaro.org> [150310 03:39]:
>>>> On Wed, Mar 4, 2015 at 1:00 AM, Nishanth Menon <nm@ti.com> wrote:
>>>>
>>>>> +Configuration definition follows similar model as the pinctrl-single:
>>>>> +The groups of pin configuration are defined under "pinctrl-single,pins"
>>>>> +
>>>>> +&dra7_iodelay_core {
>>>>> +       mmc2_iodelay_3v3_conf: mmc2_iodelay_3v3_conf {
>>>>> +               pinctrl-single,pins = <
>>>>> +                       0x18c (A_DELAY(0) | G_DELAY(120))       /* CFG_GPMC_A19_IN */
>>>>> +                       0x1a4 (A_DELAY(265) | G_DELAY(360))     /* CFG_GPMC_A20_IN */
>>>>> +                       0x1b0 (A_DELAY(0) | G_DELAY(120))       /* CFG_GPMC_A21_IN */
>>>>> +                       0x1bc (A_DELAY(0) | G_DELAY(120))       /* CFG_GPMC_A22_IN */
>>>>> +                       0x1c8 (A_DELAY(287) | G_DELAY(420))     /* CFG_GPMC_A23_IN */
>>>>> +                       0x1d4 (A_DELAY(144) | G_DELAY(240))     /* CFG_GPMC_A24_IN */
>>>>> +                       0x1e0 (A_DELAY(0) | G_DELAY(0))         /* CFG_GPMC_A25_IN */
>>>>> +                       0x1ec (A_DELAY(120) | G_DELAY(0))       /* CFG_GPMC_A26_IN */
>>>>> +                       0x1f8 (A_DELAY(120) | G_DELAY(180))     /* CFG_GPMC_A27_IN */
>>>>> +                       0x360 (A_DELAY(0) | G_DELAY(0))         /* CFG_GPMC_CS1_IN */
>>>>> +               >;
>>>>> +       };
>>>>> +};
>>>>
>>>> But wait.
>>>>
>>>> The promise when we merged pinctrl-single was that this driver was to be used
>>>> when the system had a one-register-per-pin layout and it was easy to do device
>>>> trees based on that.
>>>>
>>>> We were very reluctant to accept that even though we didn't even have the
>>>> generic pin control bindings in place, the argument being that the driver
>>>> should know the detailed register layout, it should not be described in the
>>>> device tree. We eventually caved in and accepted it as an exception.
>>>
>>> Hey let's get few things straight here. There's nothing stopping the
>>> driver from knowing a detailed register layout with the pinctrl-single
>>> binding. This can be very easily done based on the compatible flag and
>>> match data as needed and check the values provided.
>>>
>>> And let's also recap the reasons for the pinctrl-single binding. The
>>> the main reason for the pinctrl-single binding is to avoid mapping
>>> individual register bits to device tree compatible string properties.
>>>
>>> Imagine doing that for hundreds of similar registers. Believe me, I tried
>>> using device tree properties initially and it just sucked big time. For
>>> larger amounts of dts data, it's best to stick to numeric values and
>>> phandles in the device tree data and rely on the preprocessor for
>>> getting the values right.
>>>
>>> Finally, we don't want to build databases into the kernel drivers for
>>> every SoC. We certainly have plenty fo those already.
>>>  
>>>> Since this pin controller is not using pinctrl-single it does not enjoy that
>>>> privilege and you need to explain why this pin controller cannot use the
>>>> generic bindings like so many other pin controllers have since started
>>>> to do. ("It is in the same SoC" is not an acceptable argument.)
>>>>
>>>> What is wrong with this:
>>>> Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
>>>
>>> Nishanth, care to explain your reasons for using pinctrl-single binding
>>> here vs the generic binding? Is the amount of string parsing with the
>>> data an issue here?
>>
>> Wrong option chosen, I suppose :( - alright, lets discuss the alternative.
> 
> Heh well now we know :) 
>   
>>>> We can add generic delay bindings to the list, it even seems like
>>>> a good idea to do so, as it is likely something that will come up in
>>>> other hardware and will be needed for ACPI etc going forward.
>>>
>>> We certainly need to make setting delays (with values) generic, no
>>> doubt about that.
>>>
>>> If the large amount of data is not an issue here, we could maybe set
>>> each iodelay register as a separate device? Then the binding could
>>> be just along the interrupts-extended type binding:
>>>
>>> foo = <&bar 0x18c A_DELAY(0) G_DELAY(120)>;
>>>
>>> Where the 0x18c is the instance offset of the register within the
>>> ti,dra7-iodelay compatible controller.
>>
>> if mmc2_pins_default point at pins for mmc pin configuration for
>> control_core (pinctrl-single), are you proposing the following?
>>
>>  mmc2_pins_default: mmc2_pins_default {
>>          pinctrl-single,pins = <
>>                  0x9c (PIN_INPUT_PULLUP | MANUAL_MODE | MUX_MODE1) /*
>> gpmc_a23.mmc2_clk */
>>                  0xb0 (PIN_INPUT_PULLUP | MANUAL_MODE | MUX_MODE1) /*
>> gpmc_cs1.mmc2_cmd */
>>                  0xa0 (PIN_INPUT_PULLUP | MANUAL_MODE | MUX_MODE1) /*
>> gpmc_a24.mmc2_dat0 */
>>                  0xa4 (PIN_INPUT_PULLUP | MANUAL_MODE | MUX_MODE1) /*
>> gpmc_a25.mmc2_dat1 */
>>                  0xa8 (PIN_INPUT_PULLUP | MANUAL_MODE | MUX_MODE1) /*
>> gpmc_a26.mmc2_dat2 */
>>                  0xac (PIN_INPUT_PULLUP | MANUAL_MODE | MUX_MODE1) /*
>> gpmc_a27.mmc2_dat3 */
>>                  0x8c (PIN_INPUT_PULLUP | MANUAL_MODE | MUX_MODE1) /*
>> gpmc_a19.mmc2_dat4 */
>>                  0x90 (PIN_INPUT_PULLUP | MANUAL_MODE | MUX_MODE1) /*
>> gpmc_a20.mmc2_dat5 */
>>                  0x94 (PIN_INPUT_PULLUP | MANUAL_MODE | MUX_MODE1) /*
>> gpmc_a21.mmc2_dat6 */
>>                  0x98 (PIN_INPUT_PULLUP | MANUAL_MODE | MUX_MODE1) /*
>> gpmc_a22.mmc2_dat7 */
>>          >;
>>  };
> 
> Yeah so existing pinctrl-single binding above, with additional iodelay
> binding below..
>  
>> &mmc2 {
>> ...
>>  pinctrl-1 =
>>  	&mmc2_pins_default,	/* points to mmc control core pins */
>>  	<&iodelay 0x18c A_DELAY(0) | G_DELAY(120)>,       /* CFG_GPMC_A19_IN */
>>  	<&iodelay 0x1a4 A_DELAY(265) | G_DELAY(360)>,     /* CFG_GPMC_A20_IN */
>>  	<&iodelay 0x1b0 A_DELAY(0) | G_DELAY(120)>,       /* CFG_GPMC_A21_IN */
>>  	<&iodelay 0x1bc A_DELAY(0) | G_DELAY(120)>,       /* CFG_GPMC_A22_IN */
>>  	<&iodelay 0x1c8 A_DELAY(287) | G_DELAY(420)>,     /* CFG_GPMC_A23_IN */
>>  	<&iodelay 0x1d4 A_DELAY(144) | G_DELAY(240)>,     /* CFG_GPMC_A24_IN */
>>  	<&iodelay 0x1e0 A_DELAY(0) | G_DELAY(0)>,         /* CFG_GPMC_A25_IN */
>>  	<&iodelay 0x1ec A_DELAY(120) | G_DELAY(0)>,       /* CFG_GPMC_A26_IN */
>>  	<&iodelay 0x1f8 A_DELAY(120) | G_DELAY(180)>,     /* CFG_GPMC_A27_IN */
>>  	<&iodelay 0x360 A_DELAY(0) | G_DELAY(0)>;         /* CFG_GPMC_CS1_IN */
>>
>> I have to check if we are capable of parsing that. but if that is the
>> approach chosen, I suppose we might be able to figure something, I
>> suppose..
> 
> Yes except I'd make use of some kind of #pinctrl-cells here just like
> interrupt controller has #interrupt-cells. Then you can have the values
> seprate and the controller knows what to do with them based on the
> compatible flag and #pinctrl-cells.

Something like the following I suppose, where pinctrl-cells is optional?

dra7_pmx_core: pinmux@4a003400 {
        compatible = "ti,dra7-padconf", "pinctrl-single";
        reg = <0x4a003400 0x0464>;
        #address-cells = <1>;
        #size-cells = <0>;
        #interrupt-cells = <1>;
        interrupt-controller;
        pinctrl-single,register-width = <32>;
        pinctrl-single,function-mask = <0x3fffffff>;
};

dra7_iodelay_core: padconf@4844a000 {
        compatible = "ti,dra7-iodelay";
        reg = <0x4844a000 0x0d1c>;
        #address-cells = <1>;
        #size-cells = <0>;
	#pinctrl-cells = <2>;
};

Linus,

I hope you are ok with the above?

-- 
Regards,
Nishanth Menon