Message-ID: <54FF4413.90001@ti.com>
Date:	Tue, 10 Mar 2015 14:20:51 -0500
From:	Nishanth Menon <nm@...com>
To:	Tony Lindgren <tony@...mide.com>
CC:	Linus Walleij <linus.walleij@...aro.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Linux-OMAP <linux-omap@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Lokesh Vutla <lokeshvutla@...com>
Subject: Re: [PATCH 1/2] pinctrl: bindings: pinctrl: Add support for TI's
 IODelay configuration

On 03/10/2015 01:33 PM, Nishanth Menon wrote:
> On 03/10/2015 12:31 PM, Tony Lindgren wrote:
>> * Nishanth Menon <nm@...com> [150310 10:25]:
>>> On 03/10/2015 10:33 AM, Tony Lindgren wrote:
>>>> * Linus Walleij <linus.walleij@...aro.org> [150310 03:39]:
>>>>> On Wed, Mar 4, 2015 at 1:00 AM, Nishanth Menon <nm@...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@...03400 {
>         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@...4a000 {
>         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?
> 

a and g delays are in pico seconds parsed by iodelay driver, so,
revising proposal (and dropping the macros) to something as follows:


 pinctrl-1 =
 	&mmc2_pins_default,	/* points to mmc control core pins */
 	<&iodelay IODELAY_OFFSET(0x18c) 0 120>,       /* CFG_GPMC_A19_IN */
 	<&iodelay IODELAY_OFFSET(0x1a4) 265 360>,     /* CFG_GPMC_A20_IN */
 	<&iodelay IODELAY_OFFSET(0x1b0) 0 120>,       /* CFG_GPMC_A21_IN */
 	<&iodelay IODELAY_OFFSET(0x1bc) 0 120>,       /* CFG_GPMC_A22_IN */
 	<&iodelay IODELAY_OFFSET(0x1c8) 287 420>,     /* CFG_GPMC_A23_IN */
 	<&iodelay IODELAY_OFFSET(0x1d4) 144 240>,     /* CFG_GPMC_A24_IN */
 	<&iodelay IODELAY_OFFSET(0x1e0) 0 0>,         /* CFG_GPMC_A25_IN */
 	<&iodelay IODELAY_OFFSET(0x1ec) 120 0>,       /* CFG_GPMC_A26_IN */
 	<&iodelay IODELAY_OFFSET(0x1f8) 120 180>,     /* CFG_GPMC_A27_IN */
 	<&iodelay IODELAY_OFFSET(0x360) 0 0>;         /* CFG_GPMC_CS1_IN */

it might just need us to define the right parse path etc.. but should
let us scale with other phandle implementations as well.

offsets are computed by a macro IODELAY_OFFSET() -> just throwing in
an example set of values for illustration here.. but just to get the idea.


Will be nice to have some comments before I go down this path. Thanks
for helping review this to a reasonable direction.

-- 
Regards,
Nishanth Menon
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