[2/4] pinctrl: Add skew-delay pin config and bindings

Message ID 20171028133719.27528-2-linus.walleij@linaro.org
State New
Headers show
Series
  • [1/4] pinctrl: gemini: Add missing functions
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Commit Message

Linus Walleij Oct. 28, 2017, 1:37 p.m.
Some pin controllers (such as the Gemini) can control the
expected clock skew and output delay on certain pins with a
sub-nanosecond granularity. This is typically done by shunting
in a number of double inverters in front of or behind the pin.
Make it possible to configure this with a generic binding.

Cc: devicetree@vger.kernel.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
---
 Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt | 4 ++++
 drivers/pinctrl/pinconf-generic.c                              | 2 ++
 include/linux/pinctrl/pinconf-generic.h                        | 5 +++++
 3 files changed, 11 insertions(+)

Comments

Hans Ulli Kroll Nov. 1, 2017, 5:56 a.m. | #1
Hi Linus,

On Sat, 28 Oct 2017, Linus Walleij wrote:

> Some pin controllers (such as the Gemini) can control the
> expected clock skew and output delay on certain pins with a
> sub-nanosecond granularity. This is typically done by shunting
> in a number of double inverters in front of or behind the pin.
> Make it possible to configure this with a generic binding.
> 
> Cc: devicetree@vger.kernel.org
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---

Acked-by: Hans Ulli Kroll <ulli.kroll@googlemail.com>

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Rob Herring Nov. 1, 2017, 9:26 p.m. | #2
On Sat, Oct 28, 2017 at 03:37:17PM +0200, Linus Walleij wrote:
> Some pin controllers (such as the Gemini) can control the
> expected clock skew and output delay on certain pins with a
> sub-nanosecond granularity. This is typically done by shunting
> in a number of double inverters in front of or behind the pin.
> Make it possible to configure this with a generic binding.
> 
> Cc: devicetree@vger.kernel.org
> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
> ---
>  Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt | 4 ++++
>  drivers/pinctrl/pinconf-generic.c                              | 2 ++
>  include/linux/pinctrl/pinconf-generic.h                        | 5 +++++
>  3 files changed, 11 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt b/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
> index 4483cc31e531..ad9bbbba36e9 100644
> --- a/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
> +++ b/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
> @@ -271,6 +271,10 @@ output-high		- set the pin to output mode with high level
>  sleep-hardware-state	- indicate this is sleep related state which will be programmed
>  			  into the registers for the sleep state.
>  slew-rate		- set the slew rate
> +skew-delay		- this affects the expected clock skew on input pins
> +			  and the delay before latching a value to an output
> +			  pin. Typically indicates how many double-inverters are
> +			  used to delay the signal.

Units?

>  
>  For example:
>  
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Linus Walleij Nov. 2, 2017, 2:32 p.m. | #3
On Wed, Nov 1, 2017 at 10:26 PM, Rob Herring <robh@kernel.org> wrote:
> On Sat, Oct 28, 2017 at 03:37:17PM +0200, Linus Walleij wrote:
>> Some pin controllers (such as the Gemini) can control the
>> expected clock skew and output delay on certain pins with a
>> sub-nanosecond granularity. This is typically done by shunting
>> in a number of double inverters in front of or behind the pin.
>> Make it possible to configure this with a generic binding.
>>
>> Cc: devicetree@vger.kernel.org
>> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
>> ---
>>  Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt | 4 ++++
>>  drivers/pinctrl/pinconf-generic.c                              | 2 ++
>>  include/linux/pinctrl/pinconf-generic.h                        | 5 +++++
>>  3 files changed, 11 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt b/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
>> index 4483cc31e531..ad9bbbba36e9 100644
>> --- a/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
>> +++ b/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
>> @@ -271,6 +271,10 @@ output-high              - set the pin to output mode with high level
>>  sleep-hardware-state - indicate this is sleep related state which will be programmed
>>                         into the registers for the sleep state.
>>  slew-rate            - set the slew rate
>> +skew-delay           - this affects the expected clock skew on input pins
>> +                       and the delay before latching a value to an output
>> +                       pin. Typically indicates how many double-inverters are
>> +                       used to delay the signal.
>
> Units?

Number of double-inverters I guess, just as it says.

skew-delay = <1>; // number of inverter pairs

Like with other bindings of this type they are custom.

The Gemini datasheet says "every unit represents about 0.2 ns".

So if you set it to 1, that means (as far as I can guess) this
is shunted in:

   |\    |\
--+ >o--+ >o---
   |/    |/

The signal will take ~0.2 ns to propagate through this.
For 2, there will be four inverters etc.

It is dependent of production technology, and I do not know
if everyone is using something like double-inverters.

We could try to define a value in picoseconds instead so I
would need to set this to 200 in that case if you think that is better:

skew-delay = <200>; // picoseconds

I think it would be kludgy since with increasing clock speeds
maybe picoseconds would be too big even. Nanoseconds is
apparently already a to coarse unit.

Yours,
Linus Walleij
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Rob Herring Nov. 8, 2017, 12:38 a.m. | #4
On Thu, Nov 2, 2017 at 9:32 AM, Linus Walleij <linus.walleij@linaro.org> wrote:
> On Wed, Nov 1, 2017 at 10:26 PM, Rob Herring <robh@kernel.org> wrote:
>> On Sat, Oct 28, 2017 at 03:37:17PM +0200, Linus Walleij wrote:
>>> Some pin controllers (such as the Gemini) can control the
>>> expected clock skew and output delay on certain pins with a
>>> sub-nanosecond granularity. This is typically done by shunting
>>> in a number of double inverters in front of or behind the pin.
>>> Make it possible to configure this with a generic binding.
>>>
>>> Cc: devicetree@vger.kernel.org
>>> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
>>> ---
>>>  Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt | 4 ++++
>>>  drivers/pinctrl/pinconf-generic.c                              | 2 ++
>>>  include/linux/pinctrl/pinconf-generic.h                        | 5 +++++
>>>  3 files changed, 11 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt b/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
>>> index 4483cc31e531..ad9bbbba36e9 100644
>>> --- a/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
>>> +++ b/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
>>> @@ -271,6 +271,10 @@ output-high              - set the pin to output mode with high level
>>>  sleep-hardware-state - indicate this is sleep related state which will be programmed
>>>                         into the registers for the sleep state.
>>>  slew-rate            - set the slew rate
>>> +skew-delay           - this affects the expected clock skew on input pins
>>> +                       and the delay before latching a value to an output
>>> +                       pin. Typically indicates how many double-inverters are
>>> +                       used to delay the signal.
>>
>> Units?
>
> Number of double-inverters I guess, just as it says.
>
> skew-delay = <1>; // number of inverter pairs
>
> Like with other bindings of this type they are custom.
>
> The Gemini datasheet says "every unit represents about 0.2 ns".
>
> So if you set it to 1, that means (as far as I can guess) this
> is shunted in:
>
>    |\    |\
> --+ >o--+ >o---
>    |/    |/
>
> The signal will take ~0.2 ns to propagate through this.
> For 2, there will be four inverters etc.
>
> It is dependent of production technology, and I do not know
> if everyone is using something like double-inverters.
>
> We could try to define a value in picoseconds instead so I
> would need to set this to 200 in that case if you think that is better:
>
> skew-delay = <200>; // picoseconds
>
> I think it would be kludgy since with increasing clock speeds
> maybe picoseconds would be too big even. Nanoseconds is
> apparently already a to coarse unit.

Okay, it is fine.

Acked-by: Rob Herring <robh@kernel.org>
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Patch

diff --git a/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt b/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
index 4483cc31e531..ad9bbbba36e9 100644
--- a/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
+++ b/Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
@@ -271,6 +271,10 @@  output-high		- set the pin to output mode with high level
 sleep-hardware-state	- indicate this is sleep related state which will be programmed
 			  into the registers for the sleep state.
 slew-rate		- set the slew rate
+skew-delay		- this affects the expected clock skew on input pins
+			  and the delay before latching a value to an output
+			  pin. Typically indicates how many double-inverters are
+			  used to delay the signal.
 
 For example:
 
diff --git a/drivers/pinctrl/pinconf-generic.c b/drivers/pinctrl/pinconf-generic.c
index 8eaa25c3384f..b4f7f8a458ea 100644
--- a/drivers/pinctrl/pinconf-generic.c
+++ b/drivers/pinctrl/pinconf-generic.c
@@ -49,6 +49,7 @@  static const struct pin_config_item conf_items[] = {
 	PCONFDUMP(PIN_CONFIG_POWER_SOURCE, "pin power source", "selector", true),
 	PCONFDUMP(PIN_CONFIG_SLEEP_HARDWARE_STATE, "sleep hardware state", NULL, false),
 	PCONFDUMP(PIN_CONFIG_SLEW_RATE, "slew rate", NULL, true),
+	PCONFDUMP(PIN_CONFIG_SKEW_DELAY, "skew delay", NULL, true),
 };
 
 static void pinconf_generic_dump_one(struct pinctrl_dev *pctldev,
@@ -181,6 +182,7 @@  static const struct pinconf_generic_params dt_params[] = {
 	{ "power-source", PIN_CONFIG_POWER_SOURCE, 0 },
 	{ "sleep-hardware-state", PIN_CONFIG_SLEEP_HARDWARE_STATE, 0 },
 	{ "slew-rate", PIN_CONFIG_SLEW_RATE, 0 },
+	{ "skew-delay", PIN_CONFIG_SKEW_DELAY, 0 },
 };
 
 /**
diff --git a/include/linux/pinctrl/pinconf-generic.h b/include/linux/pinctrl/pinconf-generic.h
index 5d8bc7f21c2a..ec6dadcc1fde 100644
--- a/include/linux/pinctrl/pinconf-generic.h
+++ b/include/linux/pinctrl/pinconf-generic.h
@@ -90,6 +90,10 @@ 
  * @PIN_CONFIG_SLEW_RATE: if the pin can select slew rate, the argument to
  *	this parameter (on a custom format) tells the driver which alternative
  *	slew rate to use.
+ * @PIN_CONFIG_SKEW_DELAY: if the pin has programmable skew rate (on inputs)
+ *	or latch delay (on outputs) this parameter (in a custom format)
+ *	specifies the clock skew or latch delay. It typically controls how
+ *	many double inverters are put in front of the line.
  * @PIN_CONFIG_END: this is the last enumerator for pin configurations, if
  *	you need to pass in custom configurations to the pin controller, use
  *	PIN_CONFIG_END+1 as the base offset.
@@ -117,6 +121,7 @@  enum pin_config_param {
 	PIN_CONFIG_POWER_SOURCE,
 	PIN_CONFIG_SLEEP_HARDWARE_STATE,
 	PIN_CONFIG_SLEW_RATE,
+	PIN_CONFIG_SKEW_DELAY,
 	PIN_CONFIG_END = 0x7F,
 	PIN_CONFIG_MAX = 0xFF,
 };