Re: IMX27: How to do 22k pull-up with the pinctrl ?

[Chris Ruehl <chris.ruehl-CR359r9tUDPXPF5Rlphj1Q@public.gmane.org>]

On Monday, November 11, 2013 10:29 PM, Linus Walleij wrote:
> On Mon, Nov 11, 2013 at 1:03 PM, Mark Rutland<mark.rutland-5wv7dgnIgG8@public.gmane.org>  wrote:
>> On Mon, Nov 11, 2013 at 10:45:30AM +0000, Chris Ruehl wrote:
>
>>> while I port the static code to the DT I step into the problem to
>>> set the PSCR for the sdhc2 ports to 22k pull-up
>>> I look for something like described in
>>>       pinctrl/fsl,imx-pinctrl.txt
>>>
>>> the fsl,imx27-pinctrl only say 0/1 dis/enable pull up but not the strength.
>
> So in the generic pin configuration, which we nowadays recommend new
> platforms to use, there is this (include/linux/pinctrl/pinconf-generic):
>
>   * @PIN_CONFIG_BIAS_PULL_UP: the pin will be pulled up (usually with high
>   *      impedance to VDD). If the argument is != 0 pull-up is enabled,
>   *      if it is 0, pull-up is total, i.e. the pin is connected to VDD.
>   * @PIN_CONFIG_BIAS_PULL_DOWN: the pin will be pulled down (usually with high
>   *      impedance to GROUND). If the argument is != 0 pull-down is enabled,
>   *      if it is 0, pull-down is total, i.e. the pin is connected to GROUND.
>
> The idea was to extend that with an argument for the number of
> Ohms the day it was needed and supported by some platform.
>
> We would then use the bindings from
> Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
> by adding something like this:
>
> (...)
> bias-pull-up-ohms =<22000>;
> (...)
>
> So in the generic world it can be accomodated in a quite
> straight-forward way.
>
> When the i.MX pin control was added in v3.5 the generic
> pin config was available but it was opted to use another
> pattern. One way to solve this is to migrate i.MX to use the
> generic pin config, which is going to be hard work. But as
> a subsystem maintainer that is still what I would recommend.
>
> Yours,
> Linus Walleij

Hi Linus,
Thank you for that very interesting comment!

I agree with your idea to move the IMX code to that more generic solution, there 
are already different ways to setup the DT for imx27 vs. imx3x or imx6 etc. and 
its not going to be better, my guess!

Chris

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