linux-kernel - Re: [PATCH v2 1/2] pinctrl: qcom: Add egpio feature support

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Date:   Tue, 2 Nov 2021 16:08:53 +0530
From:   Rajendra Nayak <rnayak@...eaurora.org>
To:     Stephen Boyd <swboyd@...omium.org>, agross@...nel.org,
        bjorn.andersson@...aro.org, linus.walleij@...aro.org
Cc:     linux-arm-msm@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org, psodagud@...eaurora.org,
        dianders@...omium.org
Subject: Re: [PATCH v2 1/2] pinctrl: qcom: Add egpio feature support


On 10/30/2021 12:35 AM, Stephen Boyd wrote:
> Quoting Rajendra Nayak (2021-10-29 03:19:04)
>>
>>
>> On 10/29/2021 12:24 PM, Stephen Boyd wrote:
>>> Quoting Rajendra Nayak (2021-10-26 05:07:35)
>>>> From: Prasad Sodagudi <psodagud@...eaurora.org>
>>>>
>>>> egpio is a scheme which allows special power Island Domain IOs
>>>> (LPASS,SSC) to be reused as regular chip GPIOs by muxing regular
>>>> TLMM functions with Island Domain functions.
>>>> With this scheme, an IO can be controlled both by the cpu running
>>>> linux and the Island processor. This provides great flexibility to
>>>> re-purpose the Island IOs for regular TLMM usecases.
>>>>
>>>> 2 new bits are added to ctl_reg, egpio_present is a read only bit
>>>> which shows if egpio feature is available or not on a given gpio.
>>>> egpio_enable is the read/write bit and only effective if egpio_present
>>>> is 1. Once its set, the Island IO is controlled from Chip TLMM.
>>>> egpio_enable when set to 0 means the GPIO is used as Island Domain IO.
>>>>
>>>> To support this we add a new function 'egpio' which can be used to
>>>> set the egpio_enable to 0, for any other TLMM controlled functions
>>>> we set the egpio_enable to 1.
>>>>
>>>> Signed-off-by: Prasad Sodagudi <psodagud@...eaurora.org>
>>>> Signed-off-by: Rajendra Nayak <rnayak@...eaurora.org>
>>>> ---
>>>
>>> Does this supersede adding support for lpass pinctrl in this series[1]?
>>
>> No, the driver in [1] actually manages the LPASS TLMM instance, while this patch
>> makes it possible for the 'same' pins to be managed by the SoC TLMM instance.
>> On sc7280 SoC for instance GPIO144-158 maps to LPI-GPIO-0-14, and GPIO159-174
>> maps to SSC-GPIO-0-15.
> 
> How do we make sure that the LPASS pins are actually muxed out of the
> SoC and not blocked by eGPIO in this driver muxing out the pin as a
> gpio? Do they avoid conflicting with each other somehow?

No, currently they don't. The default value of egpio_enable is 0, so
if SoC TLMM grabs it first and sets it to 1 and then the LPASS TLMM tries
to grab it, perhaps it can find out and throw and error, though I don;t
think it does that today.
I am not sure how this can be caught when its the other way round (LPASS grabs it first)

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