linux-kernel - Re: [PATCH] hte: tegra194: improve the GPIO-related comment

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Message-ID: <7766de61-a046-3e17-1322-28bd7f1e61da@nvidia.com>
Date:   Mon, 2 Oct 2023 09:27:45 -0700
From:   Dipen Patel <dipenp@...dia.com>
To:     Bartosz Golaszewski <brgl@...ev.pl>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        timestamp@...ts.linux.dev, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH] hte: tegra194: improve the GPIO-related comment

On 10/2/23 1:33 AM, Bartosz Golaszewski wrote:
> On Fri, Sep 29, 2023 at 11:38 PM Dipen Patel <dipenp@...dia.com> wrote:
>>
>> On 9/11/23 2:44 AM, Bartosz Golaszewski wrote:
>>> From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
>>>
>>> Using any of the GPIO interfaces using the global numberspace is
>>> deprecated. Make it clear in the comment.
>>>
>>> Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
>>> Acked-by: Linus Walleij <linus.walleij@...aro.org>
>>> ---
>>> This was part of a wider series but since this is independent, I'm sending
>>> it separately.
>>>
>>>  drivers/hte/hte-tegra194.c | 13 ++++++++-----
>>>  1 file changed, 8 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/hte/hte-tegra194.c b/drivers/hte/hte-tegra194.c
>>> index 6fe6897047ac..9fd3c00ff695 100644
>>> --- a/drivers/hte/hte-tegra194.c
>>> +++ b/drivers/hte/hte-tegra194.c
>>> @@ -407,12 +407,15 @@ static int tegra_hte_line_xlate(struct hte_chip *gc,
>>>               return -EINVAL;
>>>
>>>       /*
>>> +      * GPIO consumers can access GPIOs in two ways:
>>>        *
>>> -      * There are two paths GPIO consumers can take as follows:
>>> -      * 1) The consumer (gpiolib-cdev for example) which uses GPIO global
>>> -      * number which gets assigned run time.
>>> -      * 2) The consumer passing GPIO from the DT which is assigned
>>> -      * statically for example by using TEGRA194_AON_GPIO gpio DT binding.
>>> +      * 1) Using the global GPIO numberspace.
>>> +      *
>>> +      * This is the old, now DEPRECATED method and should not be used in
>>> +      * new code. TODO: Check if tegra is even concerned by this.
>> This use case is to do namespace mapping from gpio subsystem to hte. Few doubts:
>> 1. What does deprecate mean here? Does gpio subsys not use global space anymore?
> 
> It does but we don't want to expose this to external users in any way
> anymore (and haven't to for years). This is what deprecated means.
> Users should deal with opaque GPIO descriptors not global GPIO
> numberspace.
> 
>> 2. If yes, what GPIO number is set when it comes from gpiolib-cdev, as based on that I may have to
>> reflect in the mapping, tegra194_aon_gpio_map for example.
> 
> Why DO you have to use a GPIO number though? If HTE needs just a
> number from some HTE numberspace (which in itself may be unnecessary)
> then why not just keep a local IDA for it? Do you have to know the
> GPIOs internal numbering scheme to make it work?

humm, overall, I just need to know which GPIO it is, for example, GPIO controller X Port A GPIO number 3
to do proper mapping.
Continuing from above example, the hte driver gets:
- GPIO Controller X from DT node
- the rest details in current code gets it from [1] and [2]

If there is alternate method exists, I would like to explore. I think IDA will not help in this case as ID assigned
does not hold meaning in this context.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpio/gpiolib-cdev.c?h=v6.6-rc3#n760
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/hte/hte-tegra194.c?h=v6.6-rc3#n421

> 
> Bart
> 
>>> +      *
>>> +      * 2) Using GPIO descriptors that can be assigned to consumer devices
>>> +      * using device-tree, ACPI or lookup tables.
>>>        *
>>>        * The code below addresses both the consumer use cases and maps into
>>>        * HTE/GTE namespace.
>>