linux-kernel - Re: [PATCH 1/6] wifi: ath9k: Obtain system GPIOS from descriptors

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Date: Thu, 01 Feb 2024 14:51:23 +0200
From: Kalle Valo <kvalo@...nel.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Linus Walleij <linus.walleij@...aro.org>,  Toke Høiland-Jørgensen
 <toke@...e.dk>,  Arend van Spriel <aspriel@...il.com>,  Franky Lin
 <franky.lin@...adcom.com>,  Hante Meuleman <hante.meuleman@...adcom.com>,
  Arnd Bergmann <arnd@...db.de>,  Lee Jones <lee@...nel.org>,  Brian Norris
 <briannorris@...omium.org>,  Srinivasan Raju <srini.raju@...elifi.com>,
  linux-wireless@...r.kernel.org,  linux-kernel@...r.kernel.org,
  brcm80211-dev-list.pdl@...adcom.com
Subject: Re: [PATCH 1/6] wifi: ath9k: Obtain system GPIOS from descriptors

Andy Shevchenko <andriy.shevchenko@...ux.intel.com> writes:

> On Wed, Jan 31, 2024 at 11:37:20PM +0100, Linus Walleij wrote:
>
>> The ath9k has an odd use of system-wide GPIOs: if the chip
>> does not have internal GPIO capability, it will try to obtain a
>> GPIO line from the system GPIO controller:
>> 
>>   if (BIT(gpio) & ah->caps.gpio_mask)
>>         ath9k_hw_gpio_cfg_wmac(...);
>>   else if (AR_SREV_SOC(ah))
>>         ath9k_hw_gpio_cfg_soc(ah, gpio, out, label);
>> 
>> Where ath9k_hw_gpio_cfg_soc() will attempt to issue
>> gpio_request_one() passing the local GPIO number of the controller
>> (0..31) to gpio_request_one().
>> 
>> This is somewhat peculiar and possibly even dangerous: there is
>> nowadays no guarantee of the numbering of these system-wide
>> GPIOs, and assuming that GPIO 0..31 as used by ath9k would
>> correspond to GPIOs 0..31 on the system as a whole seems a bit
>> wild.
>> 
>> My best guess is that everyone actually using this driver has
>> support for the local (custom) GPIO API and the bit in
>> h->caps.gpio_mask is always set for any GPIO the driver may
>> try to obtain, so this facility to use system-wide GPIOs is
>> actually unused and could be deleted.
>> 
>> Anyway: I cannot know if this is really the case, so implement
>> a fallback handling using GPIO descriptors obtained from the
>> ah->dev device indexed 0..31. These can for example be passed
>> in the device tree, ACPI or through board files. I doubt that
>> anyone will use them, but this makes it possible to obtain a
>> system-wide GPIO for any of the 0..31 GPIOs potentially
>> requested by the driver.
>
> ...
>
>> +	/* Obtains a system specific GPIO descriptor from another GPIO controller */
>> +	gpiod = devm_gpiod_get_index(ah->dev, NULL, gpio, flags);
>
>> +
>
> Unnecessary blank line, please don't add it.

I can fix that in the pending branch, no need to resend because of this.

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