linux-kernel - Re: [PATCH RFC] wifi: wilc1000: fix reset line assert/deassert polarity

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Date: Tue, 13 Feb 2024 17:58:04 +0100
From: Alexis Lothoré <alexis.lothore@...tlin.com>
To: David Mosberger-Tang <davidm@...uge.net>, linux-wireless@...r.kernel.org
Cc: Ajay Singh <ajay.kathat@...rochip.com>,
 Claudiu Beznea <claudiu.beznea@...on.dev>, Kalle Valo <kvalo@...nel.org>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] wifi: wilc1000: fix reset line assert/deassert
 polarity

On 2/13/24 17:42, David Mosberger-Tang wrote:
> On Tue, 2024-02-13 at 16:22 +0100, Alexis Lothoré wrote:
>> When using a wilc1000 chip over a spi bus, users can optionally define a
>> reset gpio and a chip enable gpio. The reset line of wilc1000 is active
>> low, so to hold the chip in reset, a low (physical) value must be applied.
>>
>> The corresponding device tree binding documentation was introduced by
>> commit f31ee3c0a555 ("wilc1000: Document enable-gpios and reset-gpios
>> properties") and correctly indicates that the reset line is an active-low
>> signal. However, the corresponding driver part, brought by commit
>> ec031ac4792c ("wilc1000: Add reset/enable GPIO support to SPI driver"), is
>> misusing the gpiod APIs and apply an inverted logic when powering up/down
>> the chip (for example, setting the reset line to a logic "1" during power
>> up, which in fact asserts the reset line when device tree describes the
>> reset line as GPIO_ACTIVE_LOW).
> 
> Note that commit ec031ac4792c is doing the right thing in regards to an
> ACTIVE_LOW RESET pin and the binding documentation is consistent with that code.
> 
> It was later on that commit fcf690b0 flipped the RESET line polarity to treat it
> as GPIO_ACTIVE_HIGH.  I never understood why that was done and, as you noted, it
> introduced in inconsistency with the binding documentation.

Ah, you are right, and I was wrong citing your GPIOs patch as faulty
(git-blaming too fast !), thanks for the clarification. I missed this patch from
Ajay (fcf690b0) flipping the reset logic. Maybe he had issues while missing
proper device tree configuration and then submitted this flip ?

> On our platform, we never merged commit fcf690b0 and hence our DTS already
> defines the RESET pin as GPIO_ACTIVE_LOW.  So, I don't have any issues at all
> with your patch! :-)

So in the end, the patch should be about a mere revert. I will update
accordingly when relevant, but before that I'll wait for some feedback about the
potential issue of this patch (forcing users to udpate faulty devicetree)

Thanks,
Alexis

-- 
Alexis Lothoré, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com