linux-kernel - Re: [RFC PATCH] ASoC: ak4458: use reset control instead of reset gpio

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Message-ID: <c6e7ff22-f421-d05e-621f-738740b30482@ti.com>
Date:   Fri, 20 Nov 2020 15:40:24 +0200
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Viorel Suman <viorel.suman@....com>,
        "Viorel Suman (OSS)" <viorel.suman@....nxp.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        "S.j. Wang" <shengjiu.wang@....com>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Lee Jones <lee.jones@...aro.org>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] ASoC: ak4458: use reset control instead of reset gpio


Hi Viorel,

On 19/11/2020 18.24, Viorel Suman wrote:
> Hi Peter,
> 
>> DTS is supposed to look as follows:
>>>
>>> / {
>>>     ak4458_reset: gpio-reset {
>>>        compatible = "gpio-reset";
>>>        reset-gpios = <&pca6416 4 GPIO_ACTIVE_LOW>;
>>>        #reset-cells = <0>;
>>>        initially-in-reset;
>>
>> I can not find anything resembling to this in next-20201119.
>> Where is the implementation and documentation for this gpio-reset?
> 
> The board schematics is not publicly available; some info may be seen in DTS files below:
> https://source.codeaurora.org/external/imx/linux-imx/tree/arch/arm64/boot/dts/freescale/imx8mm-evk.dts?h=imx_5.4.24_2.1.0
> https://source.codeaurora.org/external/imx/linux-imx/tree/arch/arm64/boot/dts/freescale/imx8mm-ab2.dts?h=imx_5.4.24_2.1.0
> https://source.codeaurora.org/external/imx/linux-imx/tree/arch/arm64/boot/dts/freescale/imx8mp-ab2.dts?h=imx_5.4.24_2.1.0
> 
> In examples above the GPIO is handled by machine driver - wrong approach given that
> it requires machine driver being probed before codec driver.

Right, so this gpio-reset driver is not in mainline. You are adding
support for something which does not exists ;)

> 
>>> -	ak4458->reset_gpiod = devm_gpiod_get_optional(ak4458->dev,
>> "reset",
>>> -						      GPIOD_OUT_LOW);
>>> -	if (IS_ERR(ak4458->reset_gpiod))
>>> -		return PTR_ERR(ak4458->reset_gpiod);
>>> +	ak4458->reset = devm_reset_control_get_optional_shared(ak4458-
>>> dev, NULL);
>>> +	if (IS_ERR(ak4458->reset))
>>> +		return PTR_ERR(ak4458->reset);
>>
>> The binding documentation must be updated and you must support the gpio
>> way as well.
> 
> Sure, make sense.
> 
>> When I had this discussion around using the reset framework for shared
>> enable and/or reset pins it was suggested that _if_ such a driver makes
>> sense then it should internally handle (by using magic strings) the fallback
>> and work with pre-reset binding.
> 
> Thanks, would appreciate if you point me to the discussion you had.

There were few iterations of it when I finally given up, I can quickly
find rfc v2:
https://lkml.org/lkml/2019/10/30/311

Probably in earlier or later series the reset framework was also discussed.

I ended up using GPIOD_FLAGS_BIT_NONEXCLUSIVE in the pcm3168a driver.
https://lkml.org/lkml/2019/11/13/411
- Péter

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