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

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Date:   Thu, 19 Nov 2020 16:24:10 +0000
From:   Viorel Suman <viorel.suman@....com>
To:     Peter Ujfalusi <peter.ujfalusi@...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 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.

> > -	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.

Viorel