linux-kernel - Re: [PATCH v3 5/8] reset: imx8mp-audiomix: Switch to using regmap API

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Message-ID: <105ed81ed67d8e4cacb63a83a606e206a4d6f310.camel@pengutronix.de>
Date: Thu, 30 Oct 2025 14:06:29 +0100
From: Philipp Zabel <p.zabel@...gutronix.de>
To: Laurentiu Mihalcea <laurentiumihalcea111@...il.com>, Abel Vesa
	 <abelvesa@...nel.org>, Peng Fan <peng.fan@....com>, Michael Turquette
	 <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>, Rob Herring
	 <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
	 <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>, Fabio Estevam
	 <festevam@...il.com>, Daniel Baluta <daniel.baluta@....com>, Shengjiu Wang
	 <shengjiu.wang@....com>
Cc: linux-clk@...r.kernel.org, imx@...ts.linux.dev,
 devicetree@...r.kernel.org, 	linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org,  Pengutronix Kernel Team	
 <kernel@...gutronix.de>
Subject: Re: [PATCH v3 5/8] reset: imx8mp-audiomix: Switch to using regmap
 API

On Mi, 2025-10-29 at 06:52 -0700, Laurentiu Mihalcea wrote:
> From: Laurentiu Mihalcea <laurentiu.mihalcea@....com>
> 
> As far as the Linux kernel is concerned, block devices such as i.MX8MP's
> AUDIOMIX block control or i.MX8ULP's SIM LPAV can simultaneously act as
> clock controllers, reset controllers or mux controllers. Since these IPs
> offer different functionalities through different subsystem APIs, it's
> important to make sure that the register R-M-W cycles are performed under
> the same lock across all subsystem APIs. This will ensure that registers
> will not end up with the wrong values because of race conditions (e.g.
> clock consumer tries to update block control register A, while, at the
> same time, reset consumer tries to update the same block control register).
> 
> However, the aforementioned race conditions will only impact block control
> IPs which use the same register for multiple functionalities. For example,
> i.MX8MP's AUDIOMIX block control IP provides clock gating functionalities
> and reset control functionalities through different registers. This is why
> the current approach (i.e. clock control and reset control work using
> different locks) has worked well so far.
> 
> Since we want to extend this driver to be usable for i.MX8ULP's SIM LPAV
> block control IP, we need to make sure that clock control, reset control,
> and mux control APIs use the same lock since all of these functionalities
> are performed using the SYSCTRL0 register.
> 
> To do so, we need to switch to the regmap API and, if possible, use the
> parent device's regmap, which, in the case of i.MX8ULP, will be the clock
> controller. This way, we can make sure that the clock gates and the reset
> controller will use the same lock to perform the register R-M-W cycles.
> 
> This change will also work fine for cases where we don't really need to
> share the lock across multiple APIs (e.g. i.MX8MP's AUDIOMIX block
> control) since regmap will take care of the locking we were previously
> explicitly performing in the driver.
> 
> The transition to the regmap API also involves some cleanup. Specifically,
> we can make use of devres to unmap the device's memory and get rid of the
> memory mapping-related error paths and the remove() function altogether.
> 
> Signed-off-by: Laurentiu Mihalcea <laurentiu.mihalcea@....com>
> ---
>  drivers/reset/reset-imx8mp-audiomix.c | 91 +++++++++++++++++----------
>  1 file changed, 57 insertions(+), 34 deletions(-)
> 
> diff --git a/drivers/reset/reset-imx8mp-audiomix.c b/drivers/reset/reset-imx8mp-audiomix.c
> index e9643365a62c..3f6d11270918 100644
> --- a/drivers/reset/reset-imx8mp-audiomix.c
> +++ b/drivers/reset/reset-imx8mp-audiomix.c
> @@ -11,6 +11,7 @@
>  #include <linux/module.h>
>  #include <linux/of.h>
>  #include <linux/of_address.h>
> +#include <linux/regmap.h>
>  #include <linux/reset-controller.h>
>  
>  #define IMX8MP_AUDIOMIX_EARC_RESET_OFFSET	0x200
> @@ -42,8 +43,8 @@ static const struct imx8mp_reset_map reset_map[] = {
>  
>  struct imx8mp_audiomix_reset {
>  	struct reset_controller_dev rcdev;
> -	spinlock_t lock; /* protect register read-modify-write cycle */
>  	void __iomem *base;

Drop base as well, better let devres handle this.

[...]

> +/* assumption: registered only if not using parent regmap */
> +static void imx8mp_audiomix_reset_iounmap(void *data)

Pass base instead of dev.

> +{
> +	struct imx8mp_audiomix_reset *priv = dev_get_drvdata(data);
> +
> +	iounmap(priv->base);

	void __iomem *base = data;

	iounmap(base);

> +}
> +
> +/* assumption: dev_set_drvdata() is called before this */

Why not just pass priv instead of dev?

> +static int imx8mp_audiomix_reset_get_regmap(struct device *dev)
> +{
> +	struct imx8mp_audiomix_reset *priv;
> +	int ret;
> +
> +	priv = dev_get_drvdata(dev);
> +
> +	/* try to use the parent's regmap */
> +	priv->regmap = dev_get_regmap(dev->parent, NULL);
> +	if (priv->regmap)
> +		return 0;
> +
> +	/* ... if that's not possible then initialize the regmap right now */
> +	priv->base = of_iomap(dev->parent->of_node, 0);

Make base a local variable ...

> +	if (!priv->base)
> +		return dev_err_probe(dev, -ENOMEM, "failed to iomap address space\n");
> +
> +	ret = devm_add_action_or_reset(dev, imx8mp_audiomix_reset_iounmap, dev);

... and pass it as data instead of dev.

> +	if (ret)
> +		return dev_err_probe(dev, ret, "failed to register action\n");
> +
> +	priv->regmap = devm_regmap_init_mmio(dev, priv->base, &regmap_config);
> +	if (IS_ERR(priv->regmap))
> +		return dev_err_probe(dev, PTR_ERR(priv->regmap),
> +				     "failed to initialize regmap\n");
> +
> +	return 0;
> +}
> +
>  static int imx8mp_audiomix_reset_probe(struct auxiliary_device *adev,
>  				       const struct auxiliary_device_id *id)
>  {
> @@ -105,36 +139,26 @@ static int imx8mp_audiomix_reset_probe(struct auxiliary_device *adev,
>  	if (!priv)
>  		return -ENOMEM;
>  
> -	spin_lock_init(&priv->lock);
> -
>  	priv->rcdev.owner     = THIS_MODULE;
>  	priv->rcdev.nr_resets = ARRAY_SIZE(reset_map);
>  	priv->rcdev.ops       = &imx8mp_audiomix_reset_ops;
>  	priv->rcdev.of_node   = dev->parent->of_node;
>  	priv->rcdev.dev	      = dev;
>  	priv->rcdev.of_reset_n_cells = 1;
> -	priv->base            = of_iomap(dev->parent->of_node, 0);
> -	if (!priv->base)
> -		return -ENOMEM;
>  
> +	/* keep before call to imx8mp_audiomix_reset_init_regmap() */

Not needed if priv is passed to it directly.

regards
Philipp