Re: [PATCH v2 5/8] reset: imx8mp-audiomix: Switch to using regmap API

[Frank Li <Frank.li@nxp.com>]

On Fri, Oct 17, 2025 at 04:20:22AM -0700, Laurentiu Mihalcea wrote:
> From: Laurentiu Mihalcea <laurentiu.mihalcea@nxp.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@nxp.com>
> ---
>  drivers/reset/reset-imx8mp-audiomix.c | 95 +++++++++++++++++----------
>  1 file changed, 61 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/reset/reset-imx8mp-audiomix.c b/drivers/reset/reset-imx8mp-audiomix.c
> index e9643365a62c..c74ce6e04177 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
> @@ -19,6 +20,7 @@
>  struct imx8mp_reset_map {
>  	unsigned int offset;
>  	unsigned int mask;
> +	unsigned int shift;
>  	bool active_low;
>  };
>
> @@ -26,24 +28,27 @@ static const struct imx8mp_reset_map reset_map[] = {
>  	[IMX8MP_AUDIOMIX_EARC_RESET] = {
>  		.offset	= IMX8MP_AUDIOMIX_EARC_RESET_OFFSET,
>  		.mask = BIT(0),
> +		.shift = 0,
>  		.active_low = true,
>  	},
>  	[IMX8MP_AUDIOMIX_EARC_PHY_RESET] = {
>  		.offset	= IMX8MP_AUDIOMIX_EARC_RESET_OFFSET,
>  		.mask = BIT(1),
> +		.shift = 1,
>  		.active_low = true,
>  	},
>  	[IMX8MP_AUDIOMIX_DSP_RUNSTALL] = {
>  		.offset	= IMX8MP_AUDIOMIX_DSP_RUNSTALL_OFFSET,
>  		.mask = BIT(5),
> +		.shift = 5,

why need shift?  you can use ffs(mask) to get shift.

>  		.active_low = false,
>  	},
>  };
>
>  struct imx8mp_audiomix_reset {
>  	struct reset_controller_dev rcdev;
> -	spinlock_t lock; /* protect register read-modify-write cycle */
>  	void __iomem *base;
> +	struct regmap *regmap;
>  };
>
>  static struct imx8mp_audiomix_reset *to_imx8mp_audiomix_reset(struct reset_controller_dev *rcdev)
> @@ -55,26 +60,15 @@ static int imx8mp_audiomix_update(struct reset_controller_dev *rcdev,
>  				  unsigned long id, bool assert)
>  {
>  	struct imx8mp_audiomix_reset *priv = to_imx8mp_audiomix_reset(rcdev);
> -	void __iomem *reg_addr = priv->base;
> -	unsigned int mask, offset, active_low;
> -	unsigned long reg, flags;
> +	unsigned int mask, offset, active_low, shift, val;
>
>  	mask = reset_map[id].mask;
>  	offset = reset_map[id].offset;
>  	active_low = reset_map[id].active_low;
> +	shift = reset_map[id].shift;
> +	val = (active_low ^ assert) << shift;
>
> -	spin_lock_irqsave(&priv->lock, flags);
> -
> -	reg = readl(reg_addr + offset);
> -	if (active_low ^ assert)
> -		reg |= mask;
> -	else
> -		reg &= ~mask;
> -	writel(reg, reg_addr + offset);
> -
> -	spin_unlock_irqrestore(&priv->lock, flags);
> -
> -	return 0;
> +	return regmap_update_bits(priv->regmap, offset, mask, val);
>  }
>
>  static int imx8mp_audiomix_reset_assert(struct reset_controller_dev *rcdev,
> @@ -94,6 +88,50 @@ static const struct reset_control_ops imx8mp_audiomix_reset_ops = {
>  	.deassert = imx8mp_audiomix_reset_deassert,
>  };
>
> +static const struct regmap_config regmap_config = {
> +	.reg_bits = 32,
> +	.val_bits = 32,
> +	.reg_stride = 4,
> +};
> +
> +/* assumption: registered only if not using parent regmap */
> +static void imx8mp_audiomix_reset_iounmap(void *data)
> +{
> +	struct imx8mp_audiomix_reset *priv = dev_get_drvdata(data);
> +
> +	iounmap(priv->base);
> +}
> +
> +/* assumption: dev_set_drvdata() is called before this */
> +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);
> +	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);
> +	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 +143,26 @@ 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() */
>  	dev_set_drvdata(dev, priv);
>
> +	ret = imx8mp_audiomix_reset_get_regmap(dev);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "failed to get regmap\n");
> +
>  	ret = devm_reset_controller_register(dev, &priv->rcdev);
>  	if (ret)
> -		goto out_unmap;
> +		return dev_err_probe(dev, ret,
> +				     "failed to register reset controller\n");
>
>  	return 0;
> -
> -out_unmap:
> -	iounmap(priv->base);
> -	return ret;
> -}
> -
> -static void imx8mp_audiomix_reset_remove(struct auxiliary_device *adev)
> -{
> -	struct imx8mp_audiomix_reset *priv = dev_get_drvdata(&adev->dev);
> -
> -	iounmap(priv->base);
>  }
>
>  static const struct auxiliary_device_id imx8mp_audiomix_reset_ids[] = {
> @@ -147,7 +175,6 @@ MODULE_DEVICE_TABLE(auxiliary, imx8mp_audiomix_reset_ids);
>
>  static struct auxiliary_driver imx8mp_audiomix_reset_driver = {
>  	.probe		= imx8mp_audiomix_reset_probe,
> -	.remove		= imx8mp_audiomix_reset_remove,

cleanup imx8mp_audiomix_reset_remove need seperate patch.

Frank

>  	.id_table	= imx8mp_audiomix_reset_ids,
>  };
>
> --
> 2.43.0
>