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

Philipp Zabel
2025-10-30T13:06:55Z

On Mi, 2025-10-29 at 06:52 -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 | 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