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

Frank Li
2025-10-31T18:35:15Z

On Wed, Oct 29, 2025 at 10:51:17PM +0200, Laurentiu Mihalcea wrote:
>
> On 10/29/2025 6:37 PM, Frank Li wrote:
> > On Wed, Oct 29, 2025 at 06:52:26AM -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.
> > Can you simpifly commit message? The key points are 1: lock, 2: nice API.
> > like regmap_update_bits().
> >
> > Switch to using the regmap API to simplify register access. The regmap
> > infrastructure provides synchronized register access and richer helpers
> > such as regmap_update_bits().
>
>
> this change isn't about simplifying the register access, nor is it about synchronizing
>
> the register access. Previous version was already doing that.
>
>
> the key takeaway here is we want to have the SAME lock used across different APIs.
>
> regmap is a way to do that.

This sentense already be enough descript current situation, you write 6 big
paragaph.

Frank

>
>
> >
> >> 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;
> >> + struct regmap *regmap;
> >> };
> >>
> >> static struct imx8mp_audiomix_reset *to_imx8mp_audiomix_reset(struct reset_controller_dev *rcdev)
> >> @@ -55,26 +56,15 @@ 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 = ffs(mask) - 1;
> >> + 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 +84,50 @@ 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);
> > Not sure why need map parent devices's ioresource here. You'd better use
> > regmap_attach_dev() at parent devices, so dev_get_regmap() will get it.
>
>
> why would we want to force the parent device to use regmap if it doesn't need to?
>
>
> >
> > Frank
> >
> >> + 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 +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() */
> >> 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 +171,6 @@ 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,
> >> .id_table = imx8mp_audiomix_reset_ids,
> >> };
> >>
> >> --
> >> 2.43.0
> >>