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

From: Laurentiu Mihalcea <redacted>

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 <redacted>
---
 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;

+	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() */