diff mbox series

[v2,01/19] mfd: syscon: Add reference counting and device managed support

Message ID 20240527161450.326615-2-herve.codina@bootlin.com (mailing list archive)
State Not Applicable
Headers show
Series Add support for the LAN966x PCI device using a DT overlay | expand

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Context Check Description
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netdev/tree_selection success Guessed tree name to be net-next
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 1169 this patch: 1169
netdev/build_tools success Errors and warnings before: 0 this patch: 0
netdev/cc_maintainers success CCed 2 of 2 maintainers
netdev/build_clang success Errors and warnings before: 917 this patch: 917
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 1183 this patch: 1183
netdev/checkpatch warning WARNING: line length of 85 exceeds 80 columns
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0

Commit Message

Herve Codina May 27, 2024, 4:14 p.m. UTC 
From: Clément Léger <clement.leger@bootlin.com>

Syscon releasing is not supported.
Without release function, unbinding a driver that uses syscon whether
explicitly or due to a module removal left the used syscon in a in-use
state.

For instance a syscon_node_to_regmap() call from a consumer retrieve a
syscon regmap instance. Internally, syscon_node_to_regmap() can create
syscon instance and add it to the existing syscon list. No API is
available to release this syscon instance, remove it from the list and
free it when it is not used anymore.

Introduce reference counting in syscon in order to keep track of syscon
usage using syscon_{get,put}() and add a device managed version of
syscon_regmap_lookup_by_phandle(), to automatically release the syscon
instance on the consumer removal.

Signed-off-by: Clément Léger <clement.leger@bootlin.com>
Signed-off-by: Herve Codina <herve.codina@bootlin.com>
---
 drivers/mfd/syscon.c       | 145 ++++++++++++++++++++++++++++++++++---
 include/linux/mfd/syscon.h |  18 +++++
 2 files changed, 154 insertions(+), 9 deletions(-)

Comments

Arnd Bergmann June 18, 2024, 2:53 p.m. UTC | #1 
On Mon, May 27, 2024, at 18:14, Herve Codina wrote:
> From: Clément Léger <clement.leger@bootlin.com>
>
> Syscon releasing is not supported.
> Without release function, unbinding a driver that uses syscon whether
> explicitly or due to a module removal left the used syscon in a in-use
> state.
>
> For instance a syscon_node_to_regmap() call from a consumer retrieve a
> syscon regmap instance. Internally, syscon_node_to_regmap() can create
> syscon instance and add it to the existing syscon list. No API is
> available to release this syscon instance, remove it from the list and
> free it when it is not used anymore.
>
> Introduce reference counting in syscon in order to keep track of syscon
> usage using syscon_{get,put}() and add a device managed version of
> syscon_regmap_lookup_by_phandle(), to automatically release the syscon
> instance on the consumer removal.
>
> Signed-off-by: Clément Léger <clement.leger@bootlin.com>
> Signed-off-by: Herve Codina <herve.codina@bootlin.com>

This all looks correct from an implementation perspective,
but it does add a lot of complexity if now every syscon user
feels compelled to actually free up their resources again,
while nothing else should actually depend on this.

The only reference I found in your series here is the
reset controller, and it only does a single update to
the regmap in the probe function.

Would it be possible to just make the syscon support in
the reset driver optional and instead poke the register
in the mfd driver itself when this is used as a pci device?
Or do you expect to see the syscon get used in other
places in the future for the PCI case?

      Arnd
Herve Codina June 18, 2024, 3:55 p.m. UTC | #2 
Hi Arnd,

On Tue, 18 Jun 2024 16:53:30 +0200
"Arnd Bergmann" <arnd@arndb.de> wrote:

> On Mon, May 27, 2024, at 18:14, Herve Codina wrote:
> > From: Clément Léger <clement.leger@bootlin.com>
> >
> > Syscon releasing is not supported.
> > Without release function, unbinding a driver that uses syscon whether
> > explicitly or due to a module removal left the used syscon in a in-use
> > state.
> >
> > For instance a syscon_node_to_regmap() call from a consumer retrieve a
> > syscon regmap instance. Internally, syscon_node_to_regmap() can create
> > syscon instance and add it to the existing syscon list. No API is
> > available to release this syscon instance, remove it from the list and
> > free it when it is not used anymore.
> >
> > Introduce reference counting in syscon in order to keep track of syscon
> > usage using syscon_{get,put}() and add a device managed version of
> > syscon_regmap_lookup_by_phandle(), to automatically release the syscon
> > instance on the consumer removal.
> >
> > Signed-off-by: Clément Léger <clement.leger@bootlin.com>
> > Signed-off-by: Herve Codina <herve.codina@bootlin.com>  
> 
> This all looks correct from an implementation perspective,
> but it does add a lot of complexity if now every syscon user
> feels compelled to actually free up their resources again,
> while nothing else should actually depend on this.
> 
> The only reference I found in your series here is the
> reset controller, and it only does a single update to
> the regmap in the probe function.
> 
> Would it be possible to just make the syscon support in
> the reset driver optional and instead poke the register
> in the mfd driver itself when this is used as a pci device?
> Or do you expect to see the syscon get used in other
> places in the future for the PCI case?
> 

IMHO, I don't think that poking the register in the mfd driver and so
avoiding syscon usage is the right solution.

Indeed, additional devices can be added in the DT overlay and an other
syscon user can be present.

Also, overlays can be used on other PCI devices in the future and these PCI
devices can use drivers that are syscon users. In that case, the same kind
of workaround will be needed and maybe a quite more complex one depending on
syscon users.

The root issue is that syscon does not support removal.
I prefer fixing this root issue instead of finding a kind of workaround.

Even if all syscon users are not fixed right now (and probably don't need to
be fixed), a solution with the new devm_syscon_regmap_lookup_by_phandle() is
available and drivers that need to release their resources because of a
device removal can easily move to devm_syscon_regmap_lookup_by_phandle().

Best regards,
Hervé
diff mbox series

Patch

diff --git a/drivers/mfd/syscon.c b/drivers/mfd/syscon.c
index 7d0e91164cba..86898831b842 100644
--- a/drivers/mfd/syscon.c
+++ b/drivers/mfd/syscon.c
@@ -34,6 +34,7 @@  struct syscon {
 	struct regmap *regmap;
 	struct reset_control *reset;
 	struct list_head list;
+	struct kref refcount;
 };
 
 static const struct regmap_config syscon_regmap_config = {
@@ -147,6 +148,8 @@  static struct syscon *of_syscon_register(struct device_node *np, bool check_res)
 
 	syscon->regmap = regmap;
 	syscon->np = np;
+	of_node_get(syscon->np);
+	kref_init(&syscon->refcount);
 
 	spin_lock(&syscon_list_slock);
 	list_add_tail(&syscon->list, &syscon_list);
@@ -168,7 +171,30 @@  static struct syscon *of_syscon_register(struct device_node *np, bool check_res)
 	return ERR_PTR(ret);
 }
 
-static struct regmap *device_node_get_regmap(struct device_node *np,
+static void syscon_free(struct kref *kref)
+{
+	struct syscon *syscon = container_of(kref, struct syscon, refcount);
+
+	spin_lock(&syscon_list_slock);
+	list_del(&syscon->list);
+	spin_unlock(&syscon_list_slock);
+
+	regmap_exit(syscon->regmap);
+	of_node_put(syscon->np);
+	kfree(syscon);
+}
+
+static void syscon_get(struct syscon *syscon)
+{
+	kref_get(&syscon->refcount);
+}
+
+static void syscon_put(struct syscon *syscon)
+{
+	kref_put(&syscon->refcount, syscon_free);
+}
+
+static struct syscon *device_node_get_syscon(struct device_node *np,
 					     bool check_res)
 {
 	struct syscon *entry, *syscon = NULL;
@@ -183,9 +209,23 @@  static struct regmap *device_node_get_regmap(struct device_node *np,
 
 	spin_unlock(&syscon_list_slock);
 
-	if (!syscon)
+	if (!syscon) {
 		syscon = of_syscon_register(np, check_res);
+		if (IS_ERR(syscon))
+			return ERR_CAST(syscon);
+	} else {
+		syscon_get(syscon);
+	}
+
+	return syscon;
+}
 
+static struct regmap *device_node_get_regmap(struct device_node *np,
+					     bool check_res)
+{
+	struct syscon *syscon;
+
+	syscon = device_node_get_syscon(np, check_res);
 	if (IS_ERR(syscon))
 		return ERR_CAST(syscon);
 
@@ -198,12 +238,23 @@  struct regmap *device_node_to_regmap(struct device_node *np)
 }
 EXPORT_SYMBOL_GPL(device_node_to_regmap);
 
-struct regmap *syscon_node_to_regmap(struct device_node *np)
+static struct syscon *syscon_node_to_syscon(struct device_node *np)
 {
 	if (!of_device_is_compatible(np, "syscon"))
 		return ERR_PTR(-EINVAL);
 
-	return device_node_get_regmap(np, true);
+	return device_node_get_syscon(np, true);
+}
+
+struct regmap *syscon_node_to_regmap(struct device_node *np)
+{
+	struct syscon *syscon;
+
+	syscon = syscon_node_to_syscon(np);
+	if (IS_ERR(syscon))
+		return ERR_CAST(syscon);
+
+	return syscon->regmap;
 }
 EXPORT_SYMBOL_GPL(syscon_node_to_regmap);
 
@@ -223,11 +274,11 @@  struct regmap *syscon_regmap_lookup_by_compatible(const char *s)
 }
 EXPORT_SYMBOL_GPL(syscon_regmap_lookup_by_compatible);
 
-struct regmap *syscon_regmap_lookup_by_phandle(struct device_node *np,
-					const char *property)
+static struct syscon *syscon_lookup_by_phandle(struct device_node *np,
+					       const char *property)
 {
 	struct device_node *syscon_np;
-	struct regmap *regmap;
+	struct syscon *syscon;
 
 	if (property)
 		syscon_np = of_parse_phandle(np, property, 0);
@@ -237,12 +288,24 @@  struct regmap *syscon_regmap_lookup_by_phandle(struct device_node *np,
 	if (!syscon_np)
 		return ERR_PTR(-ENODEV);
 
-	regmap = syscon_node_to_regmap(syscon_np);
+	syscon = syscon_node_to_syscon(syscon_np);
 
 	if (property)
 		of_node_put(syscon_np);
 
-	return regmap;
+	return syscon;
+}
+
+struct regmap *syscon_regmap_lookup_by_phandle(struct device_node *np,
+					       const char *property)
+{
+	struct syscon *syscon;
+
+	syscon = syscon_lookup_by_phandle(np, property);
+	if (IS_ERR(syscon))
+		return ERR_CAST(syscon);
+
+	return syscon->regmap;
 }
 EXPORT_SYMBOL_GPL(syscon_regmap_lookup_by_phandle);
 
@@ -293,6 +356,70 @@  struct regmap *syscon_regmap_lookup_by_phandle_optional(struct device_node *np,
 }
 EXPORT_SYMBOL_GPL(syscon_regmap_lookup_by_phandle_optional);
 
+static struct syscon *syscon_from_regmap(struct regmap *regmap)
+{
+	struct syscon *entry, *syscon = NULL;
+
+	spin_lock(&syscon_list_slock);
+
+	list_for_each_entry(entry, &syscon_list, list)
+		if (entry->regmap == regmap) {
+			syscon = entry;
+			break;
+		}
+
+	spin_unlock(&syscon_list_slock);
+
+	return syscon;
+}
+
+void syscon_put_regmap(struct regmap *regmap)
+{
+	struct syscon *syscon;
+
+	syscon = syscon_from_regmap(regmap);
+	if (!syscon)
+		return;
+
+	syscon_put(syscon);
+}
+EXPORT_SYMBOL_GPL(syscon_put_regmap);
+
+static void devm_syscon_release(struct device *dev, void *res)
+{
+	syscon_put(*(struct syscon **)res);
+}
+
+static struct regmap *__devm_syscon_get(struct device *dev,
+					struct syscon *syscon)
+{
+	struct syscon **ptr;
+
+	if (IS_ERR(syscon))
+		return ERR_CAST(syscon);
+
+	ptr = devres_alloc(devm_syscon_release, sizeof(struct syscon *), GFP_KERNEL);
+	if (!ptr) {
+		syscon_put(syscon);
+		return ERR_PTR(-ENOMEM);
+	}
+
+	*ptr = syscon;
+	devres_add(dev, ptr);
+
+	return syscon->regmap;
+}
+
+struct regmap *devm_syscon_regmap_lookup_by_phandle(struct device *dev,
+						    struct device_node *np,
+						    const char *property)
+{
+	struct syscon *syscon = syscon_lookup_by_phandle(np, property);
+
+	return __devm_syscon_get(dev, syscon);
+}
+EXPORT_SYMBOL_GPL(devm_syscon_regmap_lookup_by_phandle);
+
 static int syscon_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
diff --git a/include/linux/mfd/syscon.h b/include/linux/mfd/syscon.h
index c315903f6dab..f742d865a37a 100644
--- a/include/linux/mfd/syscon.h
+++ b/include/linux/mfd/syscon.h
@@ -15,6 +15,7 @@ 
 #include <linux/errno.h>
 
 struct device_node;
+struct device;
 
 #ifdef CONFIG_MFD_SYSCON
 struct regmap *device_node_to_regmap(struct device_node *np);
@@ -28,6 +29,11 @@  struct regmap *syscon_regmap_lookup_by_phandle_args(struct device_node *np,
 						    unsigned int *out_args);
 struct regmap *syscon_regmap_lookup_by_phandle_optional(struct device_node *np,
 							const char *property);
+void syscon_put_regmap(struct regmap *regmap);
+
+struct regmap *devm_syscon_regmap_lookup_by_phandle(struct device *dev,
+						    struct device_node *np,
+						    const char *property);
 #else
 static inline struct regmap *device_node_to_regmap(struct device_node *np)
 {
@@ -67,6 +73,18 @@  static inline struct regmap *syscon_regmap_lookup_by_phandle_optional(
 	return NULL;
 }
 
+static inline void syscon_put_regmap(struct regmap *regmap)
+{
+}
+
+static inline
+struct regmap *devm_syscon_regmap_lookup_by_phandle(struct device *dev,
+						    struct device_node *np,
+						    const char *property)
+{
+	return NULL;
+}
+
 #endif
 
 #endif /* __LINUX_MFD_SYSCON_H__ */