pinctrl: add usecount to pins for muxing

Multiple mapping table entries could reference the same pin, and hence
"own" it. This would be unusual now that pinctrl_get() represents a single
state for a client device, but in the future when it represents all known
states for a device, this is quite likely. Implement reference counting
for pin ownership to handle this.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Dong Aisheng <dong.aisheng@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

2 files changed, 28 insertions, 5 deletions

diff --git a/drivers/pinctrl/core.h b/drivers/pinctrl/core.h
index 5f258b793400..0bc52ecaf710 100644
--- a/drivers/pinctrl/core.h
+++ b/drivers/pinctrl/core.h
@@ -82,7 +82,14 @@ struct pinctrl_setting {
  * @name: a name for the pin, e.g. the name of the pin/pad/finger on a
  *      datasheet or such
  * @dynamic_name: if the name of this pin was dynamically allocated
- * @owner: the device holding this pin or NULL of no device has claimed it
+ * @usecount: If zero, the pin is not claimed, and @owner should be NULL.
+ *      If non-zero, this pin is claimed by @owner. This field is an integer
+ *      rather than a boolean, since pinctrl_get() might process multiple
+ *      mapping table entries that refer to, and hence claim, the same group
+ *      or pin, and each of these will increment the @usecount.
+ * @owner: The name of the entity owning the pin. Typically, this is the name
+ *      of the device that called pinctrl_get(). Alternatively, it may be the
+ *      name of the GPIO passed to pinctrl_request_gpio().
  */
 struct pin_desc {
         struct pinctrl_dev *pctldev;
@@ -90,6 +97,7 @@ struct pin_desc {
         bool dynamic_name;
         /* These fields only added when supporting pinmux drivers */
 #ifdef CONFIG_PINMUX
+        unsigned usecount;
         const char *owner;
 #endif
 };
diff --git a/drivers/pinctrl/pinmux.c b/drivers/pinctrl/pinmux.c
index f0fb98d252e8..56ca42e6a6ec 100644
--- a/drivers/pinctrl/pinmux.c
+++ b/drivers/pinctrl/pinmux.c
@@ -83,11 +83,16 @@ static int pin_request(struct pinctrl_dev *pctldev,
                 goto out;
         }
 
-        if (desc->owner && strcmp(desc->owner, owner)) {
+        if (desc->usecount && strcmp(desc->owner, owner)) {
                 dev_err(pctldev->dev,
                         "pin already requested\n");
                 goto out;
         }
+
+        desc->usecount++;
+        if (desc->usecount > 1)
+                return 0;
+
         desc->owner = owner;
 
         /* Let each pin increase references to this module */
@@ -111,12 +116,18 @@ static int pin_request(struct pinctrl_dev *pctldev,
         else
                 status = 0;
 
-        if (status)
+        if (status) {
                 dev_err(pctldev->dev, "->request on device %s failed for pin %d\n",
                        pctldev->desc->name, pin);
+                module_put(pctldev->owner);
+        }
+
 out_free_pin:
-        if (status)
-                desc->owner = NULL;
+        if (status) {
+                desc->usecount--;
+                if (!desc->usecount)
+                        desc->owner = NULL;
+        }
 out:
         if (status)
                 dev_err(pctldev->dev, "pin-%d (%s) status %d\n",
@@ -150,6 +161,10 @@ static const char *pin_free(struct pinctrl_dev *pctldev, int pin,
                 return NULL;
         }
 
+        desc->usecount--;
+        if (desc->usecount)
+                return NULL;
+
         /*
          * If there is no kind of request function for the pin we just assume
          * we got it by default and proceed.