mfd: Add refcounting support to mfd_cells

This provides convenience functions for sharing of cells across
multiple mfd clients.  Mfd drivers can provide enable/disable hooks
to actually tweak the hardware, and clients can call
mfd_shared_cell_{en,dis}able without having to worry about whether
or not another client happens to have enabled or disabled the
cell/hardware.

Note that this is purely optional; drivers can continue to use
the mfd_cell's enable/disable hooks for their own purposes, if
desired.

Signed-off-by: Andres Salomon <dilinger@queued.net>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

1 files changed, 13 insertions, 1 deletions

diff --git a/include/linux/mfd/core.h b/include/linux/mfd/core.h
index 71cd1f983cce..22a2f5ebd9db 100644
--- a/include/linux/mfd/core.h
+++ b/include/linux/mfd/core.h
@@ -25,8 +25,11 @@ struct mfd_cell {
         const char              *name;
         int                     id;
 
+        /* refcounting for multiple drivers to use a single cell */
+        atomic_t                *usage_count;
         int                     (*enable)(struct platform_device *dev);
         int                     (*disable)(struct platform_device *dev);
+
         int                     (*suspend)(struct platform_device *dev);
         int                     (*resume)(struct platform_device *dev);
 
@@ -51,6 +54,15 @@ struct mfd_cell {
 };
 
 /*
+ * Convenience functions for clients using shared cells.  Refcounting
+ * happens automatically, with the cell's enable/disable callbacks
+ * being called only when a device is first being enabled or no other
+ * clients are making use of it.
+ */
+extern int mfd_shared_cell_enable(struct platform_device *pdev);
+extern int mfd_shared_cell_disable(struct platform_device *pdev);
+
+/*
  * Given a platform device that's been created by mfd_add_devices(), fetch
  * the mfd_cell that created it.
  */
@@ -69,7 +81,7 @@ static inline void *mfd_get_data(struct platform_device *pdev)
 }
 
 extern int mfd_add_devices(struct device *parent, int id,
-                           const struct mfd_cell *cells, int n_devs,
+                           struct mfd_cell *cells, int n_devs,
                            struct resource *mem_base,
                            int irq_base);