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Subject[PATCH 17/19] mfd-core: 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>
---
drivers/mfd/mfd-core.c | 51 ++++++++++++++++++++++++++++++++++++++++++---
include/linux/mfd/core.h | 14 +++++++++++-
2 files changed, 60 insertions(+), 5 deletions(-)

diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c
index d8b9e35..90e9483 100644
--- a/drivers/mfd/mfd-core.c
+++ b/drivers/mfd/mfd-core.c
@@ -18,6 +18,30 @@
#include <linux/pm_runtime.h>
#include <linux/slab.h>

+int mfd_shared_cell_enable(struct platform_device *pdev)
+{
+ const struct mfd_cell *cell = mfd_get_cell(pdev);
+
+ /* only call enable if the cell hasn't already been enabled */
+ if (atomic_inc_return(cell->usage_count) > 1)
+ return 0;
+
+ return cell->enable(pdev);
+}
+EXPORT_SYMBOL(mfd_shared_cell_enable);
+
+int mfd_shared_cell_disable(struct platform_device *pdev)
+{
+ const struct mfd_cell *cell = mfd_get_cell(pdev);
+
+ /* only disable if no other clients are using it */
+ if (atomic_dec_return(cell->usage_count) != 0)
+ return 0;
+
+ return cell->disable(pdev);
+}
+EXPORT_SYMBOL(mfd_shared_cell_disable);
+
static int mfd_add_device(struct device *parent, int id,
const struct mfd_cell *cell,
struct resource *mem_base,
@@ -97,14 +121,22 @@ fail_alloc:
}

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)
{
int i;
int ret = 0;
+ atomic_t *cnts;
+
+ /* initialize reference counting for all cells */
+ cnts = kcalloc(sizeof(*cnts), n_devs, GFP_KERNEL);
+ if (!cnts)
+ return -ENOMEM;

for (i = 0; i < n_devs; i++) {
+ atomic_set(&cnts[i], 0);
+ cells[i].usage_count = &cnts[i];
ret = mfd_add_device(parent, id, cells + i, mem_base, irq_base);
if (ret)
break;
@@ -117,15 +149,26 @@ int mfd_add_devices(struct device *parent, int id,
}
EXPORT_SYMBOL(mfd_add_devices);

-static int mfd_remove_devices_fn(struct device *dev, void *unused)
+static int mfd_remove_devices_fn(struct device *dev, void *c)
{
- platform_device_unregister(to_platform_device(dev));
+ struct platform_device *pdev = to_platform_device(dev);
+ const struct mfd_cell *cell = mfd_get_cell(pdev);
+ atomic_t **usage_count = c;
+
+ /* find the lowest address of usage_count pointers (for freeing) */
+ if (!*usage_count || (cell->usage_count < *usage_count))
+ *usage_count = cell->usage_count;
+
+ platform_device_unregister(pdev);
return 0;
}

void mfd_remove_devices(struct device *parent)
{
- device_for_each_child(parent, NULL, mfd_remove_devices_fn);
+ atomic_t *cnts = NULL;
+
+ device_for_each_child(parent, &cnts, mfd_remove_devices_fn);
+ kfree(cnts);
}
EXPORT_SYMBOL(mfd_remove_devices);

diff --git a/include/linux/mfd/core.h b/include/linux/mfd/core.h
index c74089e..d13b992 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.
*/
@@ -60,7 +72,7 @@ static inline const struct mfd_cell *mfd_get_cell(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);

--
1.7.2.3


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