mfd: Stop setting refcounting pointers in original mfd_cell arrays

Commit 1e29af62 ("mfd: Add refcounting
support to mfd_cells") had to drop the "const" keyword on the "cell"
parameter of mfd_add_devices(), as it added the refcounting pointers
to the objects of the passed mfd_cell array itself.

However, the mfd core code operates on copies of the mfd_cell objects,
so there's no need to modify the originally passed objects.

Hence, move the setting of the refcounting pointers from mfd_add_devices()
to mfd_platform_add_cell(), where the copy of the mfd_cell objects is made.
mfd_clone_cell() can just pass (a copy of) the original usage_count
pointer.

This allows to make the "cell" parameter of mfd_add_devices() "const"
again, and avoids future race conditions when registering multiple
instances of the same device in parallel.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/mfd-core.c

@@ -63,7 +63,8 @@ int mfd_cell_disable(struct platform_device *pdev)
 EXPORT_SYMBOL(mfd_cell_disable);
 
 static int mfd_platform_add_cell(struct platform_device *pdev,
-				 const struct mfd_cell *cell)
+				 const struct mfd_cell *cell,
+				 atomic_t *usage_count)
 {
 	if (!cell)
 		return 0;
@@ -72,11 +73,12 @@ static int mfd_platform_add_cell(struct platform_device *pdev,
 	if (!pdev->mfd_cell)
 		return -ENOMEM;
 
+	pdev->mfd_cell->usage_count = usage_count;
 	return 0;
 }
 
 static int mfd_add_device(struct device *parent, int id,
-			  const struct mfd_cell *cell,
+			  const struct mfd_cell *cell, atomic_t *usage_count,
 			  struct resource *mem_base,
 			  int irq_base, struct irq_domain *domain)
 {
@@ -115,7 +117,7 @@ static int mfd_add_device(struct device *parent, int id,
 			goto fail_res;
 	}
 
-	ret = mfd_platform_add_cell(pdev, cell);
+	ret = mfd_platform_add_cell(pdev, cell, usage_count);
 	if (ret)
 		goto fail_res;
 
@@ -180,7 +182,7 @@ static int mfd_add_device(struct device *parent, int id,
 }
 
 int mfd_add_devices(struct device *parent, int id,
-		    struct mfd_cell *cells, int n_devs,
+		    const struct mfd_cell *cells, int n_devs,
 		    struct resource *mem_base,
 		    int irq_base, struct irq_domain *domain)
 {
@@ -195,8 +197,7 @@ int mfd_add_devices(struct device *parent, int id,
 
 	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,
+		ret = mfd_add_device(parent, id, cells + i, cnts + i, mem_base,
 				     irq_base, domain);
 		if (ret)
 			break;
@@ -259,8 +260,8 @@ int mfd_clone_cell(const char *cell, const char **clones, size_t n_clones)
 	for (i = 0; i < n_clones; i++) {
 		cell_entry.name = clones[i];
 		/* don't give up if a single call fails; just report error */
-		if (mfd_add_device(pdev->dev.parent, -1, &cell_entry, NULL, 0,
-				   NULL))
+		if (mfd_add_device(pdev->dev.parent, -1, &cell_entry,
+				   cell_entry.usage_count, NULL, 0, NULL))
 			dev_err(dev, "failed to create platform device '%s'\n",
 					clones[i]);
 	}

include/linux/mfd/core.h

@@ -98,7 +98,7 @@ static inline const struct mfd_cell *mfd_get_cell(struct platform_device *pdev)
 }
 
 extern int mfd_add_devices(struct device *parent, int id,
-			   struct mfd_cell *cells, int n_devs,
+			   const struct mfd_cell *cells, int n_devs,
 			   struct resource *mem_base,
 			   int irq_base, struct irq_domain *irq_domain);