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lib: devres: add a comment about the devm_of_iomap() function

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We recently introduced a bug when we tried to convert of_iomap() to
devm_of_iomap().  The problem was that there were two drivers mapping
the same io region.  The first driver was using of_iomap() and the
second driver was using devm_of_iomap() and the kernel booted fine.
When we converted the first drive to use devm_of_iomap() then the second
driver failed with -EBUSY and the kernel couldn't boot.

Let's add a comment to prevent this sort of mistake in the future.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20200609104642.GA43074@mwanda
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Dan Carpenter 2020-06-09 13:46:42 +03:00 committed by Greg Kroah-Hartman
parent 35bd8c07db
commit 7ae731a844
1 changed files with 6 additions and 0 deletions
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6
lib/devres.c
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@ -213,6 +213,12 @@ void __iomem *devm_ioremap_resource_wc(struct device *dev,
* base = devm_of_iomap(&pdev->dev, node, 0, NULL);
* if (IS_ERR(base))
* return PTR_ERR(base);
*
* Please Note: This is not a one-to-one replacement for of_iomap() because the
* of_iomap() function does not track whether the region is already mapped. If
* two drivers try to map the same memory, the of_iomap() function will succeed
* but the the devm_of_iomap() function will return -EBUSY.
*
*/
void __iomem *devm_of_iomap(struct device *dev, struct device_node *node, int index,
resource_size_t *size)