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Subject[PATCH v4 22/23] mtd: nand: denali: use non-managed kmalloc() for DMA buffer
Date
As Russell and Lars stated in the discussion [1], using
devm_k*alloc() with DMA is not a good idea.

Let's use kmalloc (not kzalloc because no need for zero-out).
Also, allocate the buffer as late as possible because it must be
freed for any error that follows.

[1] https://lkml.org/lkml/2017/3/8/693

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Russell King <rmk+kernel@armlinux.org.uk>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Robin Murphy <robin.murphy@arm.com>
---

Changes in v4: None
Changes in v3: None
Changes in v2:
- Newly added

drivers/mtd/nand/denali.c | 26 +++++++++++++++++---------
1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/drivers/mtd/nand/denali.c b/drivers/mtd/nand/denali.c
index e4ab397..f2b1592 100644
--- a/drivers/mtd/nand/denali.c
+++ b/drivers/mtd/nand/denali.c
@@ -23,6 +23,7 @@
#include <linux/mutex.h>
#include <linux/mtd/mtd.h>
#include <linux/module.h>
+#include <linux/slab.h>

#include "denali.h"

@@ -1402,13 +1403,6 @@ int denali_init(struct denali_nand_info *denali)
if (ret)
goto disable_irq;

- denali->buf = devm_kzalloc(denali->dev, mtd->writesize + mtd->oobsize,
- GFP_KERNEL);
- if (!denali->buf) {
- ret = -ENOMEM;
- goto disable_irq;
- }
-
if (ioread32(denali->flash_reg + FEATURES) & FEATURES__DMA)
denali->dma_avail = 1;

@@ -1492,17 +1486,30 @@ int denali_init(struct denali_nand_info *denali)
if (ret)
goto disable_irq;

+ /*
+ * This buffer is DMA-mapped by denali_{read,write}_page_raw. Do not
+ * use devm_kmalloc() because the memory allocated by devm_ does not
+ * guarantee DMA-safe alignment.
+ */
+ denali->buf = kmalloc(mtd->writesize + mtd->oobsize, GFP_KERNEL);
+ if (!denali->buf) {
+ ret = -ENOMEM;
+ goto disable_irq;
+ }
+
ret = nand_scan_tail(mtd);
if (ret)
- goto disable_irq;
+ goto free_buf;

ret = mtd_device_register(mtd, NULL, 0);
if (ret) {
dev_err(denali->dev, "Failed to register MTD: %d\n", ret);
- goto disable_irq;
+ goto free_buf;
}
return 0;

+free_buf:
+ kfree(denali->buf);
disable_irq:
denali_disable_irq(denali);

@@ -1516,6 +1523,7 @@ void denali_remove(struct denali_nand_info *denali)
struct mtd_info *mtd = nand_to_mtd(&denali->nand);

nand_release(mtd);
+ kfree(denali->buf);
denali_disable_irq(denali);
}
EXPORT_SYMBOL(denali_remove);
--
2.7.4
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