mtd: nand: denali: use non-managed kmalloc() for DMA buffer

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>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>

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"
 
@@ -1352,13 +1353,6 @@ 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;
 
@@ -1443,17 +1437,30 @@ 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);
 
@@ -1467,6 +1474,7 @@ 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);