[PATCH v3] mtd: fix oops when writing to phram device on arm64

[Huaijie Yi <yihuaijie@xxxxxxxxxx>]

From: yihuaijie <yihuaijie@xxxxxxxxxx>

memcpy() to memory remaped by ioremap() at an address not aligned
to 8-bytes will cause oops on arm64 platform, fixing this by using
ioremap_wc().

e.g.
writing through jffs2 on a phram device cause following error:

Unable to handle kernel paging request at virtual address ffffff800f93700c
pgd = ffffffc00385c000
[ffffff800f93700c] *pgd=0000000000000000, *pud=0000000000000000
Internal error: Oops: 96000061 [#1] PREEMPT SMP
task: ffffffc003549b10 task.stack: ffffffc0b8bc8000
PC is at __memcpy+0xc0/0x180
LR is at phram_write+0x5c/0x78 [phram]
pc : [<ffffff8008484740>] lr : [<ffffff8000d731a4>] pstate: 80000005
sp : ffffffc0b8bcb8c0
x29: ffffffc0b8bcb8c0 x28: 000000000093700c
x27: 0000000000000001 x26: 0000000000000000
x25: 0000000000000001 x24: 0000000000000000
x23: ffffffc5b6db8480 x22: ffffffc0b8bcb990
x21: ffffff800f000000 x20: 000000000093700c
x19: 0000000000000044 x18: 000000000000000a
x17: 0000000000000c00 x16: 0000000000000400
x15: 000000000001e125 x14: 34347830203a6e65
x13: 6c202c6330303733 x12: 397830203a726464
x11: 61202c3030303030 x10: 3066303038666666
x9 : 6666667830203a56 x8 : 0000000298f7fb1d
x7 : 00000044e0021985 x6 : ffffff800f93700c
x5 : 0000000000000000 x4 : 0000000000000000
x3 : ffffff8008cbe018 x2 : ffffffffffffffc4
x1 : ffffffc5b6db8490 x0 : ffffff800f93700c

Signed-off-by: Huaijie Yi <yihuaijie@xxxxxxxxxx>
---
v1->v3
let user to choose using ioremap() or ioremap_wc() through module param

 drivers/mtd/devices/phram.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/drivers/mtd/devices/phram.c b/drivers/mtd/devices/phram.c
index c467286..a5833dd 100644
--- a/drivers/mtd/devices/phram.c
+++ b/drivers/mtd/devices/phram.c
@@ -27,6 +27,20 @@
 #include <linux/slab.h>
 #include <linux/mtd/mtd.h>
 
+/*
+ * It is of the form:
+ * wc=Y/N for module case
+ * phram.wc=Y/N for built-in case
+ */
+static bool wc;
+module_param(wc, bool, 0);
+MODULE_PARM_DESC(wc, "How we remap reserved memory to a phram device\n"
+		"\tSay N(default) to use ioremap(): \"wc=N\"\n"
+		"\tSay Y to use ioremap_wc(): \"wc=Y\"\n"
+		"\tOn ARM64, writing to phram device using ioremap()\n"
+		"\tat addr not aligned to 8-bytes will cause oops,\n"
+		"\tioremap_wc() could fix it.");
+
 struct phram_mtd_list {
 	struct mtd_info mtd;
 	struct list_head list;
@@ -98,7 +112,11 @@ static int register_device(char *name, phys_addr_t start, size_t len)
 		goto out0;
 
 	ret = -EIO;
-	new->mtd.priv = ioremap(start, len);
+	if (wc)
+		new->mtd.priv = ioremap_wc(start, len);
+	else
+		new->mtd.priv = ioremap(start, len);
+
 	if (!new->mtd.priv) {
 		pr_err("ioremap failed\n");
 		goto out1;
-- 
1.8.5.6



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