[PATCH] memory: renesas-rpc-if: Avoid unaligned bus access for HyperFlash

Andrew Gabbasov
2021-09-22T18:48:55Z

HyperFlash devices in Renesas SoCs use 2-bytes addressing, according
to HW manual paragraph 62.3.3 (which officially describes Serial Flash
access, but seems to be applicable to HyperFlash too). And 1-byte bus
read operations to 2-bytes unaligned addresses in external address space
read mode work incorrectly (returns the other byte from the same word).

Function memcpy_fromio(), used by the driver to read data from the bus,
in ARM64 architecture (to which Renesas cores belong) uses 8-bytes
bus accesses for appropriate aligned addresses, and 1-bytes accesses
for other addresses. This results in incorrect data read from HyperFlash
in unaligned cases.

This issue can be reproduced using something like the following commands
(where mtd1 is a parition on Hyperflash storage, defined properly
in a device tree):

[Correct fragment, read from Hyperflash]

root@rcar-gen3:~# dd if=/dev/mtd1 of=/tmp/zz bs=32 count=1
1+0 records in
1+0 records out
root@rcar-gen3:~# hexdump -C /tmp/zz
00000000 f4 03 00 aa f5 03 01 aa f6 03 02 aa f7 03 03 aa |................|
00000010 00 00 80 d2 40 20 18 d5 00 06 81 d2 a0 18 a6 f2 |....@ ..........|
00000020

[Incorrect read of the same fragment: see the difference at offsets 8-11]

root@rcar-gen3:~# dd if=/dev/mtd1 of=/tmp/zz bs=12 count=1
1+0 records in
1+0 records out
root@rcar-gen3:~# hexdump -C /tmp/zz
00000000 f4 03 00 aa f5 03 01 aa 03 03 aa aa |............|
0000000c

Fix this issue by creating a local replacement of the copying function,
that performs only properly aligned bus accesses, and is used for reading
from HyperFlash.

Fixes: ca7d8b980b67f ("memory: add Renesas RPC-IF driver")
Signed-off-by: Andrew Gabbasov <andrew_gabbasov@mentor.com>
---
drivers/memory/renesas-rpc-if.c | 47 ++++++++++++++++++++++++++++++++-
1 file changed, 46 insertions(+), 1 deletion(-)

diff --git a/drivers/memory/renesas-rpc-if.c b/drivers/memory/renesas-rpc-if.c
index 45eed659b0c6..374c92e57538 100644
--- a/drivers/memory/renesas-rpc-if.c
+++ b/drivers/memory/renesas-rpc-if.c
@@ -502,6 +502,48 @@ int rpcif_manual_xfer(struct rpcif *rpc)
}
EXPORT_SYMBOL(rpcif_manual_xfer);

+static void memcpy_fromio_readw(void *to,
+ const void __iomem *from,
+ size_t count)
+{
+ const int maxw = (IS_ENABLED(CONFIG_64BIT)) ? 8 : 4;
+ u8 buf[2];
+
+ if (count && ((unsigned long)from & 1)) {
+ *(u16 *)buf = __raw_readw((void __iomem *)((unsigned long)from & ~1));
+ *(u8 *)to = buf[1];
+ from++;
+ to++;
+ count--;
+ }
+ while (count >= 2 && !IS_ALIGNED((unsigned long)from, maxw)) {
+ *(u16 *)to = __raw_readw(from);
+ from += 2;
+ to += 2;
+ count -= 2;
+ }
+ while (count >= maxw) {
+#ifdef CONFIG_64BIT
+ *(u64 *)to = __raw_readq(from);
+#else
+ *(u32 *)to = __raw_readl(from);
+#endif
+ from += maxw;
+ to += maxw;
+ count -= maxw;
+ }
+ while (count >= 2) {
+ *(u16 *)to = __raw_readw(from);
+ from += 2;
+ to += 2;
+ count -= 2;
+ }
+ if (count) {
+ *(u16 *)buf = __raw_readw(from);
+ *(u8 *)to = buf[0];
+ }
+}
+
ssize_t rpcif_dirmap_read(struct rpcif *rpc, u64 offs, size_t len, void *buf)
{
loff_t from = offs & (RPCIF_DIRMAP_SIZE - 1);
@@ -523,7 +565,10 @@ ssize_t rpcif_dirmap_read(struct rpcif *rpc, u64 offs, size_t len, void *buf)
regmap_write(rpc->regmap, RPCIF_DRDMCR, rpc->dummy);
regmap_write(rpc->regmap, RPCIF_DRDRENR, rpc->ddr);

- memcpy_fromio(buf, rpc->dirmap + from, len);
+ if (rpc->bus_size == 2)
+ memcpy_fromio_readw(buf, rpc->dirmap + from, len);
+ else
+ memcpy_fromio(buf, rpc->dirmap + from, len);

pm_runtime_put(rpc->dev);

--
2.21.0