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

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

[ Upstream commit 1869023e24c0de73a160a424dac4621cefd628ae ]

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
    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
    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")
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Gabbasov <andrew_gabbasov@mentor.com>
Link: https://lore.kernel.org/r/20210922184830.29147-1-andrew_gabbasov@mentor.com
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>