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

[Andrew Gabbasov <andrew_gabbasov@mentor.com>]

Hello Krzysztof,

> -----Original Message-----
> From: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
> Sent: Friday, September 24, 2021 2:13 PM
> To: Gabbasov, Andrew <Andrew_Gabbasov@mentor.com>; linux-renesas-soc@vger.kernel.org; linux-
> kernel@vger.kernel.org; Sergei Shtylyov <sergei.shtylyov@gmail.com>; Geert Uytterhoeven <geert+renesas@glider.be>
> Subject: Re: [PATCH] memory: renesas-rpc-if: Avoid unaligned bus access for HyperFlash
> 
> On 22/09/2021 20:48, Andrew Gabbasov wrote:
> > 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(-)
> >
> 
> Thanks for the patch.
> 
> Please rebase and test on a recent Linux kernel. This looks like work on
> something slightly older or stable kernel, since you Cc not the address
> from maintainers.

The patch is already against the recent kernel versions.
Sorry for using wrong address, I have probably taken it from some
older mailing lists.

> The patch came slightly after Wolfram's and I wonder whether you hit
> similar issue:
> https://lore.kernel.org/lkml/20210922091007.5516-1-wsa+renesas@sang-engineering.com/

If I correctly understand, the underlying issue looks similar (improperly aligned
memory/register accesses), but the affected areas are different, even non-intersecting:
Wolfram fixes register access, affecting manual mode reads/writes, having problems
with QSPI devices, while my fix is related to external address space reads (mapped
memory access) with Hyperflash devices.

Thanks.

Best regards,
Andrew