L2 cache management and busdma - or, "damnit USB, who you not like me"

[Adrian Chadd]

On 22 December 2015 at 03:26, Bernd Walter <ticso at cicely7.cicely.de> wrote:
> On Tue, Dec 22, 2015 at 12:12:55AM -0800, Adrian Chadd wrote:
>> hi,
>>
>> It shouldn't be - the atheros mips doesn't have l2 cache.
>>
>> I wish I could reproduce your issue. :(
>
> It is strange that you couldn't reproduce the problem.
> For me It happened on so many HW combinations of sticks and magnetic USB drive,
> with different AR9331 boards and also with the WDR-4300.
> On the other hand I know someone with a stable SATA-HDD on USB converter connected
> to a Carambola2, which is something I couldn't reproduce.
> Nevertheless, it is not a filesystem corruption thing. To me it is more suspect
> to corruption in USB controller request memory and not in the bulk payload.
> However, I have no evidence to proove this theory.

When my living situation is saner I'll setup a proper test bench and
test lots of combinations. :)


-a

>> On 21 December 2015 at 21:09, Eugene Grosbein <eugen at grosbein.net> wrote:
>> > On 21.12.2015 12:02, Adrian Chadd wrote:
>> >> hi,
>> >>
>> >> I've been poking at the ci20 port to bring it up to
>> >> self-booting/running, and this involves using USB1 as a rootfs. Yeah,
>> >> I know, ohci, but that's what I have for now.
>> >>
>> >> Anyway, there was filesystem corruption, so I went digging into it and
>> >> found that we just weren't taking L2 cache line size into account when
>> >> doing the busdma bits. The JZ4780 SoC has 32 byte L1 lines, and 128
>> >> byte L2 lines. Oops
>> >>
>> >> So, two things are needed:
>> >>
>> >> * for the ci20 port, which isn't in the mainline tree yet, we need to
>> >> use USB_HOST_ALIGN=128, and
>> >> * we need to teach the busdma code about the maximum line size, not
>> >> just the L1 line size.
>> >>
>> >> Here's a diff that does the latter:
>> >>
>> >> https://people.freebsd.org/~adrian/mips/mips-fix-dcache-busdma.diff
>> >>
>> >> I'm going to test this out on my L1-only platforms (read: atheros) tomorrow.
>> >>
>> >> Does anyone have any comments?
>> >
>> > Can that be the source of my USB problems? Total system hang while doing lots of umass I/O
>> > with TP-Link TL-WDR3600? If yes, I'd like to re-run my tests with these new patches.
>
> --
> B.Walter <bernd at bwct.de> http://www.bwct.de
> Modbus/TCP Ethernet I/O Baugruppen, ARM basierte FreeBSD Rechner uvm.