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

[Eugene Grosbein]

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.