Comment 10 for bug 1852510

On Fri, 15 Nov 2019 at 09:30, Hui Wang <email address hidden> wrote:
>
> I did test with VMSPLIT_2G today, the mmc/sd controller will not work
> anymore on rpi4 boards, so enable VMSPLIT_2G is not a solution so far.

Oh well, was worth a try.

> And today I also tested dwc2, it worked well, maybe we could enable dwc2
> instead of dwc_otg, then we could use a single kernel to support
> rpi2/3/4. dwc2 worked well both with VMSPLIT_2G and VMSPLIT_3G.

Interesting; I noted upstream talking about the optimization of
dwc_otg (I'm guessing, from a quick skim of each, that's mostly from
the FIQ FSM stuff in dwc_otg which dwc2 seems to lack); we should
probably benchmark the performance differences between dwc_otg and
dwc2, both USB transfer speeds, and load on the ARM during transfers
(my hunch is, if anything is affected, it'll be the latter - I vaguely
recall forum posts about improvements on the ARM load during large USB
transactions).

> I am building a formal armhf and arm64 kernel with dwc2 enabled, will
> test all kernels on all boards. And I will share the kernels to the lp,
> anyone could help test them.

Given arm64 isn't affected, would it be worth sticking with dwc_otg on
that arch? Or is the inconsistency (e.g. different capabilities?) an
issue in and of itself?

I'm more than happy to test out some kernels when they're available!

Thanks,

Dave.