Re: [PATCH next v2 3/6] usb: xhci-mtk: update fs bus bandwidth by bw_budget_table

[Ikjoon Jang <ikjn@chromium.org>]

On Fri, Aug 27, 2021 at 5:49 PM Chunfeng Yun (云春峰)
<Chunfeng.Yun@mediatek.com> wrote:
>
> On Fri, 2021-08-27 at 17:14 +0800, Ikjoon Jang wrote:
> > On Fri, Aug 27, 2021 at 2:49 PM Chunfeng Yun (云春峰)
> > <Chunfeng.Yun@mediatek.com> wrote:
> > >
> > > On Thu, 2021-08-26 at 19:54 +0800, Ikjoon Jang wrote:
> > > > Hi Chunfeng,
> > > >
> > > > On Thu, Aug 26, 2021 at 10:52 AM Chunfeng Yun <
> > > > chunfeng.yun@mediatek.com> wrote:
> > > > >
> > > > > Use @bw_budget_table[] to update fs bus bandwidth due to
> > > > > not all microframes consume @bw_cost_per_microframe, see
> > > > > setup_sch_info().
> > > > >
> > > > > Signed-off-by: Chunfeng Yun <chunfeng.yun@mediatek.com>
> > > > > ---
> > > > > v2: new patch, move from another series
> > > > > ---
> > > > >  drivers/usb/host/xhci-mtk-sch.c | 17 +++++++----------
> > > > >  1 file changed, 7 insertions(+), 10 deletions(-)
> > > > >
> > > > > diff --git a/drivers/usb/host/xhci-mtk-sch.c
> > > > > b/drivers/usb/host/xhci-mtk-sch.c
> > > > > index cffcaf4dfa9f..83abd28269ca 100644
> > > > > --- a/drivers/usb/host/xhci-mtk-sch.c
> > > > > +++ b/drivers/usb/host/xhci-mtk-sch.c
> > > > > @@ -458,8 +458,8 @@ static int check_fs_bus_bw(struct
> > > > > mu3h_sch_ep_info *sch_ep, int offset)
> > > > >                  * Compared with hs bus, no matter what ep
> > > > > type,
> > > > >                  * the hub will always delay one uframe to send
> > > > > data
> > > > >                  */
> > > > > -               for (j = 0; j < sch_ep->cs_count; j++) {
> > > > > -                       tmp = tt->fs_bus_bw[base + j] + sch_ep-
> > > > > > bw_cost_per_microframe;
> > > > >
> > > > > +               for (j = 0; j < sch_ep->num_budget_microframes;
> > > > > j++) {
> > > > > +                       tmp = tt->fs_bus_bw[base + j] + sch_ep-
> > > > > > bw_budget_table[j];
> > > >
> > > > I'm worrying about this case with two endpoints,
> > > > * EP1OUT: isochronous, maxpacket=192: bw_budget_table[] = { 188,
> > > > 188,
> > > > 0, ... }
> > > > * EP2IN: interrupt, maxpacket=64: bw_budget_table[] = { 0, 0, 64,
> > > > 64,
> > > > ... }
> > > > (Is this correct bw_budget_table contents for those eps?)
> > >
> > > Yes, ep1out isoc use two uframe, ep2in intr use a extra cs;
> > > >
> > > > I'm not sure if it's okay for those two endpoints to be allocated
> > > > on the same u-frame slot.
> > > > Can you please check if this is okay for xhci-mtk?
> > >
> > > Already test it this afternoon, can transfer data rightly on our
> > > dvt
> > > env.
> > >
> > > > (I feel like I already asked the same questions many times.)
> > >
> > > Yes, as said before, prefer to use bw_budget_table[], if there is
> > > issue, we can fix it by building this table.
> >
> > So do you mean such an allocation shouldn't be a problem by IP
> > design?
> Yes, at least on our dvt platform

Did you check that your side also has a similar allocation
(SSPLIT-all sits between SSPLIT-start ~ -end for another ep)?
My audio headset doesn't work properly with this scheme.

>
> >
> > This patch starts to allow such an allocation (again).
> > But i remember my earlier tests showed that when those two eps
> > in the above example are allocated on the same u-frame slot,
> > xhci-mtk puts "SSPLIT for EP2" between
> > "SSPLIT-start and SSPLIT-end for EP1OUT transaction",
> > which is a spec violation.
>
> Which section in usb2.0 spec?

I think that's just a basic rule - if software wants to send 192 bytes
through a full-speed bus, HC should send OUT/DATA 192 bytes
continuously without inserting any other packets during that 192 bytes.
and usb2 11.14.2 mentions that TT has separated
Start-Split and Complete-Split buffers
but not tracked each transaction per endpoint basis.

>
> > Hub will generate bit stuffing errors on the
> > full-speed bus.
> which platform?

I remember it was mt8173.

And for bit stuffing errors I mentioned in the earlier mail.
when I read the spec again, 11.21 mentions that bit stuffing error
is generated when _a microframe_ should be passed without
corresponding SSPLIT-mid/end. So this is not the case and also
I'm not sure what will happen on the full-speed bus, sorry.
In my case what I can be sure of is that the audio output was
broken with those allotments.

What is the xhci-mtk's policy when there are more than two EPs
marked as the same u-frame offset like in the above example?

>
> >
> >
> > >
> > > Thanks
> > > >
> > > >
> > > > >                         if (tmp > FS_PAYLOAD_MAX)
> > > > >                                 return -ESCH_BW_OVERFLOW;
> > > > >                 }
> > > > > @@ -534,21 +534,18 @@ static void update_sch_tt(struct
> > > > > mu3h_sch_ep_info *sch_ep, bool used)
> > > > >  {
> > > > >         struct mu3h_sch_tt *tt = sch_ep->sch_tt;
> > > > >         u32 base, num_esit;
> > > > > -       int bw_updated;
> > > > >         int i, j;
> > > > >
> > > > >         num_esit = XHCI_MTK_MAX_ESIT / sch_ep->esit;
> > > > >
> > > > > -       if (used)
> > > > > -               bw_updated = sch_ep->bw_cost_per_microframe;
> > > > > -       else
> > > > > -               bw_updated = -sch_ep->bw_cost_per_microframe;
> > > > > -
> > > > >         for (i = 0; i < num_esit; i++) {
> > > > >                 base = sch_ep->offset + i * sch_ep->esit;
> > > > >
> > > > > -               for (j = 0; j < sch_ep->cs_count; j++)
> > > > > -                       tt->fs_bus_bw[base + j] += bw_updated;
> > > > > +               for (j = 0; j < sch_ep->num_budget_microframes;
> > > > > j++)
> > > > > +                       if (used)
> > > > > +                               tt->fs_bus_bw[base + j] +=
> > > > > sch_ep-
> > > > > > bw_budget_table[j];
> > > > >
> > > > > +                       else
> > > > > +                               tt->fs_bus_bw[base + j] -=
> > > > > sch_ep-
> > > > > > bw_budget_table[j];
> > > > >
> > > > >         }
> > > > >
> > > > >         if (used)
> > > > > --
> > > > > 2.18.0
> > > > >