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

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Date:   Fri, 27 Aug 2021 17:14:17 +0800
From:   Ikjoon Jang <ikjn@...omium.org>
To:     Chunfeng Yun (云春峰) 
        <Chunfeng.Yun@...iatek.com>
Cc:     "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Yaqii Wu (武亚奇) <Yaqii.Wu@...iatek.com>,
        "mathias.nyman@...el.com" <mathias.nyman@...el.com>,
        Eddie Hung (洪正鑫) 
        <Eddie.Hung@...iatek.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>
Subject: Re: [PATCH next v2 3/6] usb: xhci-mtk: update fs bus bandwidth by bw_budget_table

On Fri, Aug 27, 2021 at 2:49 PM Chunfeng Yun (云春峰)
<Chunfeng.Yun@...iatek.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@...iatek.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@...iatek.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?

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. Hub will generate bit stuffing errors on the
full-speed bus.


>
> 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
> > >