linux-kernel - Re: [PATCH 08/11] usb: xhci-mtk: update fs bus bandwidth by bw_budget

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Message-ID: <CAATdQgDWkohpzgr=z+uzro4m9Bd=v88DNnJ-M88-5-0annhH_w@mail.gmail.com>
Date:   Tue, 3 Aug 2021 14:05:18 +0800
From:   Ikjoon Jang <ikjn@...omium.org>
To:     Chunfeng Yun <chunfeng.yun@...iatek.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-usb@...r.kernel.org,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-arm-kernel@...ts.infradead.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Eddie Hung <eddie.hung@...iatek.com>
Subject: Re: [PATCH 08/11] usb: xhci-mtk: update fs bus bandwidth by bw_budget_table

Hi Chunfeng,

On Fri, Jul 30, 2021 at 4:51 PM 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>
> ---
>  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 0bb1a6295d64..10c0f0f6461f 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];
>                         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];

I agree that xhci-mtk-sch still has more rooms for tt periodic bandwidth
but I think this approach could trigger a problem.

for example, if there are two endpoints scheduled in the same u-frame index,
* ep1out  = iso 192bytes bw_budget_table[] = { 188, 188, 0, ...} --> y0
* ep2in = int 64bytes, bw_budget_table[] = { 0, 0, 64, ... }  --> y0

(If this is possible allocation from this patch),
I guess xhci-mtk could have some problems on internal scheduling?

>         }
>
>         if (used)

> --
> 2.18.0
>