linux-kernel - Re: [PATCH] usb: xhci-mtk: relax TT periodic bandwidth allocation

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Date:   Wed, 11 Aug 2021 07:09:48 +0000
From:   Chunfeng Yun (云春峰) 
        <Chunfeng.Yun@...iatek.com>
To:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "ikjn@...omium.org" <ikjn@...omium.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "mathias.nyman@...el.com" <mathias.nyman@...el.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH] usb: xhci-mtk: relax TT periodic bandwidth allocation

On Thu, 2021-08-05 at 13:39 +0800, Ikjoon Jang wrote:
> Currently xhci-mtk needs software-managed bandwidth allocation for
> periodic endpoints, it allocates the microframe index for the first
> start-split packet for each endpoint. As this index allocation logic
> should avoid the conflicts with other full/low-speed periodic
> endpoints,
> it uses the worst case byte budgets on high-speed bus bandwidth
> For example, for an isochronos IN endpoint with 192 bytes budget,
> it will consume the whole 4 u-frames(188 * 4) while the actual
> full-speed bus budget should be just 192bytes.
> 
> This patch changes the low/full-speed bandwidth allocation logic
> to use "approximate" best case budget for lower speed bandwidth
> management. For the same endpoint from the above example, the
> approximate best case budget is now reduced to (188 * 2) bytes.
> 
> Without this patch, many usb audio headsets with 3 interfaces
> (audio input, audio output, and HID) cannot be configured
> on xhci-mtk.
> 
> Signed-off-by: Ikjoon Jang <ikjn@...omium.org>
> ---
> 
>  drivers/usb/host/xhci-mtk-sch.c | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/usb/host/xhci-mtk-sch.c b/drivers/usb/host/xhci-
> mtk-sch.c
> index f9b4d27ce449..46cbf5d54f4f 100644
> --- a/drivers/usb/host/xhci-mtk-sch.c
> +++ b/drivers/usb/host/xhci-mtk-sch.c
> @@ -459,16 +459,17 @@ static int check_fs_bus_bw(struct
> mu3h_sch_ep_info *sch_ep, int offset)
>  	u32 num_esit, tmp;
>  	int base;
>  	int i, j;
> +	u8 uframes = DIV_ROUND_UP(sch_ep->maxpkt, FS_PAYLOAD_MAX);
>  
>  	num_esit = XHCI_MTK_MAX_ESIT / sch_ep->esit;
> +
> +	if (sch_ep->ep_type == INT_IN_EP || sch_ep->ep_type ==
> ISOC_IN_EP)
> +		offset++;
> +
>  	for (i = 0; i < num_esit; i++) {
>  		base = offset + i * sch_ep->esit;
>  
> -		/*
> -		 * 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++) {
> +		for (j = 0; j < uframes; j++) {
Please don't calculate new value, should use the value calculated by
check_sch_tt().
See usb2.0 spec Figure 11-64, sometime will use 2 extra CS.

>  			tmp = tt->fs_bus_bw[base + j] + sch_ep-
> >bw_cost_per_microframe;
>  			if (tmp > FS_PAYLOAD_MAX)
>  				return -ESCH_BW_OVERFLOW;
> @@ -546,6 +547,8 @@ static void update_sch_tt(struct mu3h_sch_ep_info
> *sch_ep, bool used)
>  	u32 base, num_esit;
>  	int bw_updated;
>  	int i, j;
> +	int offset = sch_ep->offset;
> +	u8 uframes = DIV_ROUND_UP(sch_ep->maxpkt, FS_PAYLOAD_MAX);
>  
>  	num_esit = XHCI_MTK_MAX_ESIT / sch_ep->esit;
>  
> @@ -554,10 +557,13 @@ static void update_sch_tt(struct
> mu3h_sch_ep_info *sch_ep, bool used)
>  	else
>  		bw_updated = -sch_ep->bw_cost_per_microframe;
>  
> +	if (sch_ep->ep_type == INT_IN_EP || sch_ep->ep_type ==
> ISOC_IN_EP)
> +		offset++;
> +
>  	for (i = 0; i < num_esit; i++) {
> -		base = sch_ep->offset + i * sch_ep->esit;
> +		base = offset + i * sch_ep->esit;
>  
> -		for (j = 0; j < sch_ep->cs_count; j++)
> +		for (j = 0; j < uframes; j++)
>  			tt->fs_bus_bw[base + j] += bw_updated;
>  	}
>