linux-kernel - Re: [PATCH 1/2] usb: xhci-mtk: fix fs isoc's transfer error

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Message-ID: <7781eaaf-ad09-7283-dbb8-69d0fb3f1d14@collabora.com>
Date:   Wed, 18 May 2022 14:01:20 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Mathias Nyman <mathias.nyman@...el.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-usb@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Eddie Hung <eddie.hung@...iatek.com>,
        Tianping Fang <tianping.fang@...iatek.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH 1/2] usb: xhci-mtk: fix fs isoc's transfer error

Il 12/05/22 08:49, Chunfeng Yun ha scritto:
> Due to the scheduler allocates the optimal bandwidth for FS ISOC endpoints,
> this may be not enough actually and causes data transfer error, so come up
> with an estimate that is no less than the worst case bandwidth used for
> any one mframe, but may be an over-estimate.
> 
> Fixes: 451d3912586a ("usb: xhci-mtk: update fs bus bandwidth by bw_budget_table")
> Cc: stable@...r.kernel.org
> Signed-off-by: Chunfeng Yun <chunfeng.yun@...iatek.com>

Hello Chunfeng,
I agree this is "a fix"... but is it the best fix?

Shooting the bandwidth very high will have power consumption consequences, are
those measurable?
And if they are, what is the expected power consumption increase in percentage
(and/or microamperes)? Also, out of the expected increase, have you got any
measurement for that?

Assuming that the measurement is done for one SoC, it's possible to make some
assumption about a different part.

Regards,
Angelo

> ---
>   drivers/usb/host/xhci-mtk-sch.c | 16 +++++++---------
>   1 file changed, 7 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/usb/host/xhci-mtk-sch.c b/drivers/usb/host/xhci-mtk-sch.c
> index f3139ce7b0a9..953d2cd1d4cc 100644
> --- a/drivers/usb/host/xhci-mtk-sch.c
> +++ b/drivers/usb/host/xhci-mtk-sch.c