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

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Date:   Mon, 23 May 2022 16:55:52 +0800
From:   Chunfeng Yun <chunfeng.yun@...iatek.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.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

On Wed, 2022-05-18 at 14:01 +0200, AngeloGioacchino Del Regno wrote:
> 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?
This is usually limited into one interval; e.g. the last interval
transfers 8 bytes in fact, but I assume it may transfer 188 bytes, I
think the consumption increase can be ignored.

> 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