linux-kernel - Re: [PATCH V2 1/5] usb: serial: f81534: add high baud rate support

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Message-ID: <20180110092740.GX11344@localhost>
Date:   Wed, 10 Jan 2018 10:27:40 +0100
From:   Johan Hovold <johan@...nel.org>
To:     "Ji-Ze Hong (Peter Hong)" <hpeter@...il.com>
Cc:     Johan Hovold <johan@...nel.org>, gregkh@...uxfoundation.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        peter_hong@...tek.com.tw,
        "Ji-Ze Hong (Peter Hong)" <hpeter+linux_kernel@...il.com>
Subject: Re: [PATCH V2 1/5] usb: serial: f81534: add high baud rate support

On Wed, Jan 10, 2018 at 05:16:01PM +0800, Ji-Ze Hong (Peter Hong) wrote:
> Hi Johan,
> 
> Johan Hovold 於 2018/1/10 下午 04:49 寫道:
> >> Normally, the communication with F81534 ep0 will take less than 1 sec
> >> (even only some milliseconds), but It maybe take much long time with
> >> huge loading with UART functional.
> >>
> >> We had tested it on BurnInTest, 4 ports with 921600bps + MSR status
> >> check to perform huge loading test. The worst case to read MSR register
> >> via ep0 will take 15~18 seconds. So We'll still remain the max waiting
> >> time for access ep0 with 2x10=20s in high baud rate mode.
> > 
> > Wow, that's unfortunate. But note that your patch only doubles the
> > timeout to 2000 ms, that is, two seconds and not twenty:
> > 
> > -#define F81534_USB_TIMEOUT             1000
> > +#define F81534_USB_TIMEOUT             2000
> > 
> > If you really intended to increase this to twenty seconds, then please
> > do so in a separate (preparatory) patch where you describe why that is
> > needed (e.g. what you wrote above).
> 
> In f81534_set_register()/f81534_get_register(), We'll use a while loop
> with 10 times to get/set register and the timeout is 1000ms. So the
> total minimum retry timeout is 1000x10=10s.
> 
> But when introducing the high baud rate support, 10s is not enough for
> heavily loading. We had tested the minimum retry is 16~18s, so we
> enlarge the F81534_USB_TIMEOUT from 1000 to 2000 and the total minimum
> retry timeout is 20s.
> 
> Should I separate it as 2 patches? This issue is due to introducing
> high baud patch.

Ah, sorry. Forgot about the retries. Increasing it as part of this patch
is fine.

Johan