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

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Date:   Wed, 10 Jan 2018 17:16:01 +0800
From:   "Ji-Ze Hong (Peter Hong)" <hpeter@...il.com>
To:     Johan Hovold <johan@...nel.org>
Cc:     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

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.

Thanks
-- 
With Best Regards,
Peter Hong