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

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Message-ID: <18d4171a-1e1a-5476-dc9d-02a522cbf077@gmail.com>
Date:   Wed, 10 Jan 2018 13:30:18 +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 2018/1/9 下午 07:08 寫道:
> On Thu, Jan 04, 2018 at 10:29:17AM +0800, Ji-Ze Hong (Peter Hong) wrote:
>> The F81532/534 had 4 clocksource 1.846/18.46/14.77/24MHz and baud rates
>> can be up to 1.5Mbits with 24MHz.
>>
>> This device may generate data overrun when baud rate setting to 921600bps
>> or higher with old UART trigger level setting (8x14=112) with full
>> loading. We'll change trigger level from 8x14=112 to 8x8=64 to avoid data
>> overrun.
>>
>> Also the read/write of EP0 will be affected by this patch. The worst case
>> of responding time is 20s when all serial port are full loading and trying
>> to access EP0, so we change EP0 timeout from 10 to 20s.
> 
> Surely you meant 1 and 2 seconds respectively here? And if you have
> indeed measured response times close to 2000 ms then perhaps you want to
> add even more margin?

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.

Thanks
-- 
With Best Regards,
Peter Hong