linux-kernel - Re: [TRIVIAL PATCH] usb/serial.h: Increase max number of serial ports per USB-serial device

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Date:	Fri, 3 Jul 2015 10:49:32 +0200
From:	Bartosz Tomeczko <bartosz.tomeczko@...il.com>
To:	Johan Hovold <johan@...nel.org>
Cc:	linux-kernel@...r.kernel.org, trivial@...nel.org
Subject: Re: [TRIVIAL PATCH] usb/serial.h: Increase max number of serial ports
 per USB-serial device

2015-07-03 10:28 GMT+02:00 Johan Hovold <johan@...nel.org>:
> On Thu, Jul 02, 2015 at 05:13:47PM +0200, Bartosz Tomeczko wrote:
>> Hello,
>>
>> I am using MOXA USB-to-serial converter with 16 serial ports. This
>> device is namely a MOXA UPort 1650-16. This device works as a simple
>> usb-serial adapter and therefore its driver uses
>> include/linux/usb/serial.h file. In this very file however maximal
>> number of serial ports served by the driver is eight (MAX_NUM_PORTS).
>> I would like to propose a trivial patch which would allow MOXA users
>> to use all ports of the device instead of just having eight of them
>> usable (as it is right now). Trivial change which might be applied on
>> the top of (4da3064d1775810f10f7ddc1c34c3f1ff502a654) is as follows:
>>
>> diff --git a/include/linux/usb/serial.h b/include/linux/usb/serial.h
>> index 704a1ab..b7af736 100644
>> --- a/include/linux/usb/serial.h
>> +++ b/include/linux/usb/serial.h
>> @@ -20,7 +20,7 @@
>>  #include <linux/kfifo.h>
>>
>>  /* The maximum number of ports one device can grab at once */
>> -#define MAX_NUM_PORTS          8
>> +#define MAX_NUM_PORTS          16
>>
>>  /* parity check flag */
>>  #define RELEVANT_IFLAG(iflag)  (iflag & (IGNBRK|BRKINT|IGNPAR|PARMRK|INPCK))
>
> I'm aware that this limit is too low be able to use all ports on that
> Moxa device. I have some patches lying around that I never got to finish
> that clean up the descriptor handling and removes the arbitrary port
> limitation completely.
>
> Let me revisit those, and I'll make sure this gets fixed for 4.3.
>
> Thanks,
> Johan

Hello Johan,

Thanks for that! So we are staying tuned for upcoming changes.
Meanwhile we will keep our kernel patched locally to support more that
eight ports.

Have a nice day.
Bartosz
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