linux-kernel - Re: [PATCH 5/6] tty: serial: Add linflexuart driver for S32V234

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Date:   Wed, 7 Aug 2019 16:42:17 +0000
From:   Stefan-gabriel Mirea <stefan-gabriel.mirea@....com>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "corbet@....net" <corbet@....net>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "will@...nel.org" <will@...nel.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        Leo Li <leoyang.li@....com>,
        "jslaby@...e.com" <jslaby@...e.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Cosmin Stefan Stoica <cosmin.stoica@....com>,
        Larisa Ileana Grigore <larisa.grigore@....com>
Subject: Re: [PATCH 5/6] tty: serial: Add linflexuart driver for S32V234

On 8/6/2019 9:40 PM, gregkh@...uxfoundation.org wrote:
> On Tue, Aug 06, 2019 at 05:11:17PM +0000, Stefan-gabriel Mirea wrote:
>> On 8/5/2019 6:31 PM, gregkh@...uxfoundation.org wrote:
>>> On Fri, Aug 02, 2019 at 07:47:23PM +0000, Stefan-gabriel Mirea wrote:
>>>>
>>>> +/* Freescale Linflex UART */
>>>> +#define PORT_LINFLEXUART     121
>>>
>>> Do you really need this modified?
>>
>> Hello Greg,
>>
>> This macro is meant to be assigned to port->type in the config_port
>> method from uart_ops, in order for verify_port to know if the received
>> serial_struct structure was really targeted for a LINFlex port. It
>> needs to be defined outside, to avoid "collisions" with other drivers.
> 
> Yes, I know what it goes to, but does anyone in userspace actually use
> it?

No, we do not use it from userspace, but kept the pattern only for
conformance.

>> Other than that, I do not see anything wrong with the addition of a
>> define in serial_core.h for this purpose (which is also what most of the
>> serial drivers do, including amba-pl011.c, mentioned in
>> Documentation/driver-api/serial/driver.rst as providing the reference
>> implementation), so please be more specific.
> 
> I am getting tired of dealing with merge issues with that list, and no
> one seems to be able to find where they are really needed for userspace,
> especially for new devices.  What happens if you do not have use it?

I see. If I drop its usage completely and leave 'type' from the
uart_port as 0, uart_port_startup() will fail when finding that
uport->type == PORT_UNKNOWN at [1] (there may be other effects as well,
e.g. due to the check in uart_configure_port[2]).

So I suppose that I need to define some nonzero 'PORT_KNOWN' macro in
the driver and use that one internally for 'type'. Is my understanding
correct? Will there be any problems if I define it to a positive integer
which is already assigned to another driver, according to serial_core.h?

Regards,
Stefan

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/tty/serial/serial_core.c?h=v5.3-rc1#n188
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/tty/serial/serial_core.c?h=v5.3-rc1#n2348