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

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Date:   Tue, 6 Aug 2019 17:11:17 +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 8/5/2019 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.

As far as I see, uart_set_info() will actually fail at the
"baud_base < 9600" check[1], right after calling verify_port(), when
performing an ioctl() on "/dev/console" with TIOCSSERIAL using a
serial_struct obtained with TIOCGSERIAL. This happens because this
reduced version of the LINFlex UART driver will not touch the uartclk
field of the uart_port (as there is currently no clock support).
Therefore, the linflex_config/verify_port() functions, along with the
PORT_LINFLEXUART macro, may be indeed unnecessary at this point (and
should be added later). Is this what you mean?

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.

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#n872