linux-kernel - Re: [PATCH 6/8] serial: Add Tegra Combined UART driver

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Message-ID: <513a6287-9bb3-1441-b3ea-6866f2e74c99@kapsi.fi>
Date:   Mon, 14 May 2018 10:36:35 +0300
From:   Mikko Perttunen <cyndis@...si.fi>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Mikko Perttunen <mperttunen@...dia.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jassi Brar <jassisinghbrar@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thierry Reding <thierry.reding@...il.com>,
        Jon Hunter <jonathanh@...dia.com>, araza@...dia.com,
        devicetree <devicetree@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        linux-tegra@...r.kernel.org,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6/8] serial: Add Tegra Combined UART driver

On 14.05.2018 01:20, Andy Shevchenko wrote:
> On Sun, May 13, 2018 at 9:04 PM, Mikko Perttunen <cyndis@...si.fi> wrote:
>> On 05/13/2018 05:16 PM, Andy Shevchenko wrote:
>>>
>>> On Tue, May 8, 2018 at 2:44 PM, Mikko Perttunen <mperttunen@...dia.com>
>>> wrote:
>>>>
>>>> The Tegra Combined UART (TCU) is a mailbox-based mechanism that allows
>>>> multiplexing multiple "virtual UARTs" into a single hardware serial
>>>> port. The TCU is the primary serial port on Tegra194 devices.
>>>>
>>>> Add a TCU driver utilizing the mailbox framework, as the used mailboxes
>>>> are part of Tegra HSP blocks that are already controlled by the Tegra
>>>> HSP mailbox driver.
>
>>>> +static void tegra_tcu_uart_set_mctrl(struct uart_port *port, unsigned
>>>> int mctrl)
>>>> +{
>>>
>>>
>>>> +       (void)port;
>>>> +       (void)mctrl;
>>>
>>>
>>> Huh?
>>
>>
>> The serial core calls these callbacks without checking if they are set. They
>> don't make sense for this driver so they are stubbed out.
>
> My question why do you need these ugly lines? I'm pretty sure no other
> driver with stubs using such style.

It's my personal style, being explicit about unused variables in this 
way - I don't consider them ugly. But I can certainly remove them for 
the next version.

>
>>>> +}
>
>>>> +               if (written == 3) {
>>>> +                       value |= 3 << 24;
>>>> +                       value |= BIT(26);
>>>> +                       mbox_send_message(tcu->tx, &value);
>>>
>>>
>>>> +               }
>>>
>>>
>>> (1)
>>>
>>>> +       }
>>>> +
>>>> +       if (written) {
>>>> +               value |= written << 24;
>>>> +               value |= BIT(26);
>>>> +               mbox_send_message(tcu->tx, &value);
>>>> +       }
>>>
>>>
>>> (2)
>>>
>>> These are code duplications.
>>
>>
>> Indeed - the length of the duplicated code is so short, and the instances
>> are so close to each other, that I don't find it necessary (or clearer) to
>> have an extra function.
>
> It makes sense. Consider to refactor other way w/o duplication then.

I'll see if I can refactor it out.

>
>>>> +static void tegra_tcu_uart_set_termios(struct uart_port *port,
>>>> +                                      struct ktermios *new,
>>>> +                                      struct ktermios *old)
>>>> +{
>>>> +       (void)port;
>>>> +       (void)new;
>>>> +       (void)old;
>>>> +}
>>>
>>>
>>> Remove those unused stub contents.
>>
>>
>> Sure. I had these here so that we don't get unused parameter warnings, but I
>> can just as well remove the parameter names.
>
> What warnings? How did you get them? We have them disabled as far as I
> know even with W=1.

May be - it's just a habit, maybe from other projects where the warning 
is enabled.

>
>>
>>>
>>>> +       return uart_set_options(&tegra_tcu_uart_port, cons,
>>>> +                               115200, 'n', 8, 'n');
>>>
>>>
>>> Can't it be one line?
>>
>>
>> It would be a total of 81 characters in length on one line, so no.
>
> So, yes. 1 character doesn't prevent us make the readability better.
> Please, put to one line.
>

Ok, I'll change this.

Thanks,
Mikko