linux-kernel - Re: [PATCH v14 1/1] tty: serial: Add Nuvoton ma35d1 serial driver support

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Message-ID: <4fd20e8d-49fd-be07-e4e5-0860fdb07125@gmail.com>
Date:   Thu, 15 Jun 2023 18:46:01 +0800
From:   Jacky Huang <ychuang570808@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>
Cc:     Rob Herring <robh+dt@...nel.org>,
        krzysztof.kozlowski+dt@...aro.org, Lee Jones <lee@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Jiri Slaby <jirislaby@...nel.org>,
        Tomer Maimon <tmaimon77@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, devicetree@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-serial@...r.kernel.org,
        soc@...nel.org, schung@...oton.com, mjchen@...oton.com,
        Jacky Huang <ychuang3@...oton.com>
Subject: Re: [PATCH v14 1/1] tty: serial: Add Nuvoton ma35d1 serial driver
 support



On 2023/6/15 下午 06:19, Greg Kroah-Hartman wrote:
> On Tue, Jun 13, 2023 at 05:44:23PM +0200, Arnd Bergmann wrote:
>> On Tue, Jun 13, 2023, at 16:49, Greg KH wrote:
>>> On Tue, Jun 13, 2023 at 06:58:32PM +0800, Jacky Huang wrote:
>>>> On 2023/6/13 下午 06:28, Greg KH wrote:
>>>>> On Mon, Jun 12, 2023 at 02:53:55AM +0000, Jacky Huang wrote:
>>>>>> From: Jacky Huang <ychuang3@...oton.com>
>>>>>>
>>>>>> This adds UART and console driver for Nuvoton ma35d1 Soc.
>>>>>> It supports full-duplex communication, FIFO control, and
>>>>>> hardware flow control.
>>>>> You get a full 72 columns for your changelog :)
>>>>>
>>>>>> --- a/include/uapi/linux/serial_core.h
>>>>>> +++ b/include/uapi/linux/serial_core.h
>>>>>> @@ -279,4 +279,7 @@
>>>>>>    /* Sunplus UART */
>>>>>>    #define PORT_SUNPLUS	123
>>>>>> +/* Nuvoton MA35 SoC */
>>>>>> +#define PORT_MA35	124
>>>>>> +
>>>>> Why is this change needed?  What userspace code is going to rely on it?
>>>>>
>>>>> thanks,
>>>>>
>>>>> greg k-h
>>>> Because the serial driver requires a port->type, and almost all serial
>>>> drivers defined their port type here. We follow the practice of most serial
>>>> drivers here.
>>>> If we don't do it this way, we would have to directly assign a value to
>>>> port->type. However, such modifications were questioned in the past,
>>>> which is why we changed it back to defining the port type in serial_core.h.
>>> I really really want to get rid of this list, as it's a UAPI that no one
>>> uses.  So please don't use it, it doesn't help anything, and while the
>>> serial driver might require it, it doesn't actually do anything with
>>> that field, right?  So why don't we just set all of the values to the
>>> same one?
>> I don't see how Jacky can come up with a patch to do this correctly
>> without more specific guidance to what exactly you are looking for,
>> after the last 123 people that added support for a new port got
>> that merged.
> I keep complaining about this, when I notice it.  Just use the "default"
> port type in the serial driver and don't add a new type here and it
> should just work, right?
>
>> I checked debian codesearch and found only three obscure packages that
>> accidentally include this header instead of including linux/serial.h,
>> a couple of lists of all kernel headers, and none that include it on
>> purpose. I agree that this header should really not exist in uapi,
>> but the question is what exactly to do about it.
>>
>> Possible changes would be:
>>
>> - add a special value PORT_* constant other than PORT_UNKNOWN that
>>    can be used by serial drivers instead of a unique value, and
>>    ensure that the serial core can handle drivers using it.
> Why do we need a special constant?
>
>> - move all values used by the 8250 driver from serial_core.h
>>    to serial.h, as this driver actually uses the constants.
> Makes sense.
>
>> - Move the remaining contents of uapi/linux/serial.h into the
>>    non-uapi version.
>>
>> - Change all drivers that only reference a single PORT_*
>>    value to use the generic one.
> I think this is the best thing to do.
>
> thanks,
>
> greg k-h

I will remove the definition of PORT_MA35 without modifying serial_core.h.

However, we still need to assign a value to port->type. So, can we follow
the approach used in the LiteUART driver and directly assign port->type = 1?


Best regards,
Jacky Huang