linux-kernel - Re: [PATCH v10 10/10] tty: serial: Add Nuvoton ma35d1 serial driver support

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Message-Id: <72983689-0e98-4482-b549-ba2530274943@app.fastmail.com>
Date:   Tue, 09 May 2023 14:32:12 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     "Jacky Huang" <ychuang570808@...il.com>,
        "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>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "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, LKML <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        linux-serial <linux-serial@...r.kernel.org>, schung@...oton.com,
        mjchen@...oton.com, "Jacky Huang" <ychuang3@...oton.com>
Subject: Re: [PATCH v10 10/10] tty: serial: Add Nuvoton ma35d1 serial driver support

On Tue, May 9, 2023, at 14:25, Ilpo Järvinen wrote:
> On Tue, 9 May 2023, Arnd Bergmann wrote:
>> On Tue, May 9, 2023, at 12:17, Ilpo Järvinen wrote:
>> > On Mon, 8 May 2023, Jacky Huang wrote:
>> >> +
>> >> +#define UART_NR			17
>> >> +
>> >> +#define UART_REG_RBR		0x00
>> >> +#define UART_REG_THR		0x00
>> >> +#define UART_REG_IER		0x04
>> >> +#define UART_REG_FCR		0x08
>> >> +#define UART_REG_LCR		0x0C
>> >> +#define UART_REG_MCR		0x10
>> >
>> > These duplicate include/uapi/linux/serial_reg.h ones, use the std ones 
>> > directly.
>> >
>> > Setup regshift too and use it in serial_in.
>> 
>> I think this came up in previous reviews, but it turned out that
>> only the first six registers are compatible, while the later
>> ones are all different, and it's not 8250 compatible.
>
> So use the normal name for compatible ones and HW specific names for the 
> others?
>
> It might not be compatible in everything but surely 8250 influence is 
> visible here and there.

I'd rename all of them and share nothing. I had the same thought as you
when I first looked at the driver, and thought of how we merged the omap
uart into 8250 for this reason, but after I found a datasheet for this
one, my impression was that it's a much more distant cousin of 8250
than the others,

There is clearly some family lineage, but there are differences
everywhere, and I don't think it was designed by extending a 8250
compatible hardware block with extra features, but rather built
from scratch (sigh) based only loosely on a register description
but then extending it with no intent of retaining compatibility.

       Arnd