linux-kernel - RE: [PATCH v1 tty-next 1/2] 8250: microchip: pci1xxxx: Add driver for the quad-uart function in the multi-function endpoint of pci1xxxx device.

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Date:   Mon, 5 Sep 2022 12:01:12 +0000
From:   <Kumaravel.Thiagarajan@...rochip.com>
To:     <andy.shevchenko@...il.com>
CC:     <ilpo.jarvinen@...ux.intel.com>, <gregkh@...uxfoundation.org>,
        <jirislaby@...nel.org>, <u.kleine-koenig@...gutronix.de>,
        <johan@...nel.org>, <wander@...hat.com>,
        <etremblay@...tech-controls.com>, <macro@...am.me.uk>,
        <geert+renesas@...der.be>, <jk@...abs.org>,
        <phil.edworthy@...esas.com>, <lukas@...ner.de>,
        <linux-kernel@...r.kernel.org>, <linux-serial@...r.kernel.org>,
        <UNGLinuxDriver@...rochip.com>
Subject: RE: [PATCH v1 tty-next 1/2] 8250: microchip: pci1xxxx: Add driver for
 the quad-uart function in the multi-function endpoint of pci1xxxx device.

> -----Original Message-----
> From: Andy Shevchenko <andy.shevchenko@...il.com>
> Sent: Friday, September 2, 2022 8:33 PM
> To: Kumaravel Thiagarajan - I21417 <Kumaravel.Thiagarajan@...rochip.com>
> Cc: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>; Greg Kroah-Hartman
> <gregkh@...uxfoundation.org>; Jiri Slaby <jirislaby@...nel.org>; Uwe
> Kleine-König <u.kleine-koenig@...gutronix.de>; Johan Hovold
> <johan@...nel.org>; Wander Lairson Costa <wander@...hat.com>; Eric
> Tremblay <etremblay@...tech-controls.com>; Maciej W. Rozycki
> <macro@...am.me.uk>; Geert Uytterhoeven <geert+renesas@...der.be>;
> Jeremy Kerr <jk@...abs.org>; Phil Edworthy <phil.edworthy@...esas.com>;
> Lukas Wunner <lukas@...ner.de>; Linux Kernel Mailing List <linux-
> kernel@...r.kernel.org>; open list:SERIAL DRIVERS <linux-
> serial@...r.kernel.org>; UNGLinuxDriver
> <UNGLinuxDriver@...rochip.com>
> Subject: Re: [PATCH v1 tty-next 1/2] 8250: microchip: pci1xxxx: Add driver for
> the quad-uart function in the multi-function endpoint of pci1xxxx device.
>  
> On Fri, Sep 2, 2022 at 2:57 PM <Kumaravel.Thiagarajan@...rochip.com>
> wrote:
> > > -----Original Message-----
> > > From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> > > Sent: Thursday, September 1, 2022 7:12 PM On Thu, 1 Sep 2022,
> > > Kumaravel.Thiagarajan@...rochip.com wrote:
> 
> ...
> 
> > > > > > +       const unsigned int standard_baud_list[] = {50, 75,
> > > > > > + 110, 134, 150,
> > > 300,
> > > > > > +                                               600, 1200, 1800, 2000, 2400, 3600,
> > > > > > +                                               4800, 7200, 9600, 19200, 38400, 57600,
> > > > > > +                                               115200, 125000, 136400, 150000, 166700,
> > > > > > +                                               187500, 214300, 250000, 300000, 375000,
> > > > > > +                                               500000,
> > > > > > + 750000, 1000000, 1500000};
> > > > >
> > > > > Why?!
> > > >
> > > > The standard baud rates are handled within
> > > > serial8250_do_set_termios which is invoked from within
> mchp_pci1xxxx_set_termios in first place.
> > > > Hence if it matches with any of the standard baudrates, it can
> > > > return immediately.
> > >
> > > Care to explain why the baudrates in your table don't match those in
> > > tty_baudrate.c? ...It makes no sense to me that you call these
> > > "standard baud rates".
> > The baudrates in my table are from our legacy UART IP and these
> > baudrates can be generated by the hardware by updating UART_DLL &
> > UART_DLM alone as done by the serial8250_do_set_termios.
> > I noticed that some of the baud rates in tty_baudrate.c arenot listed
> > in this table but will still be handled by the mchp_pci1xxxx_set_termios.
> > I can rename standard_baud_list to simply baud_list. Please let me know.
> 
> No, the point is avoid repeating what standard APIs already do. Just make
> sure you call it properly and provide _get/_set_divisor() callbacks. Note, your
> driver can cope with BOTHER and there all non-standard baud rates go.
I will review my driver again and get back to you if required.

Thank You.

Regards,
Kumaravel