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From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Fri, 2 Sep 2022 18:02:34 +0300
Message-ID: <CAHp75VfUq-JkfjD1YOj_+ST-eK=aW=8LoHOUW4zqpeA_QUZbyw@mail.gmail.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.
To:     Kumaravel Thiagarajan - I21417 
        <Kumaravel.Thiagarajan@microchip.com>
Cc:     =?UTF-8?Q?Ilpo_J=C3=A4rvinen?= <ilpo.jarvinen@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        =?UTF-8?Q?Uwe_Kleine=2DK=C3=B6nig?= 
        <u.kleine-koenig@pengutronix.de>, Johan Hovold <johan@kernel.org>,
        Wander Lairson Costa <wander@redhat.com>,
        Eric Tremblay <etremblay@distech-controls.com>,
        "Maciej W. Rozycki" <macro@orcam.me.uk>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Jeremy Kerr <jk@ozlabs.org>,
        Phil Edworthy <phil.edworthy@renesas.com>,
        Lukas Wunner <lukas@wunner.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@vger.kernel.org>,
        Microchip Linux Driver Support <UNGLinuxDriver@microchip.com>
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On Fri, Sep 2, 2022 at 2:57 PM <Kumaravel.Thiagarajan@microchip.com> wrote:
> > -----Original Message-----
> > From: Ilpo J=C3=A4rvinen <ilpo.jarvinen@linux.intel.com>
> > Sent: Thursday, September 1, 2022 7:12 PM
> > On Thu, 1 Sep 2022, Kumaravel.Thiagarajan@microchip.com wrote:

...

> > > > > +       const unsigned int standard_baud_list[] =3D {50, 75, 110,=
 134, 150,
> > 300,
> > > > > +                                               600, 1200, 1800, =
2000, 2400, 3600,
> > > > > +                                               4800, 7200, 9600,=
 19200, 38400, 57600,
> > > > > +                                               115200, 125000, 1=
36400, 150000, 166700,
> > > > > +                                               187500, 214300, 2=
50000, 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 "standar=
d
> > 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 b=
y 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.

--=20
With Best Regards,
Andy Shevchenko