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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Message-ID: <BN8PR11MB3668FA6A2247710ED7DEF16EE97A9@BN8PR11MB3668.namprd11.prod.outlook.com>
Date:   Fri, 2 Sep 2022 11:57:24 +0000
From:   <Kumaravel.Thiagarajan@...rochip.com>
To:     <ilpo.jarvinen@...ux.intel.com>
CC:     <andy.shevchenko@...il.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: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> Sent: Thursday, September 1, 2022 7:12 PM
> To: Kumaravel Thiagarajan - I21417 <Kumaravel.Thiagarajan@...rochip.com>
> Cc: andy.shevchenko@...il.com; Greg Kroah-Hartman
> <gregkh@...uxfoundation.org>; Jiri Slaby <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 Wunner <lukas@...ner.de>; LKML <linux-kernel@...r.kernel.org>;
> linux-serial <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 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.

Thank You.

Regards,
Kumaravel