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.

[Kumaravel.Thiagarajan]

> -----Original Message-----
> From: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
> Sent: Wednesday, August 31, 2022 3:13 PM
> To: Kumaravel Thiagarajan - I21417 <Kumaravel.Thiagarajan@xxxxxxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>; Jiri Slaby
> <jirislaby@xxxxxxxxxx>; andy.shevchenko@xxxxxxxxx; u.kleine-
> koenig@xxxxxxxxxxxxxx; johan@xxxxxxxxxx; wander@xxxxxxxxxx;
> etremblay@xxxxxxxxxxxxxxxxxxxx; macro@xxxxxxxxxxx;
> geert+renesas@xxxxxxxxx; jk@xxxxxxxxxx; phil.edworthy@xxxxxxxxxxx;
> Lukas Wunner <lukas@xxxxxxxxx>; LKML <linux-kernel@xxxxxxxxxxxxxxx>;
> linux-serial <linux-serial@xxxxxxxxxxxxxxx>; UNGLinuxDriver
> <UNGLinuxDriver@xxxxxxxxxxxxx>
> 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 Tue, 30 Aug 2022, Kumaravel Thiagarajan wrote:
> 
> > pci1xxxx is a PCIe switch with a multi-function endpoint on one of its
> > downstream ports. Quad-uart is one of the functions in the
> > multi-function endpoint. This driver loads for the quad-uart and
> > enumerates single or multiple instances of uart based on the PCIe
> > subsystem device ID.
> >
> > Signed-off-by: Kumaravel Thiagarajan
> > <kumaravel.thiagarajan@xxxxxxxxxxxxx>
> > ---
> 
> > +static int mchp_pci1xxxx_rs485_config(struct uart_port *port,
> > +                                   struct ktermios *termios,
> > +                                   struct serial_rs485 *rs485) {
> > +     u8 data = 0;
> > +
> > +     memset(rs485->padding, 0, sizeof(rs485->padding));
> > +     rs485->flags &= SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND;
> > +
> > +     if (rs485->flags & SER_RS485_ENABLED) {
> > +             data = ADCL_CFG_EN | ADCL_CFG_PIN_SEL;
> > +             if (!(rs485->flags & SER_RS485_RTS_ON_SEND)) {
> > +                     data |= ADCL_CFG_POL_SEL;
> > +                     rs485->flags |=  SER_RS485_RTS_AFTER_SEND;
> > +             }
> > +     }
> > +
> > +     rs485->delay_rts_after_send = 0;
> > +     rs485->delay_rts_before_send = 0;
> > +     writeb(data, (port->membase + ADCL_CFG_REG));
> > +     port->rs485 = *rs485;
> 
> Most of this will be handled for by the core so don't duplicate it in the driver.
Ok. I will review and modify this if as required.

> 
> These days, you also need to provide rs485_supported.
Ok. I will modify this.

> 
> > +     return 0;
> > +}
> > +
> > +static void mchp_pci1xxxx_set_termios(struct uart_port *port,
> > +                                   struct ktermios *termios,
> > +                                   struct ktermios *old) {
> > +     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};
> > +     unsigned int baud = tty_termios_baud_rate(termios);
> > +     unsigned int baud_clock;
> > +     unsigned int quot;
> > +     unsigned int frac;
> > +     unsigned int i;
> > +
> > +     baud = tty_termios_baud_rate(termios);
> 
> Either this or the one at the declaration is redundant.
Yes. It is a mistake. I will modify.

> 
> > +     serial8250_do_set_termios(port, termios, NULL);
> > +
> > +     if (baud == 38400 && (port->flags & UPF_SPD_MASK) ==
> UPF_SPD_CUST) {
> > +             writel((port->custom_divisor & 0x3FFFFFFF),
> > +                    (port->membase + CLK_DIVISOR_REG));
> > +     } else {
> > +             for (i = 0; i < ARRAY_SIZE(standard_baud_list); i++) {
> > +                     if (baud == standard_baud_list[i])
> > +                             return;
> 
> Did you mean to break here instead?
No. 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. 

> 
> > +             }
> > +             tty_termios_encode_baud_rate(termios, baud, baud);
> > +
> > +             baud = uart_get_baud_rate(port, termios, old,
> > +                                       50, 1500000);
> > +             baud_clock = readb(port->membase + CLK_SEL_REG);
> > +
> > +             if ((baud_clock & CLK_SEL_MASK) == CLK_SEL_500MHZ) {
> > +                     quot = 500000000 / (16 * baud);
> > +                     writel(quot, (port->membase + CLK_DIVISOR_REG));
> > +             } else if ((baud_clock & CLK_SEL_MASK) == CLK_SEL_166MHZ) {
> > +                     quot = (166667 * 1000) / (16 * baud);
> > +                     writel(quot, (port->membase + CLK_DIVISOR_REG));
> > +             } else {
> > +                     quot = ((1000000000) / (baud * UART_BIT_SAMPLE_CNT));
> > +                     frac = (((1000000000 - (quot * baud *
> > +                             UART_BIT_SAMPLE_CNT)) / UART_BIT_SAMPLE_CNT)
> > +                             * 255) / baud;
> > +                     writel(frac | (quot << 8),
> > +                            (port->membase + CLK_DIVISOR_REG));
> > +             }
> 
> Please check ->[gs]et_divisor() out.
Ok. I will review and get back to you.

Thank You.

Regards,
Kumaravel