Re: [PATCH v3 2/2] serial: 8250/ingenic: Add support for the JZ4750/JZ4755

[Paul Cercueil <paul@crapouillou.net>]

Hi,

Le dim. 23 oct. 2022 à 08:29:45 +0300, Siarhei Volkau 
<lis8215@gmail.com> a écrit :
> сб, 22 окт. 2022 г. в 23:07, Paul Cercueil 
> <paul@crapouillou.net>:
>> 
>>  Hi Siarhei,
>> 
>>  Le sam. 22 oct. 2022 à 19:50:47 +0300, Siarhei Volkau
>>  <lis8215@gmail.com> a écrit :
>>  > JZ4750/55/60 (but not JZ4760b) have an extra divisor in between 
>> extclk
>>  > and peripheral clock, called CPCCR.ECS, the driver can't figure 
>> out
>>  > the
>>  > real state of the divisor without dirty hack - peek CGU CPCCR
>>  > register.
>>  > However, we can rely on a vendor's bootloader (u-boot 1.1.6) 
>> behavior:
>>  > if (extclk > 16MHz)
>>  >     the divisor is enabled, so the UART driving clock is extclk/2.
>>  >
>>  > This behavior relies on hardware differences: most boards (if not 
>> all)
>>  > with those SoCs have 12 or 24 MHz oscillators but many peripherals
>>  > want
>>  > 12Mhz to operate properly (AIC and USB-PHY at least).
>>  >
>>  > The patch doesn't affect JZ4760's behavior as it is subject for
>>  > another
>>  > patchset with re-classification of all supported ingenic UARTs.
>>  >
>>  > Link:
>>  > 
>> https://github.com/carlos-wong/uboot_jz4755/blob/master/cpu/mips/jz_serial.c#L158
>>  > Signed-off-by: Siarhei Volkau <lis8215@gmail.com>
>>  > ---
>>  >  drivers/tty/serial/8250/8250_ingenic.c | 48
>>  > ++++++++++++++++++++++----
>>  >  1 file changed, 42 insertions(+), 6 deletions(-)
>>  >
>>  > diff --git a/drivers/tty/serial/8250/8250_ingenic.c
>>  > b/drivers/tty/serial/8250/8250_ingenic.c
>>  > index 2b2f5d8d2..744705467 100644
>>  > --- a/drivers/tty/serial/8250/8250_ingenic.c
>>  > +++ b/drivers/tty/serial/8250/8250_ingenic.c
>>  > @@ -87,24 +87,19 @@ static void __init
>>  > ingenic_early_console_setup_clock(struct earlycon_device *dev
>>  >       dev->port.uartclk = be32_to_cpup(prop);
>>  >  }
>>  >
>>  > -static int __init ingenic_early_console_setup(struct 
>> earlycon_device
>>  > *dev,
>>  > +static int __init ingenic_earlycon_setup_tail(struct 
>> earlycon_device
>>  > *dev,
>>  >                                             const char *opt)
>>  >  {
>>  >       struct uart_port *port = &dev->port;
>>  >       unsigned int divisor;
>>  >       int baud = 115200;
>>  >
>>  > -     if (!dev->port.membase)
>>  > -             return -ENODEV;
>>  > -
>>  >       if (opt) {
>>  >               unsigned int parity, bits, flow; /* unused for now 
>> */
>>  >
>>  >               uart_parse_options(opt, &baud, &parity, &bits, 
>> &flow);
>>  >       }
>>  >
>>  > -     ingenic_early_console_setup_clock(dev);
>>  > -
>>  >       if (dev->baud)
>>  >               baud = dev->baud;
>>  >       divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * baud);
>>  > @@ -129,9 +124,49 @@ static int __init
>>  > ingenic_early_console_setup(struct earlycon_device *dev,
>>  >       return 0;
>>  >  }
>>  >
>>  > +static int __init ingenic_early_console_setup(struct 
>> earlycon_device
>>  > *dev,
>>  > +                                           const char *opt)
>>  > +{
>>  > +     if (!dev->port.membase)
>>  > +             return -ENODEV;
>>  > +
>>  > +     ingenic_early_console_setup_clock(dev);
>>  > +
>>  > +     return ingenic_earlycon_setup_tail(dev, opt);
>>  > +}
>>  > +
>>  > +static int __init jz4750_early_console_setup(struct 
>> earlycon_device
>>  > *dev,
>>  > +                                          const char *opt)
>>  > +{
>>  > +     if (!dev->port.membase)
>>  > +             return -ENODEV;
>>  > +
>>  > +     /*
>>  > +      * JZ4750/55/60 (not JZ4760b) have an extra divisor
>>  > +      * between extclk and peripheral clock, the
>>  > +      * driver can't figure out the real state of the
>>  > +      * divisor without dirty hacks (peek CGU register).
>>  > +      * However, we can rely on a vendor's behavior:
>>  > +      * if (extclk > 16MHz)
>>  > +      *   the divisor is enabled.
>>  > +      * This behavior relies on hardware differences:
>>  > +      * most boards with those SoCs have 12 or 24 MHz
>>  > +      * oscillators but many peripherals want 12Mhz
>>  > +      * to operate properly (AIC and USB-phy at least).
>>  > +      */
>>  > +     ingenic_early_console_setup_clock(dev);
>>  > +     if (dev->port.uartclk > 16000000)
>>  > +             dev->port.uartclk /= 2;
>> 
>>  I don't understand, didn't we came up to the conclusion in your V1 
>> that
>>  it was better to force-enable the EXT/2 divider in the ingenic init
>>  code?
>> 
>>  -Paul
>> 
> 
> That was better at that moment. I dived deeper in the situation and 
> found
> a more simple and universal solution, as I think.
> Your proposal doesn't cover following situations:
>  - JZ475x with 12MHz crystal
>  - JZ4760 with 24MHz crystal
> which are legal and might appear in some hardware.

Do you have such hardware?

Don't add support for cases you can't test.

For what we know - all JZ475x use a 24 MHz crystal and all JZ4760(B) 
use a 12 MHz crystal, until proven otherwise.

-Paul

>>  > +
>>  > +     return ingenic_earlycon_setup_tail(dev, opt);
>>  > +}
>>  > +
>>  >  OF_EARLYCON_DECLARE(jz4740_uart, "ingenic,jz4740-uart",
>>  >                   ingenic_early_console_setup);
>>  >
>>  > +OF_EARLYCON_DECLARE(jz4750_uart, "ingenic,jz4750-uart",
>>  > +                 jz4750_early_console_setup);
>>  > +
>>  >  OF_EARLYCON_DECLARE(jz4770_uart, "ingenic,jz4770-uart",
>>  >                   ingenic_early_console_setup);
>>  >
>>  > @@ -328,6 +363,7 @@ static const struct ingenic_uart_config
>>  > x1000_uart_config = {
>>  >
>>  >  static const struct of_device_id of_match[] = {
>>  >       { .compatible = "ingenic,jz4740-uart", .data = 
>> &jz4740_uart_config
>>  > },
>>  > +     { .compatible = "ingenic,jz4750-uart", .data = 
>> &jz4760_uart_config
>>  > },
>>  >       { .compatible = "ingenic,jz4760-uart", .data = 
>> &jz4760_uart_config
>>  > },
>>  >       { .compatible = "ingenic,jz4770-uart", .data = 
>> &jz4760_uart_config
>>  > },
>>  >       { .compatible = "ingenic,jz4775-uart", .data = 
>> &jz4760_uart_config
>>  > },
>>  > --
>>  > 2.36.1
>>  >
>> 
>>