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 <9W76KR.NVDSVG4IWZ3A3@crapouillou.net>
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From:   Siarhei Volkau <lis8215@gmail.com>
Date:   Sun, 23 Oct 2022 08:29:45 +0300
Message-ID: <CAKNVLfZmUpFzKsdzY1e_mUTVsM-jnL65Fi6EXYcF80-oNV+DGQ@mail.gmail.com>
Subject: Re: [PATCH v3 2/2] serial: 8250/ingenic: Add support for the JZ4750/JZ4755
To:     Paul Cercueil <paul@crapouillou.net>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Jiri Slaby <jirislaby@kernel.org>,
        linux-serial@vger.kernel.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org
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=D1=81=D0=B1, 22 =D0=BE=D0=BA=D1=82. 2022 =D0=B3. =D0=B2 23:07, Paul Cercue=
il <paul@crapouillou.net>:
>
> Hi Siarhei,
>
> Le sam. 22 oct. 2022 =C3=A0 19:50:47 +0300, Siarhei Volkau
> <lis8215@gmail.com> a =C3=A9crit :
> > 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_ser=
ial.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 =3D 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 =3D &dev->port;
> >       unsigned int divisor;
> >       int baud =3D 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 =3D dev->baud;
> >       divisor =3D 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 /=3D 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.

> > +
> > +     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 =3D {
> >
> >  static const struct of_device_id of_match[] =3D {
> >       { .compatible =3D "ingenic,jz4740-uart", .data =3D &jz4740_uart_c=
onfig
> > },
> > +     { .compatible =3D "ingenic,jz4750-uart", .data =3D &jz4760_uart_c=
onfig
> > },
> >       { .compatible =3D "ingenic,jz4760-uart", .data =3D &jz4760_uart_c=
onfig
> > },
> >       { .compatible =3D "ingenic,jz4770-uart", .data =3D &jz4760_uart_c=
onfig
> > },
> >       { .compatible =3D "ingenic,jz4775-uart", .data =3D &jz4760_uart_c=
onfig
> > },
> > --
> > 2.36.1
> >
>
>