Re: [PATCH v2] Revert "tty: serial: meson: Add a earlycon for the T7 SoC"

[Dmitry Rokosov]

On Mon, Aug 28, 2023 at 10:23:45AM +0200, Neil Armstrong wrote:
> Hi,
> 
> On 28/08/2023 10:20, Dmitry Rokosov wrote:
> > On Sun, Aug 27, 2023 at 11:31:35AM +0100, Lucas Tanure wrote:
> > > On 27-08-2023 11:23, Neil Armstrong wrote:
> > > > Hi Lucas,
> > > > 
> > > > Le 27/08/2023 à 12:04, Lucas Tanure a écrit :
> > > > > On 27-08-2023 10:48, Neil Armstrong wrote:
> > > > > > Hi Lucas,
> > > > > > 
> > > > > > Le 27/08/2023 à 10:29, Lucas Tanure a écrit :
> > > > > > > This reverts commit 6a4197f9763325043abf7690a21124a9facbf52e.
> > > > > > > New SoC will use ttyS0 instead of ttyAML, so T7 SoC doesn't
> > > > > > > need a OF_EARLYCON_DECLARE.
> > > > > > > 
> > > > > > > Signed-off-by: Lucas Tanure <tanure@xxxxxxxxx>
> > > > > > > ---
> > > > > > > Since V1:
> > > > > > > - add Signed-off-by:
> > > > > > > 
> > > > > > >    drivers/tty/serial/meson_uart.c | 2 --
> > > > > > >    1 file changed, 2 deletions(-)
> > > > > > > 
> > > > > > > diff --git a/drivers/tty/serial/meson_uart.c
> > > > > > > b/drivers/tty/serial/meson_uart.c
> > > > > > > index c4f61d82fb727..790d910dafa5d 100644
> > > > > > > --- a/drivers/tty/serial/meson_uart.c
> > > > > > > +++ b/drivers/tty/serial/meson_uart.c
> > > > > > > @@ -648,8 +648,6 @@ meson_serial_early_console_setup(struct
> > > > > > > earlycon_device *device, const char *opt
> > > > > > >    OF_EARLYCON_DECLARE(meson, "amlogic,meson-ao-uart",
> > > > > > >                meson_serial_early_console_setup);
> > > > > > > -OF_EARLYCON_DECLARE(meson, "amlogic,t7-uart",
> > > > > > > -            meson_serial_early_console_setup);
> > > > > > >    #define MESON_SERIAL_CONSOLE_PTR(_devname)
> > > > > > > (&meson_serial_console_##_devname)
> > > > > > >    #else
> > > > > > 
> > > > > > How do you use earlycon with this removed ?
> > > > > > 
> > > > > > Neil
> > > > > This is my kernel cmdline:
> > > > > console=ttyS0,921600 no_console_suspend earlycon=ttyS0,0xfe078000
> > > > > 
> > > > > And I can see my log:
> > > > > boot 64bit kernel
> > > > > [    0.000000] Booting Linux on physical CPU 0x0000000000 [0x410fd092]
> > > > > [    0.000000] Linux version 6.5.0-rc7-next-20230825+
> > > > > (tanureal@ryzen) (aarch64-none-linux-gnu-gcc (GNU Toolchain for the
> > > > > A-profile Architecture 10.3-2021.07 (arm-10.29)) 10.3.1 20210621,
> > > > > GNU ld (GNU Toolchain fo3
> > > > > [    0.000000] KASLR disabled due to lack of seed
> > > > > [    0.000000] Machine model: Khadas vim4
> > > > > [    0.000000] OF: reserved mem:
> > > > > 0x0000000005000000..0x00000000052fffff (3072 KiB) nomap non-reusable
> > > > > secmon@5000000
> > > > > [    0.000000] OF: reserved mem:
> > > > > 0x0000000005300000..0x00000000072fffff (32768 KiB) nomap
> > > > > non-reusable secmon@5300000
> > > > > ...
> > > > > [    0.079368] io scheduler mq-deadline registered
> > > > > [    0.079374] io scheduler kyber registered
> > > > > [    0.079549] io scheduler bfq registered
> > > > > [    0.083373] fe078000.serial: ttyS0 at MMIO 0xfe078000 (irq = 14,
> > > > > base_baud = 1500000) is a meson_uart
> > > > > [    0.083403] printk: console [ttyS0] enabled
> > > > > 
> > > > > As the log is OK, and T7 for now is binding against S4 code we
> > > > > should drop this patch and add a S4 one if needed.
> > > > > 
> > > > > But just having this log is not enough for testing earlycon?
> > > > > I am assuming that by just having the log since 0.0000 is a good
> > > > > sign that earlycon is working.
> > > > > Could you give further guidance?
> > > > 
> > > > First the kernel argument is simply "earlycon" with no other options,
> > > > the earlycon code will fetch the first uart using the DT
> > > > /chosen/stdout-path property.
> > > > 
> > > > Then you should see something like right after "Machine model":
> > > > [    0.000000] earlycon: meson0 at MMIO 0x00000000ff803000 (options
> > > > '115200n8')
> > > > 
> > > > The boot log you share doesn't use earlycon, it waits until all
> > > > depedency of the UART
> > > > has been probed before probing the UART driver and prints the whole boot
> > > > log.
> > > > 
> > > > Earlycon is a mechanism to use the UART HW as configured by the
> > > > bootloader in
> > > > a minimal way very early in the boot in order to detect very early lockups.
> > > > 
> > > > Keeping OF_EARLYCON_DECLARE for t7 would enable this.
> > > > 
> > > > Neil
> > > > 
> > > > > 
> > > > > Lucas Tanure
> > > > > 
> > > > 
> > > But then we would need to add Earlycon for S4 too.
> > > How can we add one Earlycon for all future SoCs, like S4 and T7?
> > > 
> > 
> > Per my understanding, you just need to declare UART dts node with the
> > following compatible string: "amlogic,meson-ao-uart". It will enabled
> > earlycon. There is no neccessary to declare separate
> > OF_EARLYCON_DECLARE(). It's working okay for A1 dts:
> 
> This works on A1 because uart_AO_B is an Always-On UART, and using amlogic,meson-ao-uart
> is corrent.
> But for S4 & T7, Amlogic dropped the Always-On power domain, so there's no more AO uarts,
> so using amlogic,meson-ao-uart on those is abusing the DT to enable a driver functionality.
> 
> So the solution is to add those OF_EARLYCON_DECLARE and only use the correct
> /chosen/stdout-path property.

Oh, I didn't know about missing Always-On UART AO power domain. In this
situation I'm fully agree with separate OF_EARLYCON_DECLARE(). Thank you
for explanation!

> > 
> > meson-a1.dtsi uart declaration:
> > 	uart_AO_B: serial@2000 {
> > 		compatible = "amlogic,meson-a1-uart",
> > 			     "amlogic,meson-ao-uart";
> > 		reg = <0x0 0x2000 0x0 0x18>;
> > 		interrupts = <GIC_SPI 26 IRQ_TYPE_EDGE_RISING>;
> > 		clocks = <&xtal>, <&xtal>, <&xtal>;
> > 		clock-names = "xtal", "pclk", "baud";
> > 		status = "disabled";
> > 	};
> > 
> > earlycon declaration from dts:
> > 	aliases {
> > 		serial0 = &uart_AO_B;
> > 	};
> > 
> > 	chosen {
> > 		stdout-path = "serial0:115200n8";
> > 	};
> > 
> > > 
> > > _______________________________________________
> > > linux-amlogic mailing list
> > > linux-amlogic@xxxxxxxxxxxxxxxxxxx
> > > http://lists.infradead.org/mailman/listinfo/linux-amlogic
> > 
> 

-- 
Thank you,
Dmitry