Message-ID: <23bfd7bc-98ea-42c4-b2d4-6060df5e7080@linaro.org>
Date:   Mon, 28 Aug 2023 10:50:27 +0200
From:   Neil Armstrong <neil.armstrong@...aro.org>
To:     tanure@...ux.com, Dmitry Rokosov <ddrokosov@...rdevices.ru>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Kevin Hilman <khilman@...libre.com>,
        linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org
Subject: Re: [PATCH v2] Revert "tty: serial: meson: Add a earlycon for the T7
 SoC"

On 28/08/2023 10:47, Lucas Tanure wrote:
> On Mon, Aug 28, 2023 at 9:46 AM Dmitry Rokosov <ddrokosov@...rdevices.ru> wrote:
>>
>> 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@...ux.com>
>>>>>>>>> ---
>>>>>>>>> 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@...en) (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@...0000
>>>>>>> [    0.000000] OF: reserved mem:
>>>>>>> 0x0000000005300000..0x00000000072fffff (32768 KiB) nomap
>>>>>>> non-reusable secmon@...0000
>>>>>>> ...
>>>>>>> [    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@...0 {
>>>>              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@...ts.infradead.org
>>>>> http://lists.infradead.org/mailman/listinfo/linux-amlogic
>>>>
>>>
>>
>> --
>> Thank you,
>> Dmitry
> So let's add:
> 
> OF_EARLYCON_DECLARE(meson, "amlogic,meson-s4-uart",
> meson_serial_early_console_setup);
> 
> ok?


Yes

Neil

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