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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Wed, 22 Jun 2022 11:03:03 +0200
Message-ID: <CAMuHMdWjzH6GGkaZ_5cjeC6stc80u9Ly+5rrBuk8rKMvM7==8w@mail.gmail.com>
Subject: Re: [PATCH printk v5 1/1] printk: extend console_lock for per-console locking
To:     John Ogness <john.ogness@linutronix.de>
Cc:     Petr Mladek <pmladek@suse.com>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-riscv <linux-riscv@lists.infradead.org>
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Hi John,

On Tue, Apr 26, 2022 at 10:50 AM John Ogness <john.ogness@linutronix.de> wrote:
> Currently threaded console printers synchronize against each
> other using console_lock(). However, different console drivers
> are unrelated and do not require any synchronization between
> each other. Removing the synchronization between the threaded
> console printers will allow each console to print at its own
> speed.

[...]

> Signed-off-by: John Ogness <john.ogness@linutronix.de>

Thanks for your patch, which is now commit 8e274732115f63c1
("printk: extend console_lock for per-console locking") in
v5.19-rc1.

I have bisected another intriguing issue to this commit: on SiPEED
MAiX BiT (Canaan K210 riscv), it no longer prints the line detecting
ttySIF0, i.e. the console output changes like:

     spi-nor spi1.0: gd25lq128d (16384 Kbytes)
     i2c_dev: i2c /dev entries driver
     k210-fpioa 502b0000.pinmux: K210 FPIOA pin controller
    -38000000.serial: ttySIF0 at MMIO 0x38000000 (irq = 1, base_baud =
115200) is a SiFive UART v0
     printk: console [ttySIF0] enabled
     printk: bootconsole [sifive0] disabled
     printk: console [ttySIF0] printing thread started

As this patch does not make any changes to drivers/tty/, and ttySIF0
does work (it's the console), I looked in /proc/kmsg, and bingo,
the missing line is there, so it is generated, but never printed.

I tried taking the port spinlock in sifive_serial_startup(), as
suggested for the meson driver, but that doesn't make a difference.

Do you have a clue?
Thanks!

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds