Messages in this thread | | | From | John Ogness <> | Subject | Re: [PATCH printk v5 1/1] printk: extend console_lock for per-console locking | Date | Thu, 23 Jun 2022 00:43:15 +0206 |
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On 2022-06-22, Geert Uytterhoeven <geert@linux-m68k.org> wrote: > 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.
What is sifive0? Are you using the earlycon driver to create an early boot console? Can I see your boot args?
There is a known issue the that earlycon does not synchronize with normal consoles. A patch was recently posted [0] on LKML.
> I tried taking the port spinlock in sifive_serial_startup(), as > suggested for the meson driver, but that doesn't make a difference.
It may not have made a difference for you, but it should be there. sifive_serial_startup() is writing to SIFIVE_SERIAL_IE_OFFS without taking port->lock. sifive_serial_console_write() also writes to this register (under port->lock). This could lead to RX watermark interrupts being disabled for some time. The problem is not as bad as it was with the meson driver because __ssp_enable_rxwm() is updating the shadow copy. But still, it is a bug. And anyway we shouldn't have 2 CPUs writing to a register simultaneously.
John Ogness
[0] https://lore.kernel.org/lkml/20220621090900.GB7891@pathway.suse.cz
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