linux-kernel - Why linux console designed to work in polling mode?

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Message-ID: <CAKZGPAO_Y9+EbeWxNbz==mWhG0fCmwui6p8YkE7YpU4A3PbF8A@mail.gmail.com>
Date:	Wed, 22 Jul 2015 11:57:25 +0530
From:	Arun KS <arunks.linux@...il.com>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:	alexhoppus111@...il.com, Arun KS <getarunks@...il.com>
Subject: Why linux console designed to work in polling mode?

forwarding email to LKML.
Please enlighten on this question. Googling doesn't helped so far.

Thanks,
Arun

From: Alexander <alexhoppus111@...il.com>
Date: Sat, Jul 18, 2015 at 11:23 AM
Subject: Delegating printk work to UART interrupt
To: kernelnewbies@...nelnewbies.org

Hi!
When i checked how kernel printing works, i mentioned that it takes
messages from log_buffer in console_unlock and gives it to
call_console_drivers -> ...-> some uart bsp function. Basically, as i
see this BSP realization tries to flush all message chars in busyloop
... so it waits until FIFO_NOT_FULL bit will be dropped by UART and it
will be able to push the next byte. Basically, as i see userspace
printing do something different. It puts N_FIFO_BYTES and exits, next,
when FIFO will be freed - interrupt will be generated, and other
characters will be put into UART FIFO.
Can we do something similar for kernel printing? i.e. do not busyloop
sending char after char, but put N_FIFO chars and flush  other in
interrupt. When panic will occur we can do busyloop printing again. Is
it reliable? Suppose we have several cores.

Thank you.

--
Alexander <alexhoppus111@...il.com>

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