On 12/8/2017 7:29 AM, Prarit Bhargava wrote:
On 12/08/2017 01:29 AM, Ingo Molnar wrote:
* Prarit Bhargava <prarit@xxxxxxxxxx> wrote:
The SPCR (Serial Port Console Redirection) Table provides information
about the configuration of serial port. This information can be used
to configure the early console.
s/about the configuration of serial port
/about the configuration of the serial port
SPCR support was added for arm64 and is made available across all arches
in this patchset. The first patch adds a weak per-arch configuration function
and moves the SPCR code into ACPI. The second patch adds support to x86.
The existing behaviour on arm64 is maintained. If the SPCR exists the
earlycon and console are automatically configured.
s/arm64
/ARM64
which is easier to read and it's also the prevalent spelling:
triton:~/tip> for N in $(git grep -ih arm64 arch/arm64/ | sed 's/[[:punct:]]/ /g'); do echo $N | grep -iw arm64; done | sort | uniq -c
412 arm64
1 Arm64
854 ARM64
The existing default behaviour on x86 is also maintained. If no console or
earlycon parameter is defined and the SPCR exists , the serial port is not
configured. If the earlycon parameter is used both the early console
and the console are configured using the data from the SPCR.
s/exists , the
/exists, the
But, the logic to not use the SPCR looks confusing to me.
The SPCR is only present if the user has explicitly configured a serial console
for that machine, either in the firmware, or remotely via IPMI, correct? I.e. SPCR
will not be spuriously present by default on systems that have a serial console
but the user never expressed any interest for them, right?
If I disable "Serial Port Console Debug" in my BIOS I still see the SPCR configured:
[root@prarit-lab ~]# dmesg | grep SPCR
[ 0.000000] ACPI: SPCR 0x0000000069031000 000050 (v01
00000000 00000000)
AFAICT the SPCR is always enabled on some systems.
"Serial Port Console Debug" sounds like DBG2 to me, although I am unsure
of the specific platform you are referencing.
If so then we should pick up that serial console configuration and activate it,
regardless of any kernel boot options!
I'm worried about someone who doesn't want a console on ttyS0 suddenly ending up
with one. The SPCR could contain incorrect data, etc.
I originally wanted this on by default, but the chances of breaking someone's
setup seems significant doesn't it? Maybe I'm being too cautious. Anyone else
want to weigh in? I'm not ignoring your idea Ingo, I'm just worried about being
yelled at by a user :) because I broke their default console setup.
SPCR is always present on QDF2400 (ARM64 platform). Firmware will
automatically update the SPCR table to point to the correct console (IE
Serial-over-LAN or SOL if configured via IPMI). Unless a user
specifically chooses to override the SPCR via "console=", we expect that
a console will be present based on the data in SPCR.
--
Jeffrey Hugo
Qualcomm Datacenter Technologies as an affiliate of Qualcomm
Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.
--
To unsubscribe from this list: send the line "unsubscribe linux-acpi" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
