Messages in this thread | | | Subject | Re: [PATCH 0/2] acpi, x86: Add SPCR table support | From | Jeffrey Hugo <> | Date | Fri, 8 Dec 2017 08:31:53 -0700 |
| |
On 12/8/2017 7:29 AM, Prarit Bhargava wrote: > > > On 12/08/2017 01:29 AM, Ingo Molnar wrote: >> >> * Prarit Bhargava <prarit@redhat.com> 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.
| |