Hi Baoquan,
At 09/07/2017 01:22 PM, Baoquan He wrote:
On 09/07/17 at 12:19pm, Dou Liyang wrote:
Hi Baoquan
I am wordy one ah:
our target is checking if BIOS supports APIC, no matter what
type(separated/integrated) it is. if not, go to PIC mode.
Let‘s discuss the original logic and the smp_found_config,
then take about your code.
The existing logic is:
if (!boot_cpu_has(X86_FEATURE_APIC) && !smp_found_config) ...(1)
return -1;
if (!boot_cpu_has(X86_FEATURE_APIC) &&
APIC_INTEGRATED(boot_cpu_apic_version)) { ...(2)
pr_err(....);
why smp_found_config has to be checked in (1)?
Because, In case of discrete (pretty old) apics we may not set
X86_FEATURE_APIC bit in cpuid, with 82489DX we can't rely on apic
feature bit retrieved via cpuid(boot_cpu_has(X86_FEATURE_APIC)).[1]
So we assume that if SMP configuration is found from MP table
(smp_found_config = 1) in above case, there maybe a separated
chip in our pc.
After passing the check of (1), we in (2), check whether local APIC
is detected or not, If we have a BIOS bug.
[1] Commit 8312136fa8b0("x86, apic: Fix missed handling of discrete apics")
Hmm, sounds reasonable. Just a sentence to describe it could be better.
OK, I will
At 09/06/2017 06:17 PM, Baoquan He wrote:
Hi Dou,
On 08/28/17 at 11:20am, Dou Liyang wrote:
+static int __init apic_intr_mode_select(void)
+{
+ /* Check kernel option */
+ if (disable_apic) {
+ pr_info("APIC disabled via kernel command line\n");
+ return APIC_PIC;
+ }
+
I am not very familiar with cpu registers, not sure if we can adjust
below code flow as:
/* If APIC is integrated, check local APIC only */
if (lapic_is_integrated() && !boot_cpu_has(X86_FEATURE_APIC)) {
disable_apic = 1;
pr_info("APIC disabled by BIOS\n");
return APIC_PIC;
}
/* If APIC is on a separate chip, check if smp_found_config is found*/
if (!lapic_is_integrated() && !smp_found_config) {
disable_apic = 1;
return APIC_PIC;
}
Yes, Awesome, we first consider it from APIC register space, then
the BOIS and software configration. let me do more investigation.
I thought again and again, I would not change this check logic.
Because actually, we have three possibilities:
1. ACPI on chip
2. 82489DX
3. no APIC
lapic_is_integrated() is used to check the APIC's type which is
APIC on chip or 82489DX. It has a prerequisite, we should avoid
the third possibility(no APIC) first, which is decided by
boot_cpu_has(X86_FEATURE_APIC) and smp_found_config. So, the original
logic:
if (!boot_cpu_has(X86_FEATURE_APIC) && !smp_found_config)
...is not just for 82489DX, but also for no APIC.
It looks more correct and understandable than us.
I am sorry my comments were wrong, and misled us. I will modify it
in my next version.
BTW, How about your test result, is this series OK?
Thanks,
dou.
