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")
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 rewrite it based on you, any comments will welcome.
/* If APIC is not integrated, check if SMP configuration is
* found from MP table. If not too, no 82489DX. switch to
* PIC mode
*
* Else APIC is integrated, check if the BIOS allows local APIC
*
*/
if (!lapic_is_integrated()) {
if (!smp_found_config) {
disable_apic = 1;
return APIC_PIC;
}
} else if(!boot_cpu_has(X86_FEATURE_APIC)) {
disable_apic = 1;
pr_info("APIC disabled by BIOS\n");
return APIC_PIC;
}
}
BTW, As the macro APIC_INTEGRATED(x) has already wrapped by
CONFIG_X86_32, I will cleanup the lapic_is_integrated() for readablity
like that:
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 7834f73..63b3ae9 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -211,11 +211,7 @@ static inline int lapic_get_version(void)
*/
static inline int lapic_is_integrated(void)
{
-#ifdef CONFIG_X86_64
- return 1;
-#else
return APIC_INTEGRATED(lapic_get_version());
-#endif
}
Do you think so. ;-)
Thanks,
dou.
~~~~ Now, I haven't think of why smp_found_config has to be
checked here.
In this way, we don't need the CONFIG_X86_64 checking since it's
contained in lapic_is_integrated() already. And the checking is obvious
for understanding. Just not very sure if the checking is adequate.
Just my personal opinion.
+ /* Check BIOS */
+#ifdef CONFIG_X86_64
+ /* On 64-bit, the APIC must be integrated, Check local APIC only */
+ if (!boot_cpu_has(X86_FEATURE_APIC)) {
+ disable_apic = 1;
+ pr_info("APIC disabled by BIOS\n");
+ return APIC_PIC;
+ }
+#else
+ /*
+ * On 32-bit, check whether there is a separate chip or integrated
+ * APIC
+ */
+
+ /* Has a separate chip ? */
+ if (!boot_cpu_has(X86_FEATURE_APIC) && !smp_found_config) {
+ disable_apic = 1;
+
+ return APIC_PIC;
+ }
+
+ /* Has a local APIC ? */
+ if (!boot_cpu_has(X86_FEATURE_APIC) &&
+ APIC_INTEGRATED(boot_cpu_apic_version)) {
+ disable_apic = 1;
+ pr_err(FW_BUG "Local APIC %d not detected, force emulation\n",
+ boot_cpu_physical_apicid);
+
+ return APIC_PIC;
+ }
+#endif
+
+ /* Check MP table or ACPI MADT configuration */
+ if (!smp_found_config) {
+ disable_ioapic_support();
+
+ if (!acpi_lapic)
+ pr_info("APIC: ACPI MADT or MP tables are not
detected\n");
+
+ return APIC_VIRTUAL_WIRE;
+ }
+
+ return APIC_SYMMETRIC_IO;
+}
+
/*
* An initial setup of the virtual wire mode.
*/
--
2.5.5
