x86/of: Add support for interrupt mode config for x86 OF systems

Hi All,

This patch series mainly adds a boot time interrupt delivery mode configuration option for OF based x86 platforms. Presently, boot time interrupt delivery mode is hardcoded to legacy PIC mode with no option to configure it to virtual wire mode. This patch series aims to extend it by introducing a new optional boolean property for lapic devicetree node which can be used to configure it to virtual wire mode where applicable. Please find below detailed rationale behind it.

Rationale:

References [1], [2] & [6]

For SMP systems, Intel defines three (logically four) interrupt modes during boot/init time while BIOS/bootloader boots & switches to linux kernel.

1. PIC mode - Legacy 8259 PIC interrupt controller.
2. Virtual wire mode via Local APIC - uses local APIC as virtual wire
3. Virtual wire mode via I/O APIC - uses I/O APIC as virtual wire
4. Symmetric I/O mode - final one used by linux for SMP systems.

BIOS/bootloaders are supposed to boot in either #1 or #2 or #3 and then switch to #4 in linux for SMP systems.

For our platform, we use #2.

Detection of which interrupt mode the system is booting in is made by using below global variable in apic.c

int pic_mode __ro_after_init;

Here pic_mode = 1 means #1 (PIC mode) above.
And pic_mode = 0 means #2 or #3 (basically virtual wire mode via apic).

And apic.c while doing setup_local_APIC() uses below code [3]:

        value = apic_read(APIC_LVT0) & APIC_LVT_MASKED;
        if (!cpu && (pic_mode || !value || skip_ioapic_setup)) {
                value = APIC_DM_EXTINT;
                apic_printk(APIC_VERBOSE, "enabled ExtINT on CPU#%d\n", cpu);
        } else {
                value = APIC_DM_EXTINT | APIC_LVT_MASKED;
                apic_printk(APIC_VERBOSE, "masked ExtINT on CPU#%d\n", cpu);
        }
        apic_write(APIC_LVT0, value);

What i understand from above is that if at this point of time, as long as it is cpu0 & pic_mode=1, it will set delivery mode to ExtINT (causes the processor to respond to the interrupt as if the interrupt originated in an externally connected (8259A-compatible) interrupt controller) and enables/ unmask the interrupts. This causes kernel boot crash for platforms which does not support 8259 compatible external PIC.

pic_mode is presently set/populated/initialized at only two places:
1. In mpparse.c [4]
2. In devicetree.c [7]

For #1 MPPARSE Kconfig definition is as below:

config X86_MPPARSE
bool "Enable MPS table" if ACPI
default y
depends on X86_LOCAL_APIC
help
For old smp systems that do not have proper acpi support. Newer systems (esp with 64bit cpus) with acpi support, MADT and DSDT will override it

As seen above, if ACPI is not enabled, then mpparse by default is always enabled. Presently, there is no way to disable MPPARSE (if ACPI is not enabled). This to me appears to be a bug which needs fixing. As per theory, MPPARSE was to support MPS spec [1] as a temporary solution to support SMP systems until a final ACPI standard was added. But now if ACPI is not enabled, it will rely on MPPARSE driver to read MP floating pointer structure's IMCRP Bit 7 of MP feature info byte 2 [5] to figure out if it supports PIC mode or virtual wire mode and initialize pic_mode variable accordingly. If ACPI is enabled, the ACPI code overrides it by using the MADT table spec'ed in ACPI spec [2].

For #2 devicetree.c presently hardcodes pic_mode = 1 (PIC Mode). There is no support to configure virtual wire mode via devicetree path for OF based systems.

Now we have a platform which is OF based & does not use legacy 8259 PIC interrupt controller. Non ACPI compliant as well as non MPPARSE compliant.

For such platforms, it appears to me that hardcoding pic_mode = 1 (PIC Mode) and giving no other choice to choose virtual wire mode is a lacking feature.

Just like mpparse relies on IMCRP bit 7 of MP feature info byte2 [5] to select pic_mode to PIC mode or virtual wire mode. arch/x86/kernel/devicetree.c should also provide some similar configurability to choose interrupt delivery mode & not hardcode it to PIC mode.

This patch is to add above mentioned interrupt mode configurability in x86/of controlled via a new optional bool property.

Please let me know if you find any mistake in above understanding or if you have a alternative better suggestion to solve it or if you find anything odd here in our platform/system. TIA.

The patch is baselined on below git tree (linux-v6.1.0-rc6):
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

[1] https://pdos.csail.mit.edu/6.828/2008/readings/ia32/MPspec.pdf
[2] https://uefi.org/sites/default/files/resources/ACPI_6_3_final_Jan30.pdf
[3] https://elixir.bootlin.com/linux/v6.1-rc5/source/arch/x86/kernel/apic/apic.c#L1691
[4] https://elixir.bootlin.com/linux/v6.1-rc5/source/arch/x86/kernel/mpparse.c#L517
[5] https://www.manualslib.com/manual/77733/Intel-Multiprocessor.html?page=40#manual
[6] https://www.intel.com/content/www/us/en/developer/articles/technical/intel-sdm.html
[7] https://elixir.bootlin.com/linux/v6.1-rc5/source/arch/x86/kernel/devicetree.c#L170

v5:
- Fix make dt_binding_check error.
- Address review concerns from Rob Herring
* Add interrupt-controller & #interrupt-cells properties in lapic binding schema.
* Fix some indentation issues.
- Add Reviewed-by tag from Andy for patch 4/4.

v4:
- Address review concerns from Andy Shevchenko
* Update maintainers in binding files.
* Place URL in YAML schema properly as reference.
* Remove some unnecessary comments from YAML description.
* Remove fixes tag & not treat it as a bug. Treat it as new feature addition instead.
* Use proper prefixes for bindings file (dt-bindings: x86: ioapic:)
* Add Reviewed-by tag from Andy for patch 3/4.

v3:
- Address review concerns from Andy Shevchenko
* Reshuffle patch series changes to make it more logical.
* Patch 1 just converts existing intel,ce4100-ioapic.txt into YAML schema and separates out ioapic & lapic.
* Patch 2 adds new optional property for lapic.
* Patch 3 replaces older printk(KERN_LVL) to newer pr_lvl()
* Patch 4 adds code changes in devicetree.c to support newly added property.
- Fix 'make DT_CHECKER_FLAGS=-m dt_binding_check' errors reported by Rob Herring's bot.

v2:
- Address review concern from Andy - rename property name to make it a bit more positive & self explanatory.
- Found that the bindings document for these HW's (APIC) are a bit off/obsolete and still in text format. Created new YAML schemas one for each - lapic & ioapic. Updated these schemas with latest info and add in new optional property details in the updated schema for lapic. Delete/let go of the text binding doc.
- CC [email protected] as these changes appear to be mainly targeted for devicetree maintainers review & approval.
- Increase CCed list to include all possible people who touched and were involved this part of code/feature addition.

v1:
- Initial draft

Rahul Tanwar (4):
dt-bindings: x86: apic: Convert Intel's APIC bindings to YAML schema
dt-bindings: x86: apic: Introduce new optional bool property for lapic x86/of: Replace printk(KERN_LVL) with pr_lvl()
x86/of: Add support for boot time interrupt delivery mode
configuration

 .../intel,ce4100-ioapic.txt                   | 26 -------
 .../intel,ce4100-ioapic.yaml                  | 60 ++++++++++++++++
 .../intel,ce4100-lapic.yaml                   | 71 +++++++++++++++++++
 arch/x86/kernel/devicetree.c                  | 13 +++-
 4 files changed, 141 insertions(+), 29 deletions(-)
 delete mode 100644 Documentation/devicetree/bindings/interrupt-controller/intel,ce4100-ioapic.txt
 create mode 100644 Documentation/devicetree/bindings/interrupt-controller/intel,ce4100-ioapic.yaml
 create mode 100644 Documentation/devicetree/bindings/interrupt-controller/intel,ce4100-lapic.yaml

2.17.1

Intel's APIC family of interrupt controllers support local APIC (lapic) & I/O APIC (ioapic). Convert existing bindings for lapic & ioapic from text to YAML schema. Separate lapic & ioapic schemas. Addditionally, add description which was missing in text file and add few more required standard properties which were also missing in text file.

---
 .../intel,ce4100-ioapic.txt                   | 26 --------
 .../intel,ce4100-ioapic.yaml                  | 60 +++++++++++++++++++
 .../intel,ce4100-lapic.yaml                   | 57 ++++++++++++++++++
 3 files changed, 117 insertions(+), 26 deletions(-)
 delete mode 100644 Documentation/devicetree/bindings/interrupt-controller/intel,ce4100-ioapic.txt
 create mode 100644 Documentation/devicetree/bindings/interrupt-controller/intel,ce4100-ioapic.yaml
 create mode 100644 Documentation/devicetree/bindings/interrupt-controller/intel,ce4100-lapic.yaml

deleted file mode 100644
index 7d19f494f19a..000000000000
@@ -1,26 +0,0 @@
-Interrupt chips
----------------
-
-* Intel I/O Advanced Programmable Interrupt Controller (IO APIC)
-
-  Required properties:
-  --------------------
-     compatible = "intel,ce4100-ioapic";
-     #interrupt-cells = <2>;
-
-  Device's interrupt property:
-
-     interrupts = <P S>;
-
-  The first number (P) represents the interrupt pin which is wired to the
-  IO APIC. The second number (S) represents the sense of interrupt which
-  should be configured and can be one of:
-    0 - Edge Rising
-    1 - Level Low
-    2 - Level High
-    3 - Edge Falling
-
-* Local APIC
-  Required property:
-
-     compatible = "intel,ce4100-lapic";

2.17.1

Intel defines a few possible interrupt delivery modes. With respect to boot/init time, mainly two interrupt delivery modes are possible. PIC Mode - Legacy external 8259 compliant PIC interrupt controller. Virtual Wire Mode - use lapic as virtual wire interrupt delivery mode.

For ACPI or MPS spec compliant systems, it is figured out by some read only bit field/s available in their respective defined data structures. But for OF based systems, it is by default set to PIC mode. Presently, it is hardcoded to legacy PIC mode for OF based x86 systems with no option to choose the configuration between PIC mode & virtual wire mode.

For this purpose, introduce a new boolean property for interrupt controller node of lapic which can allow it to be configured to virtual wire mode as well.

Property name: 'intel,virtual-wire-mode'
Type: Boolean

If not present/not defined, interrupt delivery mode defaults to legacy PIC mode. If present/defined, interrupt delivery mode is set to virtual wire mode.

---
 .../interrupt-controller/intel,ce4100-lapic.yaml   | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

index 55184cb49432..d2d0145cb889 100644
@@ -39,6 +39,19 @@ properties:
   '#interrupt-cells':
     const: 2
 
+  intel,virtual-wire-mode:
+    description: Intel defines a few possible interrupt delivery
+      modes. With respect to boot/init time, mainly two interrupt
+      delivery modes are possible.
+      PIC Mode - Legacy external 8259 compliant PIC interrupt controller.
+      Virtual Wire Mode - use lapic as virtual wire interrupt delivery mode.
+      For ACPI or MPS spec compliant systems, it is figured out by some read
+      only bit field/s available in their respective defined data structures.
+      For OF based systems, it is by default set to PIC mode.
+      But if this optional boolean property is set, then the interrupt delivery
+      mode is configured to virtual wire compatibility mode.
+    type: boolean
+
 required:
   - compatible
   - reg

@@ -54,4 +67,5 @@ examples:
         reg = <0xfee00000 0x1000>;
         interrupt-controller;
         #interrupt-cells = <2>;
+        intel,virtual-wire-mode;
     };

2.17.1

Use latest available pr_lvl() instead of older printk(KERN_LVL) Just a upgrade of print utilities usage no functional changes.

---
 arch/x86/kernel/devicetree.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index 5cd51f25f446..fcc6f1b7818f 100644
@@ -248,7 +248,7 @@ static void __init dtb_add_ioapic(struct device_node *dn)
 
 	ret = of_address_to_resource(dn, 0, &r);
 	if (ret) {
-		printk(KERN_ERR "Can't obtain address from device node %pOF.\n", dn);
+		pr_err("Can't obtain address from device node %pOF.\n", dn);
 		return;
 	}
 	mp_register_ioapic(++ioapic_id, r.start, gsi_top, &cfg);

@@ -265,7 +265,7 @@ static void __init dtb_ioapic_setup(void)
 		of_ioapic = 1;
 		return;
 	}
-	printk(KERN_ERR "Error: No information about IO-APIC in OF.\n");
+	pr_err("Error: No information about IO-APIC in OF.\n");
 }
 #else
 static void __init dtb_ioapic_setup(void) {}

2.17.1

Presently, init/boot time interrupt delivery mode is enumerated only for ACPI enabled systems by parsing MADT table or for older systems by parsing MP table. But for OF based x86 systems, it is assumed & hardcoded to legacy PIC mode. This causes boot time crash for platforms which do not use 8259 compliant legacy PIC.

Add support for configuration of init time interrupt delivery mode for x86 OF based systems by introducing a new optional boolean property 'intel,virtual-wire-mode' for interrupt-controller node of local APIC. This property emulates IMCRP Bit 7 of MP feature info byte 2 of MP floating pointer structure.

Defaults to legacy PIC mode if absent. Configures it to virtual wire compatibility mode if present.

---
 arch/x86/kernel/devicetree.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

index fcc6f1b7818f..458e43490414 100644
@@ -167,7 +167,14 @@ static void __init dtb_lapic_setup(void)
 			return;
 	}
 	smp_found_config = 1;
-	pic_mode = 1;
+	if (of_property_read_bool(dn, "intel,virtual-wire-mode")) {
+		pr_info("Virtual Wire compatibility mode.\n");
+		pic_mode = 0;
+	} else {
+		pr_info("IMCR and PIC compatibility mode.\n");
+		pic_mode = 1;
+	}
+
 	register_lapic_address(lapic_addr);
 }
 

2.17.1