Re: [PATCH v4 04/14] x86/rtc: replace paravirt rtc check with platform legacy quirk

From: Boris Ostrovsky
Date: Thu Apr 07 2016 - 08:57:58 EST

On 04/06/2016 08:06 PM, Luis R. Rodriguez wrote:
We have 4 types of x86 platforms that disable RTC:

* Intel MID
* Lguest - uses paravirt
* Xen dom-U - uses paravirt
* x86 on legacy systems annotated with an ACPI legacy flag

We can consolidate all of these into a platform specific legacy
quirk set early in boot through i386_start_kernel() and through
x86_64_start_reservations(). This deals with the RTC quirks which
we can rely on through the hardware subarch, the ACPI check can
be dealt with separately.

v2: split the subarch check from the ACPI check, clarify
on the ACPI change commit log why ordering works

Suggested-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxxxx>
---
arch/x86/Makefile | 1 +
arch/x86/include/asm/paravirt.h | 6 ------
arch/x86/include/asm/paravirt_types.h | 5 -----
arch/x86/include/asm/processor.h | 1 -
arch/x86/include/asm/x86_init.h | 13 +++++++++++++
arch/x86/kernel/Makefile | 6 +++++-
arch/x86/kernel/head32.c | 2 ++
arch/x86/kernel/head64.c | 1 +
arch/x86/kernel/platform-quirks.c | 18 ++++++++++++++++++
arch/x86/kernel/rtc.c | 7 ++-----
arch/x86/lguest/boot.c | 1 -
arch/x86/xen/enlighten.c | 3 ---
12 files changed, 42 insertions(+), 22 deletions(-)
create mode 100644 arch/x86/kernel/platform-quirks.c

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 4086abca0b32..f9ed8a7ce2b6 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -209,6 +209,7 @@ endif
head-y := arch/x86/kernel/head_$(BITS).o
head-y += arch/x86/kernel/head$(BITS).o
head-y += arch/x86/kernel/head.o
+head-y += arch/x86/kernel/platform-quirks.o
libs-y += arch/x86/lib/
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 601f1b8f9961..6c7a4a192032 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -20,12 +20,6 @@ static inline int paravirt_enabled(void)
return pv_info.paravirt_enabled;
}
-static inline int paravirt_has_feature(unsigned int feature)
-{
- WARN_ON_ONCE(!pv_info.paravirt_enabled);
- return (pv_info.features & feature);
-}
-
static inline void load_sp0(struct tss_struct *tss,
struct thread_struct *thread)
{
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index e8c2326478c8..6acc1b26cf40 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -70,14 +70,9 @@ struct pv_info {
#endif
int paravirt_enabled;
- unsigned int features; /* valid only if paravirt_enabled is set */
const char *name;
};
-#define paravirt_has(x) paravirt_has_feature(PV_SUPPORTED_##x)
-/* Supported features */
-#define PV_SUPPORTED_RTC (1<<0)
-
struct pv_init_ops {
/*
* Patch may replace one of the defined code sequences with
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 9264476f3d57..0c70c7daa6b8 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -474,7 +474,6 @@ static inline unsigned long current_top_of_stack(void)
#else
#define __cpuid native_cpuid
#define paravirt_enabled() 0
-#define paravirt_has(x) 0
static inline void load_sp0(struct tss_struct *tss,
struct thread_struct *thread)
diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
index 1ae89a2721d6..27d5c3fe5198 100644
--- a/arch/x86/include/asm/x86_init.h
+++ b/arch/x86/include/asm/x86_init.h
@@ -142,6 +142,15 @@ struct x86_cpuinit_ops {
struct timespec;
/**
+ * struct x86_legacy_features - legacy x86 features
+ *
+ * @rtc: this device has a CMOS real-time clock present
+ */
+struct x86_legacy_features {
+ int rtc;
+};
+
+/**
* struct x86_platform_ops - platform specific runtime functions
* @calibrate_tsc: calibrate TSC
* @get_wallclock: get time from HW clock like RTC etc.
@@ -152,6 +161,7 @@ struct timespec;
* @save_sched_clock_state: save state for sched_clock() on suspend
* @restore_sched_clock_state: restore state for sched_clock() on resume
* @apic_post_init: adjust apic if neeeded
+ * @legacy: legacy features
*/
struct x86_platform_ops {
unsigned long (*calibrate_tsc)(void);
@@ -165,6 +175,7 @@ struct x86_platform_ops {
void (*save_sched_clock_state)(void);
void (*restore_sched_clock_state)(void);
void (*apic_post_init)(void);
+ struct x86_legacy_features legacy;
};
struct pci_dev;
@@ -186,6 +197,8 @@ extern struct x86_cpuinit_ops x86_cpuinit;
extern struct x86_platform_ops x86_platform;
extern struct x86_msi_ops x86_msi;
extern struct x86_io_apic_ops x86_io_apic_ops;
+
+extern void x86_early_init_platform_quirks(void);
extern void x86_init_noop(void);
extern void x86_init_uint_noop(unsigned int unused);
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 89f8ade0bc7c..7a9e44d935de 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -2,7 +2,11 @@
# Makefile for the linux kernel.
#
-extra-y := head_$(BITS).o head$(BITS).o head.o vmlinux.lds
+extra-y := head_$(BITS).o
+extra-y += head$(BITS).o
+extra-y += head.o
+extra-y += platform-quirks.o
+extra-y += vmlinux.lds
CPPFLAGS_vmlinux.lds += -U$(UTS_MACHINE)
diff --git a/arch/x86/kernel/head32.c b/arch/x86/kernel/head32.c
index 2911ef3a9f1c..d784bb547a9d 100644
--- a/arch/x86/kernel/head32.c
+++ b/arch/x86/kernel/head32.c
@@ -34,6 +34,8 @@ asmlinkage __visible void __init i386_start_kernel(void)
cr4_init_shadow();
sanitize_boot_params(&boot_params);
+ x86_early_init_platform_quirks();
+
/* Call the subarch specific early setup function */
switch (boot_params.hdr.hardware_subarch) {
case X86_SUBARCH_INTEL_MID:
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 1f4422d5c8d0..b72fb0b71dd1 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -182,6 +182,7 @@ void __init x86_64_start_reservations(char *real_mode_data)
if (!boot_params.hdr.version)
copy_bootdata(__va(real_mode_data));
+ x86_early_init_platform_quirks();
reserve_ebda_region();
switch (boot_params.hdr.hardware_subarch) {
diff --git a/arch/x86/kernel/platform-quirks.c b/arch/x86/kernel/platform-quirks.c
new file mode 100644
index 000000000000..1b114ac5996f
--- /dev/null
+++ b/arch/x86/kernel/platform-quirks.c
@@ -0,0 +1,18 @@
+#include <linux/kernel.h>
+#include <linux/init.h>
+
+#include <asm/setup.h>
+#include <asm/bios_ebda.h>
+
+void __init x86_early_init_platform_quirks(void)
+{
+ x86_platform.legacy.rtc = 1;
+
+ switch (boot_params.hdr.hardware_subarch) {
+ case X86_SUBARCH_XEN:
+ case X86_SUBARCH_LGUEST:
+ case X86_SUBARCH_INTEL_MID:
+ x86_platform.legacy.rtc = 0;
+ break;
+ }
+}

What about Xen dom0 (aka initial domain)?

-boris

--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1192,7 +1192,6 @@ static const struct pv_info xen_info __initconst = {
#ifdef CONFIG_X86_64
.extra_user_64bit_cs = FLAT_USER_CS64,
#endif
- .features = 0,
.name = "Xen",
};
@@ -1525,8 +1524,6 @@ asmlinkage __visible void __init xen_start_kernel(void)
/* Install Xen paravirt ops */
pv_info = xen_info;
- if (xen_initial_domain())
- pv_info.features |= PV_SUPPORTED_RTC;
pv_init_ops = xen_init_ops;
if (!xen_pvh_domain()) {
pv_cpu_ops = xen_cpu_ops;