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

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

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@kernel.org>
> Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
> ---
>   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;