[stable] x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag

[stable] x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag

[Ben Hutchings]

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Would this be a sensible addition to 3.16-stable or any older stable
branch?

commit 44be28e9dd9880dca3e2cbf7a844f2114e67f2cb
Author: Matt Fleming <matt.fleming@intel.com>
Date:   Fri Jun 13 12:39:55 2014 +0100

    x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag

Ben.

-- 
Ben Hutchings
If you seem to know what you are doing, you'll be given more to do.

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Re: [stable] x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag

[Matt Fleming]

On Mon, 2015-05-04 at 02:33 +0100, Ben Hutchings wrote:
> Would this be a sensible addition to 3.16-stable or any older stable
> branch?
> 
> commit 44be28e9dd9880dca3e2cbf7a844f2114e67f2cb
> Author: Matt Fleming <matt.fleming@intel.com>
> Date:   Fri Jun 13 12:39:55 2014 +0100
> 
>     x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag

I'm not sure what the support for ACPI hardware-reduced platforms (ASUS
T100, etc) is like in the stable releases but if it does exist then yeah
you probably want the above commit. The above commit should be a pretty
low-risk change.

Be sure to also include commit 8562c99cdd30 ("efi/reboot: Add generic
wrapper around EfiResetSystem()") and commit 0c5ed61adbdb ("efi/reboot:
Allow powering off machines using EFI").

Re: [stable] x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag

[Ben Hutchings]

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On Mon, 2015-05-04 at 12:20 +0100, Matt Fleming wrote:
> On Mon, 2015-05-04 at 02:33 +0100, Ben Hutchings wrote:
> > Would this be a sensible addition to 3.16-stable or any older stable
> > branch?
> > 
> > commit 44be28e9dd9880dca3e2cbf7a844f2114e67f2cb
> > Author: Matt Fleming <matt.fleming@intel.com>
> > Date:   Fri Jun 13 12:39:55 2014 +0100
> > 
> >     x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag
> 
> I'm not sure what the support for ACPI hardware-reduced platforms (ASUS
> T100, etc) is like in the stable releases but if it does exist then yeah
> you probably want the above commit. The above commit should be a pretty
> low-risk change.

I understand that the Asus T100 at least is mostly working under 3.16.

> Be sure to also include commit 8562c99cdd30 ("efi/reboot: Add generic
> wrapper around EfiResetSystem()") and commit 0c5ed61adbdb ("efi/reboot:
> Allow powering off machines using EFI").

Thanks.

Ben.

-- 
Ben Hutchings
If you seem to know what you are doing, you'll be given more to do.

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Re: [stable] x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag

[Luis Henriques]

On Mon, May 04, 2015 at 02:34:52PM +0100, Ben Hutchings wrote:
> On Mon, 2015-05-04 at 12:20 +0100, Matt Fleming wrote:
> > On Mon, 2015-05-04 at 02:33 +0100, Ben Hutchings wrote:
> > > Would this be a sensible addition to 3.16-stable or any older stable
> > > branch?
> > > 
> > > commit 44be28e9dd9880dca3e2cbf7a844f2114e67f2cb
> > > Author: Matt Fleming <matt.fleming@intel.com>
> > > Date:   Fri Jun 13 12:39:55 2014 +0100
> > > 
> > >     x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag
> > 
> > I'm not sure what the support for ACPI hardware-reduced platforms (ASUS
> > T100, etc) is like in the stable releases but if it does exist then yeah
> > you probably want the above commit. The above commit should be a pretty
> > low-risk change.
> 
> I understand that the Asus T100 at least is mostly working under 3.16.
> 
> > Be sure to also include commit 8562c99cdd30 ("efi/reboot: Add generic
> > wrapper around EfiResetSystem()") and commit 0c5ed61adbdb ("efi/reboot:
> > Allow powering off machines using EFI").
> 

Thank you Ben and Matt.  I'll have a look at these commits and queue
them for the next release.

Cheers,
--
Lu�s

Re: [stable] x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag

[Luis Henriques]

On Tue, May 05, 2015 at 10:10:04AM +0100, Luis Henriques wrote:
> On Mon, May 04, 2015 at 02:34:52PM +0100, Ben Hutchings wrote:
> > On Mon, 2015-05-04 at 12:20 +0100, Matt Fleming wrote:
> > > On Mon, 2015-05-04 at 02:33 +0100, Ben Hutchings wrote:
> > > > Would this be a sensible addition to 3.16-stable or any older stable
> > > > branch?
> > > > 
> > > > commit 44be28e9dd9880dca3e2cbf7a844f2114e67f2cb
> > > > Author: Matt Fleming <matt.fleming@intel.com>
> > > > Date:   Fri Jun 13 12:39:55 2014 +0100
> > > > 
> > > >     x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag
> > > 
> > > I'm not sure what the support for ACPI hardware-reduced platforms (ASUS
> > > T100, etc) is like in the stable releases but if it does exist then yeah
> > > you probably want the above commit. The above commit should be a pretty
> > > low-risk change.
> > 
> > I understand that the Asus T100 at least is mostly working under 3.16.
> > 
> > > Be sure to also include commit 8562c99cdd30 ("efi/reboot: Add generic
> > > wrapper around EfiResetSystem()") and commit 0c5ed61adbdb ("efi/reboot:
> > > Allow powering off machines using EFI").
> > 

Ok, it looks like the easy approach to bring this into 3.16 is to pick
the following commits (in this order):

  eeb9db09f738 x86/efi: Move all workarounds to a separate file quirks.c
  8562c99cdd30 efi/reboot: Add generic wrapper around EfiResetSystem()
  0c5ed61adbdb efi/reboot: Allow powering off machines using EFI
  44be28e9dd98 x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag

All of these are clean cherry-picks (except for the last one that
needs same really small context adjustment).  If there's no objection,
I'll be sending this out for review shortly.

Cheers,
--
Lu�s

Re: [stable] x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag

[Ben Hutchings]

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On Tue, 2015-05-05 at 15:29 +0100, Luis Henriques wrote:
> On Tue, May 05, 2015 at 10:10:04AM +0100, Luis Henriques wrote:
> > On Mon, May 04, 2015 at 02:34:52PM +0100, Ben Hutchings wrote:
> > > On Mon, 2015-05-04 at 12:20 +0100, Matt Fleming wrote:
> > > > On Mon, 2015-05-04 at 02:33 +0100, Ben Hutchings wrote:
> > > > > Would this be a sensible addition to 3.16-stable or any older stable
> > > > > branch?
> > > > > 
> > > > > commit 44be28e9dd9880dca3e2cbf7a844f2114e67f2cb
> > > > > Author: Matt Fleming <matt.fleming@intel.com>
> > > > > Date:   Fri Jun 13 12:39:55 2014 +0100
> > > > > 
> > > > >     x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag
> > > > 
> > > > I'm not sure what the support for ACPI hardware-reduced platforms (ASUS
> > > > T100, etc) is like in the stable releases but if it does exist then yeah
> > > > you probably want the above commit. The above commit should be a pretty
> > > > low-risk change.
> > > 
> > > I understand that the Asus T100 at least is mostly working under 3.16.
> > > 
> > > > Be sure to also include commit 8562c99cdd30 ("efi/reboot: Add generic
> > > > wrapper around EfiResetSystem()") and commit 0c5ed61adbdb ("efi/reboot:
> > > > Allow powering off machines using EFI").
> > > 
> 
> Ok, it looks like the easy approach to bring this into 3.16 is to pick
> the following commits (in this order):
> 
>   eeb9db09f738 x86/efi: Move all workarounds to a separate file quirks.c
>   8562c99cdd30 efi/reboot: Add generic wrapper around EfiResetSystem()
>   0c5ed61adbdb efi/reboot: Allow powering off machines using EFI
>   44be28e9dd98 x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag
> 
> All of these are clean cherry-picks (except for the last one that
> needs same really small context adjustment).  If there's no objection,
> I'll be sending this out for review shortly.

The first one is really too big according to stable rules.  Sorry I
raised this; I didn't realise there were all these dependencies.

Ben.

-- 
Ben Hutchings
Once a job is fouled up, anything done to improve it makes it worse.

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Re: [stable] x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag

[Luis Henriques]

On Tue, May 05, 2015 at 03:59:59PM +0100, Ben Hutchings wrote:
> On Tue, 2015-05-05 at 15:29 +0100, Luis Henriques wrote:
> > On Tue, May 05, 2015 at 10:10:04AM +0100, Luis Henriques wrote:
> > > On Mon, May 04, 2015 at 02:34:52PM +0100, Ben Hutchings wrote:
> > > > On Mon, 2015-05-04 at 12:20 +0100, Matt Fleming wrote:
> > > > > On Mon, 2015-05-04 at 02:33 +0100, Ben Hutchings wrote:
> > > > > > Would this be a sensible addition to 3.16-stable or any older stable
> > > > > > branch?
> > > > > > 
> > > > > > commit 44be28e9dd9880dca3e2cbf7a844f2114e67f2cb
> > > > > > Author: Matt Fleming <matt.fleming@intel.com>
> > > > > > Date:   Fri Jun 13 12:39:55 2014 +0100
> > > > > > 
> > > > > >     x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag
> > > > > 
> > > > > I'm not sure what the support for ACPI hardware-reduced platforms (ASUS
> > > > > T100, etc) is like in the stable releases but if it does exist then yeah
> > > > > you probably want the above commit. The above commit should be a pretty
> > > > > low-risk change.
> > > > 
> > > > I understand that the Asus T100 at least is mostly working under 3.16.
> > > > 
> > > > > Be sure to also include commit 8562c99cdd30 ("efi/reboot: Add generic
> > > > > wrapper around EfiResetSystem()") and commit 0c5ed61adbdb ("efi/reboot:
> > > > > Allow powering off machines using EFI").
> > > > 
> > 
> > Ok, it looks like the easy approach to bring this into 3.16 is to pick
> > the following commits (in this order):
> > 
> >   eeb9db09f738 x86/efi: Move all workarounds to a separate file quirks.c
> >   8562c99cdd30 efi/reboot: Add generic wrapper around EfiResetSystem()
> >   0c5ed61adbdb efi/reboot: Allow powering off machines using EFI
> >   44be28e9dd98 x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag
> > 
> > All of these are clean cherry-picks (except for the last one that
> > needs same really small context adjustment).  If there's no objection,
> > I'll be sending this out for review shortly.
> 
> The first one is really too big according to stable rules.  Sorry I
> raised this; I didn't realise there were all these dependencies.

True, that commit simply moves code around but it's still huge.

Anyway, a different approach would be to backport 44be28e9dd98 by
moving the changes done to quirks.c into efi.c.  I'm attaching a
(just compile tested) backport bellow.

Obviously, the 2 other commits are still required i.e. we're only
dropping eeb9db09f738 ("x86/efi: Move all workarounds to a separate
file quirks.c").

Cheers,
--
Lu�s

>From 41aaf1bdee7e9423a35aee310703111eef96b6b3 Mon Sep 17 00:00:00 2001
From: Matt Fleming <matt.fleming@intel.com>
Date: Fri, 13 Jun 2014 12:39:55 +0100
Subject: [PATCH] x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced
 flag

commit 44be28e9dd9880dca3e2cbf7a844f2114e67f2cb upstream.

It appears that the BayTrail-T class of hardware requires EFI in order
to powerdown and reboot and no other reliable method exists.

This quirk is generally applicable to all hardware that has the ACPI
Hardware Reduced bit set, since usually ACPI would be the preferred
method.

Cc: Len Brown <len.brown@intel.com>
Cc: Mark Salter <msalter@redhat.com>
Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>
Cc: Ben Hutchings <ben@decadent.org.uk>
[ luis: backported to 3.16:
  - move changes from quirks.c into efi.c
  - adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
---
 arch/x86/include/asm/efi.h    |  7 +++++++
 arch/x86/kernel/reboot.c      | 18 ++++++++++++++++--
 arch/x86/platform/efi/efi.c   | 23 +++++++++++++++++++++++
 drivers/firmware/efi/reboot.c |  8 ++++++++
 include/linux/efi.h           |  1 +
 5 files changed, 55 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index 1eb5f6433ad8..81396a9a9277 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -156,6 +156,9 @@ static inline efi_status_t efi_thunk_set_virtual_address_map(
 	return EFI_SUCCESS;
 }
 #endif /* CONFIG_EFI_MIXED */
+
+extern bool efi_reboot_required(void);
+
 #else
 /*
  * IF EFI is not configured, have the EFI calls return -ENOSYS.
@@ -168,6 +171,10 @@ static inline efi_status_t efi_thunk_set_virtual_address_map(
 #define efi_call5(_f, _a1, _a2, _a3, _a4, _a5)		(-ENOSYS)
 #define efi_call6(_f, _a1, _a2, _a3, _a4, _a5, _a6)	(-ENOSYS)
 static inline void parse_efi_setup(u64 phys_addr, u32 data_len) {}
+static inline bool efi_reboot_required(void)
+{
+	return false;
+}
 #endif /* CONFIG_EFI */
 
 #endif /* _ASM_X86_EFI_H */
diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
index 7c138543c500..587be13be0be 100644
--- a/arch/x86/kernel/reboot.c
+++ b/arch/x86/kernel/reboot.c
@@ -28,6 +28,7 @@
 #include <linux/mc146818rtc.h>
 #include <asm/realmode.h>
 #include <asm/x86_init.h>
+#include <asm/efi.h>
 
 /*
  * Power off function, if any
@@ -411,12 +412,25 @@ static struct dmi_system_id __initdata reboot_dmi_table[] = {
 
 static int __init reboot_init(void)
 {
+	int rv;
+
 	/*
 	 * Only do the DMI check if reboot_type hasn't been overridden
 	 * on the command line
 	 */
-	if (reboot_default)
-		dmi_check_system(reboot_dmi_table);
+	if (!reboot_default)
+		return 0;
+
+	/*
+	 * The DMI quirks table takes precedence. If no quirks entry
+	 * matches and the ACPI Hardware Reduced bit is set, force EFI
+	 * reboot.
+	 */
+	rv = dmi_check_system(reboot_dmi_table);
+
+	if (!rv && efi_reboot_required())
+		reboot_type = BOOT_EFI;
+
 	return 0;
 }
 core_initcall(reboot_init);
diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index 87fc96bcc13c..53a324606d11 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -44,6 +44,7 @@
 #include <linux/io.h>
 #include <linux/reboot.h>
 #include <linux/bcd.h>
+#include <linux/acpi.h>
 
 #include <asm/setup.h>
 #include <asm/efi.h>
@@ -1340,3 +1341,25 @@ void __init efi_apply_memmap_quirks(void)
 	if (is_uv_system())
 		set_bit(EFI_OLD_MEMMAP, &efi.flags);
 }
+
+/*
+ * For most modern platforms the preferred method of powering off is via
+ * ACPI. However, there are some that are known to require the use of
+ * EFI runtime services and for which ACPI does not work at all.
+ *
+ * Using EFI is a last resort, to be used only if no other option
+ * exists.
+ */
+bool efi_reboot_required(void)
+{
+	if (!acpi_gbl_reduced_hardware)
+		return false;
+
+	efi_reboot_quirk_mode = EFI_RESET_WARM;
+	return true;
+}
+
+bool efi_poweroff_required(void)
+{
+	return !!acpi_gbl_reduced_hardware;
+}
diff --git a/drivers/firmware/efi/reboot.c b/drivers/firmware/efi/reboot.c
index e9eeeb3c6345..9c59d1c795d1 100644
--- a/drivers/firmware/efi/reboot.c
+++ b/drivers/firmware/efi/reboot.c
@@ -5,6 +5,8 @@
 #include <linux/efi.h>
 #include <linux/reboot.h>
 
+int efi_reboot_quirk_mode = -1;
+
 void efi_reboot(enum reboot_mode reboot_mode, const char *__unused)
 {
 	int efi_mode;
@@ -22,6 +24,12 @@ void efi_reboot(enum reboot_mode reboot_mode, const char *__unused)
 		break;
 	}
 
+	/*
+	 * If a quirk forced an EFI reset mode, always use that.
+	 */
+	if (efi_reboot_quirk_mode != -1)
+		efi_mode = efi_reboot_quirk_mode;
+
 	efi.reset_system(efi_mode, EFI_SUCCESS, 0, NULL);
 }
 
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 2539aff31808..b3fac7c1656c 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -876,6 +876,7 @@ extern void efi_reserve_boot_services(void);
 extern int efi_get_fdt_params(struct efi_fdt_params *params, int verbose);
 extern struct efi_memory_map memmap;
 
+extern int efi_reboot_quirk_mode;
 extern bool efi_poweroff_required(void);
 
 /* Iterate through an efi_memory_map */

Re: [stable] x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag

[Ben Hutchings]

[-- Attachment #1: Type: text/plain, Size: 8617 bytes --]

On Tue, 2015-05-05 at 16:41 +0100, Luis Henriques wrote:
> On Tue, May 05, 2015 at 03:59:59PM +0100, Ben Hutchings wrote:
> > On Tue, 2015-05-05 at 15:29 +0100, Luis Henriques wrote:
> > > On Tue, May 05, 2015 at 10:10:04AM +0100, Luis Henriques wrote:
> > > > On Mon, May 04, 2015 at 02:34:52PM +0100, Ben Hutchings wrote:
> > > > > On Mon, 2015-05-04 at 12:20 +0100, Matt Fleming wrote:
> > > > > > On Mon, 2015-05-04 at 02:33 +0100, Ben Hutchings wrote:
> > > > > > > Would this be a sensible addition to 3.16-stable or any older stable
> > > > > > > branch?
> > > > > > > 
> > > > > > > commit 44be28e9dd9880dca3e2cbf7a844f2114e67f2cb
> > > > > > > Author: Matt Fleming <matt.fleming@intel.com>
> > > > > > > Date:   Fri Jun 13 12:39:55 2014 +0100
> > > > > > > 
> > > > > > >     x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag
> > > > > > 
> > > > > > I'm not sure what the support for ACPI hardware-reduced platforms (ASUS
> > > > > > T100, etc) is like in the stable releases but if it does exist then yeah
> > > > > > you probably want the above commit. The above commit should be a pretty
> > > > > > low-risk change.
> > > > > 
> > > > > I understand that the Asus T100 at least is mostly working under 3.16.
> > > > > 
> > > > > > Be sure to also include commit 8562c99cdd30 ("efi/reboot: Add generic
> > > > > > wrapper around EfiResetSystem()") and commit 0c5ed61adbdb ("efi/reboot:
> > > > > > Allow powering off machines using EFI").
> > > > > 
> > > 
> > > Ok, it looks like the easy approach to bring this into 3.16 is to pick
> > > the following commits (in this order):
> > > 
> > >   eeb9db09f738 x86/efi: Move all workarounds to a separate file quirks.c
> > >   8562c99cdd30 efi/reboot: Add generic wrapper around EfiResetSystem()
> > >   0c5ed61adbdb efi/reboot: Allow powering off machines using EFI
> > >   44be28e9dd98 x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced flag
> > > 
> > > All of these are clean cherry-picks (except for the last one that
> > > needs same really small context adjustment).  If there's no objection,
> > > I'll be sending this out for review shortly.
> > 
> > The first one is really too big according to stable rules.  Sorry I
> > raised this; I didn't realise there were all these dependencies.
> 
> True, that commit simply moves code around but it's still huge.
> 
> Anyway, a different approach would be to backport 44be28e9dd98 by
> moving the changes done to quirks.c into efi.c.  I'm attaching a
> (just compile tested) backport bellow.
> 
> Obviously, the 2 other commits are still required i.e. we're only
> dropping eeb9db09f738 ("x86/efi: Move all workarounds to a separate
> file quirks.c").

That would be my personal preference.

Ben.

> Cheers,
> --
> Luís
> 
> From 41aaf1bdee7e9423a35aee310703111eef96b6b3 Mon Sep 17 00:00:00 2001
> From: Matt Fleming <matt.fleming@intel.com>
> Date: Fri, 13 Jun 2014 12:39:55 +0100
> Subject: [PATCH] x86/reboot: Add EFI reboot quirk for ACPI Hardware Reduced
>  flag
> 
> commit 44be28e9dd9880dca3e2cbf7a844f2114e67f2cb upstream.
> 
> It appears that the BayTrail-T class of hardware requires EFI in order
> to powerdown and reboot and no other reliable method exists.
> 
> This quirk is generally applicable to all hardware that has the ACPI
> Hardware Reduced bit set, since usually ACPI would be the preferred
> method.
> 
> Cc: Len Brown <len.brown@intel.com>
> Cc: Mark Salter <msalter@redhat.com>
> Cc: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
> Signed-off-by: Matt Fleming <matt.fleming@intel.com>
> Cc: Ben Hutchings <ben@decadent.org.uk>
> [ luis: backported to 3.16:
>   - move changes from quirks.c into efi.c
>   - adjusted context ]
> Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
> ---
>  arch/x86/include/asm/efi.h    |  7 +++++++
>  arch/x86/kernel/reboot.c      | 18 ++++++++++++++++--
>  arch/x86/platform/efi/efi.c   | 23 +++++++++++++++++++++++
>  drivers/firmware/efi/reboot.c |  8 ++++++++
>  include/linux/efi.h           |  1 +
>  5 files changed, 55 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
> index 1eb5f6433ad8..81396a9a9277 100644
> --- a/arch/x86/include/asm/efi.h
> +++ b/arch/x86/include/asm/efi.h
> @@ -156,6 +156,9 @@ static inline efi_status_t efi_thunk_set_virtual_address_map(
>  	return EFI_SUCCESS;
>  }
>  #endif /* CONFIG_EFI_MIXED */
> +
> +extern bool efi_reboot_required(void);
> +
>  #else
>  /*
>   * IF EFI is not configured, have the EFI calls return -ENOSYS.
> @@ -168,6 +171,10 @@ static inline efi_status_t efi_thunk_set_virtual_address_map(
>  #define efi_call5(_f, _a1, _a2, _a3, _a4, _a5)		(-ENOSYS)
>  #define efi_call6(_f, _a1, _a2, _a3, _a4, _a5, _a6)	(-ENOSYS)
>  static inline void parse_efi_setup(u64 phys_addr, u32 data_len) {}
> +static inline bool efi_reboot_required(void)
> +{
> +	return false;
> +}
>  #endif /* CONFIG_EFI */
>  
>  #endif /* _ASM_X86_EFI_H */
> diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
> index 7c138543c500..587be13be0be 100644
> --- a/arch/x86/kernel/reboot.c
> +++ b/arch/x86/kernel/reboot.c
> @@ -28,6 +28,7 @@
>  #include <linux/mc146818rtc.h>
>  #include <asm/realmode.h>
>  #include <asm/x86_init.h>
> +#include <asm/efi.h>
>  
>  /*
>   * Power off function, if any
> @@ -411,12 +412,25 @@ static struct dmi_system_id __initdata reboot_dmi_table[] = {
>  
>  static int __init reboot_init(void)
>  {
> +	int rv;
> +
>  	/*
>  	 * Only do the DMI check if reboot_type hasn't been overridden
>  	 * on the command line
>  	 */
> -	if (reboot_default)
> -		dmi_check_system(reboot_dmi_table);
> +	if (!reboot_default)
> +		return 0;
> +
> +	/*
> +	 * The DMI quirks table takes precedence. If no quirks entry
> +	 * matches and the ACPI Hardware Reduced bit is set, force EFI
> +	 * reboot.
> +	 */
> +	rv = dmi_check_system(reboot_dmi_table);
> +
> +	if (!rv && efi_reboot_required())
> +		reboot_type = BOOT_EFI;
> +
>  	return 0;
>  }
>  core_initcall(reboot_init);
> diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
> index 87fc96bcc13c..53a324606d11 100644
> --- a/arch/x86/platform/efi/efi.c
> +++ b/arch/x86/platform/efi/efi.c
> @@ -44,6 +44,7 @@
>  #include <linux/io.h>
>  #include <linux/reboot.h>
>  #include <linux/bcd.h>
> +#include <linux/acpi.h>
>  
>  #include <asm/setup.h>
>  #include <asm/efi.h>
> @@ -1340,3 +1341,25 @@ void __init efi_apply_memmap_quirks(void)
>  	if (is_uv_system())
>  		set_bit(EFI_OLD_MEMMAP, &efi.flags);
>  }
> +
> +/*
> + * For most modern platforms the preferred method of powering off is via
> + * ACPI. However, there are some that are known to require the use of
> + * EFI runtime services and for which ACPI does not work at all.
> + *
> + * Using EFI is a last resort, to be used only if no other option
> + * exists.
> + */
> +bool efi_reboot_required(void)
> +{
> +	if (!acpi_gbl_reduced_hardware)
> +		return false;
> +
> +	efi_reboot_quirk_mode = EFI_RESET_WARM;
> +	return true;
> +}
> +
> +bool efi_poweroff_required(void)
> +{
> +	return !!acpi_gbl_reduced_hardware;
> +}
> diff --git a/drivers/firmware/efi/reboot.c b/drivers/firmware/efi/reboot.c
> index e9eeeb3c6345..9c59d1c795d1 100644
> --- a/drivers/firmware/efi/reboot.c
> +++ b/drivers/firmware/efi/reboot.c
> @@ -5,6 +5,8 @@
>  #include <linux/efi.h>
>  #include <linux/reboot.h>
>  
> +int efi_reboot_quirk_mode = -1;
> +
>  void efi_reboot(enum reboot_mode reboot_mode, const char *__unused)
>  {
>  	int efi_mode;
> @@ -22,6 +24,12 @@ void efi_reboot(enum reboot_mode reboot_mode, const char *__unused)
>  		break;
>  	}
>  
> +	/*
> +	 * If a quirk forced an EFI reset mode, always use that.
> +	 */
> +	if (efi_reboot_quirk_mode != -1)
> +		efi_mode = efi_reboot_quirk_mode;
> +
>  	efi.reset_system(efi_mode, EFI_SUCCESS, 0, NULL);
>  }
>  
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index 2539aff31808..b3fac7c1656c 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -876,6 +876,7 @@ extern void efi_reserve_boot_services(void);
>  extern int efi_get_fdt_params(struct efi_fdt_params *params, int verbose);
>  extern struct efi_memory_map memmap;
>  
> +extern int efi_reboot_quirk_mode;
>  extern bool efi_poweroff_required(void);
>  
>  /* Iterate through an efi_memory_map */

-- 
Ben Hutchings
Once a job is fouled up, anything done to improve it makes it worse.

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