[PATCH] acpi: reboot: fix racing after writing to ACPI RESET_REG

[PATCH] acpi: reboot: fix racing after writing to ACPI RESET_REG

[Zhang Rui]

According to the ACPI spec, "The system must reset immediately following
the write to the ACPI RESET_REG register.", but there are cases that the
system does not follow this and results in racing with the subsequetial
reboot mechanism, which brings unexpected behavior.

Fix this by adding a 15ms delay after writing to the ACPI RESET_REG.

Reported-by: Ghorai, Sukumar <sukumar.ghorai@intel.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
---
 drivers/acpi/reboot.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/acpi/reboot.c b/drivers/acpi/reboot.c
index ca707f5b521d..88e6b083d702 100644
--- a/drivers/acpi/reboot.c
+++ b/drivers/acpi/reboot.c
@@ -3,6 +3,7 @@
 #include <linux/pci.h>
 #include <linux/acpi.h>
 #include <acpi/reboot.h>
+#include <linux/delay.h>
 
 #ifdef CONFIG_PCI
 static void acpi_pci_reboot(struct acpi_generic_address *rr, u8 reset_value)
@@ -66,4 +67,10 @@ void acpi_reboot(void)
 		acpi_reset();
 		break;
 	}
+
+	/*
+	 * delay for 15ms in case the system does not shutdown immediately after
+	 * writing to the ACPI reset register
+	 */
+	mdelay(15);
 }
-- 
2.17.1

Re: [PATCH] acpi: reboot: fix racing after writing to ACPI RESET_REG

[Rafael J. Wysocki]

On Sat, Oct 10, 2020 at 4:36 AM Zhang Rui <rui.zhang@intel.com> wrote:
>
> According to the ACPI spec, "The system must reset immediately following
> the write to the ACPI RESET_REG register.", but there are cases that the
> system does not follow this and results in racing with the subsequetial
> reboot mechanism, which brings unexpected behavior.
>
> Fix this by adding a 15ms delay after writing to the ACPI RESET_REG.
>
> Reported-by: Ghorai, Sukumar <sukumar.ghorai@intel.com>
> Signed-off-by: Zhang Rui <rui.zhang@intel.com>
> ---
>  drivers/acpi/reboot.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/drivers/acpi/reboot.c b/drivers/acpi/reboot.c
> index ca707f5b521d..88e6b083d702 100644
> --- a/drivers/acpi/reboot.c
> +++ b/drivers/acpi/reboot.c
> @@ -3,6 +3,7 @@
>  #include <linux/pci.h>
>  #include <linux/acpi.h>
>  #include <acpi/reboot.h>
> +#include <linux/delay.h>
>
>  #ifdef CONFIG_PCI
>  static void acpi_pci_reboot(struct acpi_generic_address *rr, u8 reset_value)
> @@ -66,4 +67,10 @@ void acpi_reboot(void)
>                 acpi_reset();
>                 break;
>         }
> +
> +       /*
> +        * delay for 15ms in case the system does not shutdown immediately after
> +        * writing to the ACPI reset register

It would also be good to make a note of where the 15ms value comes from.

Even if it has been guessed, it will still be good to know that, say,
5 years from now.

> +        */
> +       mdelay(15);
>  }
> --
> 2.17.1
>

Re: [PATCH] acpi: reboot: fix racing after writing to ACPI RESET_REG

[Zhang Rui]

On Mon, 2020-10-12 at 12:42 +0200, Rafael J. Wysocki wrote:
> On Sat, Oct 10, 2020 at 4:36 AM Zhang Rui <rui.zhang@intel.com>
> wrote:
> > 
> > According to the ACPI spec, "The system must reset immediately
> > following
> > the write to the ACPI RESET_REG register.", but there are cases
> > that the
> > system does not follow this and results in racing with the
> > subsequetial
> > reboot mechanism, which brings unexpected behavior.
> > 
> > Fix this by adding a 15ms delay after writing to the ACPI
> > RESET_REG.
> > 
> > Reported-by: Ghorai, Sukumar <sukumar.ghorai@intel.com>
> > Signed-off-by: Zhang Rui <rui.zhang@intel.com>
> > ---
> >  drivers/acpi/reboot.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/drivers/acpi/reboot.c b/drivers/acpi/reboot.c
> > index ca707f5b521d..88e6b083d702 100644
> > --- a/drivers/acpi/reboot.c
> > +++ b/drivers/acpi/reboot.c
> > @@ -3,6 +3,7 @@
> >  #include <linux/pci.h>
> >  #include <linux/acpi.h>
> >  #include <acpi/reboot.h>
> > +#include <linux/delay.h>
> > 
> >  #ifdef CONFIG_PCI
> >  static void acpi_pci_reboot(struct acpi_generic_address *rr, u8
> > reset_value)
> > @@ -66,4 +67,10 @@ void acpi_reboot(void)
> >                 acpi_reset();
> >                 break;
> >         }
> > +
> > +       /*
> > +        * delay for 15ms in case the system does not shutdown
> > immediately after
> > +        * writing to the ACPI reset register
> 
> It would also be good to make a note of where the 15ms value comes
> from.
> 
> Even if it has been guessed, it will still be good to know that, say,
> 5 years from now.
> 
Agreed, patch V2 sent out.

-rui
> > +        */
> > +       mdelay(15);
> >  }
> > --
> > 2.17.1
> >