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

[Zhang Rui <rui.zhang@intel.com>]

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
> >