On Thu, Jun 8, 2023 at 11:14 AM James Liu <james.liu@xxxxxxx> wrote: > > On Wed, Jun 07, 2023 at 01:19:42PM +0200, Rafael J. Wysocki wrote: > > On Wed, Jun 7, 2023 at 5:44 AM James Liu <james.liu@xxxxxxx> wrote: > > > > > > For AMD Milan platforms, the delay of 15ms is insufficient to avoid racing > > > of reboot mechanisms. That said, the AMD Milan processors don't reboot > > > in 15ms after invoking acpi_reset(). > > > > > > The proposed 50ms delay can effectively work around this issue. > > > This extended delay aligns better with ACPI v6.4 (i.e., sec. 4.8.4.6), > > > which indicates that ideally OSPM should execute spin loops on the CPUs > > > in the system following a write to this register. > > > > > > Signed-off-by: James Liu <james.liu@xxxxxxx> > > > > Why do you want to affect everyone (including guest kernels running in > > virtual machines AFAICS) in order to address a problem specific to one > > platform? > > I hoped to address this issue for any platform requiring a longer delay to > complete ACPI reset in time for any (maybe silicon-level) reasons. Some AMD Milan > platforms were the cases that we've found so far. Do you know about any other? > Except that, since ACPI spec indicates there should be a spin loop (long enough) > after the write instruction to Reset Register, I thought it should be no harms to > the other systems which well consider this spin loop when they claim to support > ACPI reboot. > > Btw, I am just curious, why is the virtual machine mentioned here? The new delay would be over 3 times larger, so some users might be surprised by it at least potentially. > is the 50ms delay in acpi_reboot() for a guest OS on VM so long that some > unexpected behavior might happen? > > > Wouldn't it be better to quirk that platform and document the quirk properly? > > Yeah, it could be. Actually we considered this, and we will consider it again. > > > > --- > > > drivers/acpi/reboot.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/drivers/acpi/reboot.c b/drivers/acpi/reboot.c > > > index b79b7c99c237..002f7c7814a1 100644 > > > --- a/drivers/acpi/reboot.c > > > +++ b/drivers/acpi/reboot.c > > > @@ -78,5 +78,5 @@ void acpi_reboot(void) > > > * The 15ms delay has been found to be long enough for the system > > > * to reboot on the affected platforms. > > > */ > > > - mdelay(15); > > > + mdelay(50); > > > } > > > --
