Re: [edk2][PATCH V1 1/1] ArmPkg: Handle warm reboot request correctly

["Pranav Madhu" <pranav.madhu@arm.com>]

Hi Sami,

Thanks for your comments. Please find my reply inline.

Regards,
Pranav

> -----Original Message-----
> From: Sami Mujawar <Sami.Mujawar@arm.com>
> Sent: Thursday, March 10, 2022 9:01 PM
> To: Pranav Madhu <Pranav.Madhu@arm.com>; devel@edk2.groups.io
> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>; nd <nd@arm.com>
> Subject: Re: [edk2][PATCH V1 1/1] ArmPkg: Handle warm reboot request
> correctly
> 
> Hi Pranav,
> 
> Thank you for this patch.
> 
> Please find my response inline marked [SAMI].
> 
> Regards,
> 
> Sami Mujawar
> 
> 
> On 10/03/2022 01:10 PM, Pranav Madhu wrote:
> > The warm reboot requests are mapped to cold reboot as the power
> > control module was not capable of handling the warm reboot requests in
> > the legacy implementation. The support for warm reboot support is
> > added into the power control module. To support warm reset, update
> > ArmPsciResetSystemLib, and there by invoke the PSCI call with
> > parameters for warm reboot.
> >
> > Signed-off-by: Pranav Madhu <pranav.madhu@arm.com>
> > ---
> >   ArmPkg/Include/IndustryStandard/ArmStdSmc.h                  | 1 +
> >   ArmPkg/Library/ArmPsciResetSystemLib/ArmPsciResetSystemLib.c | 7
> +++++--
> >   2 files changed, 6 insertions(+), 2 deletions(-)
> >
> > Link to github branch for this patch -
> > https://github.com/Pranav-Madhu/edk2/tree/topics/warm_reboot
> >
> > diff --git a/ArmPkg/Include/IndustryStandard/ArmStdSmc.h
> > b/ArmPkg/Include/IndustryStandard/ArmStdSmc.h
> > index 655edc21b205..c9059dead6e9 100644
> > --- a/ArmPkg/Include/IndustryStandard/ArmStdSmc.h
> > +++ b/ArmPkg/Include/IndustryStandard/ArmStdSmc.h
> > @@ -93,6 +93,7 @@
> >   #define ARM_SMC_ID_PSCI_MIGRATE_AARCH32        0x84000005
> >   #define ARM_SMC_ID_PSCI_SYSTEM_OFF             0x84000008
> >   #define ARM_SMC_ID_PSCI_SYSTEM_RESET           0x84000009
> > +#define ARM_SMC_ID_PSCI_SYSTEM_RESET2_AARCH64  0xc4000012
> >
> >   /* The current PSCI version is:  0.2 */
> >   #define ARM_SMC_PSCI_VERSION_MAJOR  0 diff --git
> > a/ArmPkg/Library/ArmPsciResetSystemLib/ArmPsciResetSystemLib.c
> > b/ArmPkg/Library/ArmPsciResetSystemLib/ArmPsciResetSystemLib.c
> > index 7bcd34849507..27e048ba0f7a 100644
> > --- a/ArmPkg/Library/ArmPsciResetSystemLib/ArmPsciResetSystemLib.c
> > +++ b/ArmPkg/Library/ArmPsciResetSystemLib/ArmPsciResetSystemLib.c
> > @@ -45,10 +45,13 @@ LibResetSystem (
> >     ARM_SMC_ARGS  ArmSmcArgs;
> >
> >     switch (ResetType) {
> > +    case EfiResetWarm:
> > +      ArmSmcArgs.Arg0 = ARM_SMC_ID_PSCI_SYSTEM_RESET2_AARCH64;
> > +      ArmSmcArgs.Arg1 = 0;
> > +      ArmSmcArgs.Arg2 = 0;
> > +      break;
> [SAMI] SYSTEM_RESET2 is an optional feature and if not supported would
> return NOT_SUPPORTED. So, if a platform does not support SYSTEM_RESET2,
> should the code here fall back to SYSTEM_RESET?
> According to the PSCI specification, it is the responsibility of the OS to check
> that SYSTEM_RESET2 is supported before calling SYSTEM_RESET2 (I believe this
> is applicable for the case where UEFI is not used to boot the OS). However, if
> the runtime service ResetSystem() is invoked by the OS requesting a warm
> reset, is it not the firmware's responsibility to ensure that SYSTEM_RESET2 is
> supported? Any thoughts?

Right, from PSCI specification, what I understood is before invoking SYSTEM_RESET2, the OS should query the PSCI capabilities using PSCI_FEATURES for SYSTEM_RESET2. The OS should invoke RESET2 only if PSCI_FEATURES returns 0. From spec, what I understood is it is not the responsibility of firmware. If OS issue RESET2 without querying FEATURES, the only option for firmware is to return NOT_SUPPORTED.

> [/SAMI]
> >       case EfiResetPlatformSpecific:
> >       // Map the platform specific reset as reboot
> > -    case EfiResetWarm:
> > -    // Map a warm reset into a cold reset
> >       case EfiResetCold:
> >         // Send a PSCI 0.2 SYSTEM_RESET command
> >         ArmSmcArgs.Arg0 = ARM_SMC_ID_PSCI_SYSTEM_RESET;