Re: [RFC 0/3] Integrate Support for self-save and determine
Thanks for your comments Ram, A list of preferred SPRs are maintained in the kernel which contains two properties: 1. supported_mode: Helps in identifying if it strictly supports self save or restore or both. Will be good to capture the information that, 'supported_mode' gets initialized using the information from the device tree. 2. preferred_mode: Calls out what mode is preferred for each SPR. It could be strictly self save or restore, or it can also determine the preference of mode over the other if both are present by encapsulating the other in bitmask from LSB to MSB. and 'preferred_mode' is statically initialized. Sure thing, I'll mention that. Below is a table to show the Scenario::Consequence when the self save and self restore modes are available or disabled in different combinations as perceived from the device tree thus giving complete backwards compatibly regardless of an older firmware running a newer kernel or vise-versa. SR = Self restore; SS = Self save .---.. | Scenario |Consequence | :---+: | Legacy Firmware. No SS or SR node | Self restore is called for all | | | supported SPRs | :---+: | SR: !active SS: !active | Deep stop states disabled | :---+: | SR: active SS: !active| Self restore is called for all | | | supported SPRs | :---+: | SR: active SS: active | Goes through the preferences for each | | | SPR and executes of the modes | | | accordingly. Currently, Self restore is| | | called for all the SPRs except PSSCR | | | which is self saved| :---+: | SR: active(only HID0) SS: active | Self save called for all supported | | | registers expect HID0 (as HID0 cannot | | | be self saved currently) | Not clear, how this will be conveyed to the hypervisor? Through the device tree or through some other means? This information will be conveyed through the device tree. I'll frame a sentence that makes this more explicit. :---+: | SR: !active SS: active| currently will disable deep states as | | | HID0 is needed to be self restored and | | | cannot be self saved | '---'' Pratik Rajesh Sampat (3): powerpc/powernv: Interface to define support and preference for a SPR powerpc/powernv: Introduce Self save support powerpc/powernv: Parse device tree, population of SPR support arch/powerpc/include/asm/opal-api.h| 3 +- arch/powerpc/include/asm/opal.h| 1 + arch/powerpc/platforms/powernv/idle.c | 431 ++--- arch/powerpc/platforms/powernv/opal-call.c | 1 + 4 files changed, 379 insertions(+), 57 deletions(-) -- 2.21.0
Re: [RFC 0/3] Integrate Support for self-save and determine
On Wed, Dec 04, 2019 at 03:02:52PM +0530, Pratik Rajesh Sampat wrote: > Currently the stop-api supports a mechanism called as self-restore > which allows us to restore the values of certain SPRs on wakeup from a > deep-stop state to a desired value. To use this, the Kernel makes an > OPAL call passing the PIR of the CPU, the SPR number and the value to > which the SPR should be restored when that CPU wakes up from a deep > stop state. > > Recently, a new feature, named self-save has been enabled in the > stop-api, which is an alternative mechanism to do the same, except > that self-save will save the current content of the SPR before > entering a deep stop state and also restore the content back on > waking up from a deep stop state. > > This patch series aims at introducing and leveraging the self-save feature in > the kernel. > > Now, as the kernel has a choice to prefer one mode over the other and > there can be registers in both the save/restore SPR list which are sent > from the device tree, a new interface has been defined for the seamless > handing of the modes for each SPR. > > A list of preferred SPRs are maintained in the kernel which contains two > properties: > 1. supported_mode: Helps in identifying if it strictly supports self >save or restore or both. Will be good to capture the information that, 'supported_mode' gets initialized using the information from the device tree. > 2. preferred_mode: Calls out what mode is preferred for each SPR. It >could be strictly self save or restore, or it can also >determine the preference of mode over the other if both >are present by encapsulating the other in bitmask from >LSB to MSB. and 'preferred_mode' is statically initialized. > Below is a table to show the Scenario::Consequence when the self save and > self restore modes are available or disabled in different combinations as > perceived from the device tree thus giving complete backwards compatibly > regardless of an older firmware running a newer kernel or vise-versa. > > SR = Self restore; SS = Self save > > .---.. > | Scenario |Consequence | > :---+: > | Legacy Firmware. No SS or SR node | Self restore is called for all | > | | supported SPRs | > :---+: > | SR: !active SS: !active | Deep stop states disabled | > :---+: > | SR: active SS: !active| Self restore is called for all | > | | supported SPRs | > :---+: > | SR: active SS: active | Goes through the preferences for each | > | | SPR and executes of the modes | > | | accordingly. Currently, Self restore is| > | | called for all the SPRs except PSSCR | > | | which is self saved| > :---+: > | SR: active(only HID0) SS: active | Self save called for all supported | > | | registers expect HID0 (as HID0 cannot | > | | be self saved currently) | Not clear, how this will be conveyed to the hypervisor? Through the device tree or through some other means? > :---+: > | SR: !active SS: active| currently will disable deep states as | > | | HID0 is needed to be self restored and | > | | cannot be self saved | > '---'' > > Pratik Rajesh Sampat (3): > powerpc/powernv: Interface to define support and preference for a SPR > powerpc/powernv: Introduce Self save support > powerpc/powernv: Parse device tree, population of SPR support > > arch/powerpc/include/asm/opal-api.h| 3 +- > arch/powerpc/include/asm/opal.h| 1 + > arch/powerpc/platforms/powernv/idle.c | 431 ++--- > arch/powerpc/platforms/powernv/opal-call.c | 1 + > 4 files changed, 379 insertions(+), 57 deletions(-) > > -- > 2.21.0 -- Ram Pai
[RFC 0/3] Integrate Support for self-save and determine
Currently the stop-api supports a mechanism called as self-restore which allows us to restore the values of certain SPRs on wakeup from a deep-stop state to a desired value. To use this, the Kernel makes an OPAL call passing the PIR of the CPU, the SPR number and the value to which the SPR should be restored when that CPU wakes up from a deep stop state. Recently, a new feature, named self-save has been enabled in the stop-api, which is an alternative mechanism to do the same, except that self-save will save the current content of the SPR before entering a deep stop state and also restore the content back on waking up from a deep stop state. This patch series aims at introducing and leveraging the self-save feature in the kernel. Now, as the kernel has a choice to prefer one mode over the other and there can be registers in both the save/restore SPR list which are sent from the device tree, a new interface has been defined for the seamless handing of the modes for each SPR. A list of preferred SPRs are maintained in the kernel which contains two properties: 1. supported_mode: Helps in identifying if it strictly supports self save or restore or both. 2. preferred_mode: Calls out what mode is preferred for each SPR. It could be strictly self save or restore, or it can also determine the preference of mode over the other if both are present by encapsulating the other in bitmask from LSB to MSB. Below is a table to show the Scenario::Consequence when the self save and self restore modes are available or disabled in different combinations as perceived from the device tree thus giving complete backwards compatibly regardless of an older firmware running a newer kernel or vise-versa. SR = Self restore; SS = Self save .---.. | Scenario |Consequence | :---+: | Legacy Firmware. No SS or SR node | Self restore is called for all | | | supported SPRs | :---+: | SR: !active SS: !active | Deep stop states disabled | :---+: | SR: active SS: !active| Self restore is called for all | | | supported SPRs | :---+: | SR: active SS: active | Goes through the preferences for each | | | SPR and executes of the modes | | | accordingly. Currently, Self restore is| | | called for all the SPRs except PSSCR | | | which is self saved| :---+: | SR: active(only HID0) SS: active | Self save called for all supported | | | registers expect HID0 (as HID0 cannot | | | be self saved currently) | :---+: | SR: !active SS: active| currently will disable deep states as | | | HID0 is needed to be self restored and | | | cannot be self saved | '---'' Pratik Rajesh Sampat (3): powerpc/powernv: Interface to define support and preference for a SPR powerpc/powernv: Introduce Self save support powerpc/powernv: Parse device tree, population of SPR support arch/powerpc/include/asm/opal-api.h| 3 +- arch/powerpc/include/asm/opal.h| 1 + arch/powerpc/platforms/powernv/idle.c | 431 ++--- arch/powerpc/platforms/powernv/opal-call.c | 1 + 4 files changed, 379 insertions(+), 57 deletions(-) -- 2.21.0
