From: atish.patra@wdc.com (Atish Patra) To: linux-riscv@lists.infradead.org Subject: SBI extension proposal Date: Wed, 31 Oct 2018 11:23:35 -0700 [thread overview] Message-ID: <7f2a546a-6ebb-43c6-83a0-5e712ec2e2c7@wdc.com> (raw) Here is a proposal to make SBI a flexible and extensible interface. It is based on the foundation policy of RISC-V i.e. modularity and openness. It is designed in such a way that it introduces very few new mandatory SBI APIs that are absolutely required to maintain backward compatibility. Everything else is optional so that it remains an open standard yet robust. 1. Introduction: ---------------- The current RISC-V SBI only defines a few mandatory functions such as inter-processor interrupts (IPI) interface, reprogramming timer, serial console and memory barrier instructions. The existing SBI documentation can be found here [1]. Many important functionalities such as power management/cpu-hotplug are not yet defined due to difficulties in accommodating modifications without breaking the backward compatibility with the current interface. Its design is inspired by Power State Coordination Interface (PSCI) from ARM world. However, it adds only two new mandatory SBI calls providing version information and supported APIs, unlike PSCI where a significant number of functions are mandatory. The version of the existing SBI will be defined as a minimum version(0.1) which will always be backward compatible. Similarly, any Linux kernel with newer feature will fall back if an older version of SBI does not support the updated capabilities. Both the operating system and SEE can be implemented to be two way backward compatible. 2. New functions: ----------------- -- u32 sbi_get_version(void): Returns the current SBI version implemented by the firmware. version: uint32: Bits[31:16] Major Version Bits[15:0] Minor Version The existing SBI version can be 0.1. The proposed version will be at 0.2 A different major version may indicate possible incompatible functions. A different minor version must be compatible with each other even if they have a higher number of features. -- u32 sbi_check_api(unsigned long start_api_id, unsigned long count): Accepts a start_api_id as an argument and returns if start_api_id to (start_api_id + count - 1) are supported or not. The API numbering scheme is described in section 3. A count is introduced so that a range of APIs can be checked at one SBI call to minimize the M-mode traps. -- int sbi_hart_up(unsigned long hartid, unsigned long start, unsigned long priv) Brings up "hartid" either during initial boot or after a sbi_hart_down SBI call. "start" points to a runtime-specified address where a hart can enter into supervisor mode. This must be a physical address. "priv" is a private data that caller can use to pass information about execution context. Return the appropriate SBI error code. -- int sbi_hart_suspend(u32 state, unsigned long resume_entry, unsigned long priv) Suspends the calling hart to a particular power state. Suspended hart will automatically wake-up based on some wakeup events at resume_entry physical address. "priv" is a private data that caller can use to pass information about execution context. The SBI implementation must save a copy so that caller can reuse while restoring hart from suspend. Return the appropriate SBI error code. -- int sbi_hart_down() It powers off the hart and will be used in cpu-hotplug. Only individual hart can remove itself from supervisor mode. It can be moved to normal state only by sbi_hart_up function. Return the appropriate SBI error code. -- u32 sbi_hart_state(unsigned long hartid) Returns the RISCV_POWER_STATE for a specific hartid. This will help make kexec like functionality more robust. -- void sbi_system_shutdown() Powers off the entire system. 3. SBI API ID numbering scheme: ------------------------------ An API Set is a set of SBI APIs which collectively implement some kind of feature/functionality. Let's say SBI API ID is u32 then Bit[31:24] = API Set Number Bit[23:0] = API Number within API Set Here are few API Sets for SBI v0.2: 1. Base APIs API Set Number: 0x0 Description: Base APIs mandatory for any SBI version 2. HART PM APIs API Set Number: 0x1 Description: Hart UP/Down/Suspend APIs for per-Hart power management 3. System PM APIs API Set Number; 0x2 Description: System Shutdown/Reboot/Suspend for system-level power management 4. Vendor APIs API Set Number: 0xff Description: Vendor specific APIs. There is a possibility that different vendors can choose to assign same API numbers for different functionality. In that case, vendor specific strings in Device Tree can be used to verify if a specific API belongs to the intended vendor or not. 4. Return error code Table: --------------------------- Here are the SBI return error codes defined. SBI_SUCCESS 0 SBI_NOT_SUPPORTED -1 SBI_INVALID_PARAM -2 SBI_DENIED -3 SBI_INVALID_ADDRESS -4 A mapping function between SBI error code & Linux error code should be provided. 5. Power State -------------- A RISC-V core can exist in any of the following power states. enum RISCV_POWER_STATE { //Powered up & operational. RISCV_HART_ON = 0, //Powered up but at reduced energy consumption. WFI instruction can be used to achieve this state. RISCV_HART_STANDBY = 1, //Deeper low power state. No reset required but higher wakeup latency. RISCV_HART_RETENTION = 2, //Powered off. Reset of the core required after power restore. RISCV_HART_OFF = 3 } TODO: Any other power management related features or state? 6. Implementation ------------------- Currently, SBI is implemented as a part of BBL. There is a different SBI implementation available in coreboot as well. Alternatively, a separate open BSD/MIT licensed SBI project can be created which can be used by anybody to avoid these kind of SBI fragmentation in future. This project can generate both a firmware binary (to executed directly in M mode) or a static library that can be used by different boot loaders. It will also help individual boot loaders to either work from M or S mode without a separate SBI implementation. This proposal is far from perfect and absolutely any suggestion is welcome. Obviously, there are many other functionalities that can be added or removed from this proposal. However, I just wanted to start with something that is an incremental change at best to kick off the discussion. The aim here is initiate a discussion that can lead to a robust SBI specification. Looking forward to discuss other ideas as well or any feedback on this proposal. Reference: ----------- [1] http://infocenter.arm.com/help/topic/com.arm.doc.den0022d/Power_State_Coordination_Interface_PDD_v1_1_DEN0022D.pdf [2] https://github.com/riscv/riscv-sbi-doc/blob/master/riscv-sbi.md Regards, Atish
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From: Atish Patra <atish.patra@wdc.com> To: "linux-riscv@lists.infradead.org" <linux-riscv@lists.infradead.org> Cc: "mark.rutland@arm.com" <mark.rutland@arm.com>, Zong Li <zong@andestech.com>, Damien Le Moal <Damien.LeMoal@wdc.com>, Olof Johansson <olof.johansson@gmail.com>, Andrew Waterman <andrew@sifive.com>, Alan Kao <alankao@andestech.com>, Anup Patel <anup@brainfault.org>, Palmer Dabbelt <palmer@sifive.com>, "Rwmjones.fedora" <rjones@redhat.com>, Christoph Hellwig <hch@infradead.org>, "vincentc@andestech.com" <vincentc@andestech.com>, Michael Clark <mjc@sifive.com>, Arnd Bergmann <arnd@arndb.de>, Paul Walmsley <paul.walmsley@sifive.com>, "Chang, Abner \(HPS SW/FW Technologist\)" <abner.chang@hpe.com>, David.Abdurachmanov@cern.ch Subject: SBI extension proposal Date: Wed, 31 Oct 2018 11:23:35 -0700 [thread overview] Message-ID: <7f2a546a-6ebb-43c6-83a0-5e712ec2e2c7@wdc.com> (raw) Message-ID: <20181031182335.KF-rBtLMJg44fJj-2aZ79w-uHP5wYS7kyaVEBPV403E@z> (raw) Here is a proposal to make SBI a flexible and extensible interface. It is based on the foundation policy of RISC-V i.e. modularity and openness. It is designed in such a way that it introduces very few new mandatory SBI APIs that are absolutely required to maintain backward compatibility. Everything else is optional so that it remains an open standard yet robust. 1. Introduction: ---------------- The current RISC-V SBI only defines a few mandatory functions such as inter-processor interrupts (IPI) interface, reprogramming timer, serial console and memory barrier instructions. The existing SBI documentation can be found here [1]. Many important functionalities such as power management/cpu-hotplug are not yet defined due to difficulties in accommodating modifications without breaking the backward compatibility with the current interface. Its design is inspired by Power State Coordination Interface (PSCI) from ARM world. However, it adds only two new mandatory SBI calls providing version information and supported APIs, unlike PSCI where a significant number of functions are mandatory. The version of the existing SBI will be defined as a minimum version(0.1) which will always be backward compatible. Similarly, any Linux kernel with newer feature will fall back if an older version of SBI does not support the updated capabilities. Both the operating system and SEE can be implemented to be two way backward compatible. 2. New functions: ----------------- -- u32 sbi_get_version(void): Returns the current SBI version implemented by the firmware. version: uint32: Bits[31:16] Major Version Bits[15:0] Minor Version The existing SBI version can be 0.1. The proposed version will be at 0.2 A different major version may indicate possible incompatible functions. A different minor version must be compatible with each other even if they have a higher number of features. -- u32 sbi_check_api(unsigned long start_api_id, unsigned long count): Accepts a start_api_id as an argument and returns if start_api_id to (start_api_id + count - 1) are supported or not. The API numbering scheme is described in section 3. A count is introduced so that a range of APIs can be checked at one SBI call to minimize the M-mode traps. -- int sbi_hart_up(unsigned long hartid, unsigned long start, unsigned long priv) Brings up "hartid" either during initial boot or after a sbi_hart_down SBI call. "start" points to a runtime-specified address where a hart can enter into supervisor mode. This must be a physical address. "priv" is a private data that caller can use to pass information about execution context. Return the appropriate SBI error code. -- int sbi_hart_suspend(u32 state, unsigned long resume_entry, unsigned long priv) Suspends the calling hart to a particular power state. Suspended hart will automatically wake-up based on some wakeup events at resume_entry physical address. "priv" is a private data that caller can use to pass information about execution context. The SBI implementation must save a copy so that caller can reuse while restoring hart from suspend. Return the appropriate SBI error code. -- int sbi_hart_down() It powers off the hart and will be used in cpu-hotplug. Only individual hart can remove itself from supervisor mode. It can be moved to normal state only by sbi_hart_up function. Return the appropriate SBI error code. -- u32 sbi_hart_state(unsigned long hartid) Returns the RISCV_POWER_STATE for a specific hartid. This will help make kexec like functionality more robust. -- void sbi_system_shutdown() Powers off the entire system. 3. SBI API ID numbering scheme: ------------------------------ An API Set is a set of SBI APIs which collectively implement some kind of feature/functionality. Let's say SBI API ID is u32 then Bit[31:24] = API Set Number Bit[23:0] = API Number within API Set Here are few API Sets for SBI v0.2: 1. Base APIs API Set Number: 0x0 Description: Base APIs mandatory for any SBI version 2. HART PM APIs API Set Number: 0x1 Description: Hart UP/Down/Suspend APIs for per-Hart power management 3. System PM APIs API Set Number; 0x2 Description: System Shutdown/Reboot/Suspend for system-level power management 4. Vendor APIs API Set Number: 0xff Description: Vendor specific APIs. There is a possibility that different vendors can choose to assign same API numbers for different functionality. In that case, vendor specific strings in Device Tree can be used to verify if a specific API belongs to the intended vendor or not. 4. Return error code Table: --------------------------- Here are the SBI return error codes defined. SBI_SUCCESS 0 SBI_NOT_SUPPORTED -1 SBI_INVALID_PARAM -2 SBI_DENIED -3 SBI_INVALID_ADDRESS -4 A mapping function between SBI error code & Linux error code should be provided. 5. Power State -------------- A RISC-V core can exist in any of the following power states. enum RISCV_POWER_STATE { //Powered up & operational. RISCV_HART_ON = 0, //Powered up but at reduced energy consumption. WFI instruction can be used to achieve this state. RISCV_HART_STANDBY = 1, //Deeper low power state. No reset required but higher wakeup latency. RISCV_HART_RETENTION = 2, //Powered off. Reset of the core required after power restore. RISCV_HART_OFF = 3 } TODO: Any other power management related features or state? 6. Implementation ------------------- Currently, SBI is implemented as a part of BBL. There is a different SBI implementation available in coreboot as well. Alternatively, a separate open BSD/MIT licensed SBI project can be created which can be used by anybody to avoid these kind of SBI fragmentation in future. This project can generate both a firmware binary (to executed directly in M mode) or a static library that can be used by different boot loaders. It will also help individual boot loaders to either work from M or S mode without a separate SBI implementation. This proposal is far from perfect and absolutely any suggestion is welcome. Obviously, there are many other functionalities that can be added or removed from this proposal. However, I just wanted to start with something that is an incremental change at best to kick off the discussion. The aim here is initiate a discussion that can lead to a robust SBI specification. Looking forward to discuss other ideas as well or any feedback on this proposal. Reference: ----------- [1] http://infocenter.arm.com/help/topic/com.arm.doc.den0022d/Power_State_Coordination_Interface_PDD_v1_1_DEN0022D.pdf [2] https://github.com/riscv/riscv-sbi-doc/blob/master/riscv-sbi.md Regards, Atish _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv
next reply other threads:[~2018-10-31 18:23 UTC|newest] Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-10-31 18:23 Atish Patra [this message] 2018-10-31 18:23 ` SBI extension proposal Atish Patra [not found] ` <CAK-hmcQeiGa3BwnzEVB_dyhFiC7rXHFN-wTsJomg-jAo7a+v3Q@mail.gmail.com> 2018-10-31 19:11 ` Olof Johansson 2018-10-31 19:11 ` Olof Johansson 2018-10-31 20:37 ` Atish Patra 2018-10-31 20:37 ` Atish Patra 2018-11-02 6:31 ` Chang, Abner (HPS SW/FW Technologist) 2018-11-02 6:31 ` Chang, Abner (HPS SW/FW Technologist) 2018-11-02 22:31 ` Atish Patra 2018-11-02 22:31 ` Atish Patra 2018-11-04 14:36 ` Chang, Abner (HPS SW/FW Technologist) 2018-11-04 14:36 ` Chang, Abner (HPS SW/FW Technologist) [not found] ` <CA+h06zgcyWz7WMbzQxjyc9V5S3CokqSoO1mGOaynJE3uJE5QSg@mail.gmail.com> 2018-11-01 9:35 ` Anup Patel 2018-11-01 9:35 ` Anup Patel 2018-11-01 9:46 ` Richard W.M. Jones 2018-11-01 9:46 ` Richard W.M. Jones 2018-11-01 11:03 ` Philipp Hug 2018-11-01 11:03 ` Philipp Hug 2018-11-01 11:25 ` Richard W.M. Jones 2018-11-01 11:25 ` Richard W.M. Jones 2018-11-01 15:09 ` Atish Patra 2018-11-01 15:09 ` Atish Patra 2018-11-02 3:17 ` Olof Johansson 2018-11-02 3:17 ` Olof Johansson 2018-11-01 16:42 ` Karsten Merker 2018-11-02 2:49 ` Palmer Dabbelt 2018-11-02 2:49 ` Palmer Dabbelt 2018-11-02 3:27 ` Anup Patel 2018-11-02 3:27 ` Anup Patel 2018-11-02 4:29 ` Chang, Abner (HPS SW/FW Technologist) 2018-11-02 4:29 ` Chang, Abner (HPS SW/FW Technologist) 2018-11-02 15:24 ` Nick Kossifidis 2018-11-02 15:24 ` Nick Kossifidis 2018-11-02 23:12 ` Atish Patra 2018-11-02 23:12 ` Atish Patra 2018-11-02 23:45 ` Nick Kossifidis 2018-11-02 23:45 ` Nick Kossifidis 2018-11-03 0:00 ` Atish Patra 2018-11-03 0:00 ` Atish Patra 2018-11-05 13:50 ` Nick Kossifidis 2018-11-05 13:50 ` Nick Kossifidis 2018-11-05 18:51 ` Atish Patra 2018-11-05 18:51 ` Atish Patra 2018-11-06 1:55 ` Zong Li 2018-11-06 1:55 ` Zong Li 2018-11-09 21:47 ` Atish Patra 2018-11-09 21:47 ` Atish Patra
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