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Why can't Linux call SBI reset directly?
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Heinrich Schuchardt
On Fri, Sep 10, 2021 at 3:19 PM Heinrich Schuchardt wrote:
The platform specification makes it clear that reset drivers shouldsit in SBI and that Linux should rely on UEFI firmware calling it. On 9/10/21 9:26 AM, Bin Meng wrote: Why can't Linux call SBI reset directly?Hello Bin, I am copying in tech-unixplatformspec@... because we should add a reason for this design decision in the specification. Linux' efi_reboot() in drivers/firmware/efi/reboot.c checks if a capsule update is ongoing. The UEFI firmware may rely on being informed of a reset for cleanup tasks like adding an event log entry or preparing for a capsule update. ResetSystem() has parameter ResetData to pass a message with a reset reason which Linux currently is not using. Best regards Heinrich |
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On 10/09/21, 1:49 PM, "tech-unixplatformspec@... on behalf of Heinrich Schuchardt" <tech-unixplatformspec@... on behalf of heinrich.schuchardt@...> wrote:
On Fri, Sep 10, 2021 at 3:19 PM Heinrich Schuchardt wrote: > The platform specification makes it clear that reset drivers should sit in SBI and that Linux should rely on UEFI firmware calling it. On 9/10/21 9:26 AM, Bin Meng wrote: > Why can't Linux call SBI reset directly? Hello Bin, I am copying in tech-unixplatformspec@... because we should add a reason for this design decision in the specification. Linux' efi_reboot() in drivers/firmware/efi/reboot.c checks if a capsule update is ongoing. The UEFI firmware may rely on being informed of a reset for cleanup tasks like adding an event log entry or preparing for a capsule update. ResetSystem() has parameter ResetData to pass a message with a reset reason which Linux currently is not using. [Anup] While I mostly agree with you but we have cases (such as Linux running inside Guest/VM under hypervisor) where UEFI runtime services might not be always available so Linux use UEFI system reset whenever available otherwise fallback to directly using SBI reset. This is what even ARM does. Regards, Anup Best regards Heinrich |
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Bin Meng
On Fri, Sep 10, 2021 at 6:53 PM Anup Patel <Anup.Patel@...> wrote:
This is my understanding as well. We should not force Linux to only call EFI runtime services to do the reboot. Regards, Bin |
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On Fri, Sep 10, 2021 at 1:48 PM Heinrich Schuchardt
<heinrich.schuchardt@...> wrote: It seems there is a confusion in interpreting platform spec reset related requirement. This requirement only applies to RISC-V platforms claiming OS-A platform compliance but Linux will be supporting much more platforms in addition to OS-A platforms so Linux kernel will have to fallback to directly calling SBI reset when UEFI runtime services are not available. Regards, Anup
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Rahul Pathak
The explicit reset example in the spec is from the perspective of the firmware implementation. But from the OS usage perspective, it clearly states that EFI interfaces should be given the priority before SBI and other platform specific mechanisms. On Fri, Sep 10, 2021 at 5:39 PM Anup Patel <anup@...> wrote: On Fri, Sep 10, 2021 at 1:48 PM Heinrich Schuchardt |
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