Re: [edk2-devel] [PATCH edk2-platforms v6 2/7] Platform/SbsaQemu: read amount of cpus during init

["Marcin Juszkiewicz" <marcin.juszkiewicz@linaro.org>]

W dniu 15.03.2024 o 12:49, Marcin Juszkiewicz pisze:
> W dniu 14.03.2024 o 16:13, Ard Biesheuvel pisze:

>> How is it guaranteed that other components will only see the correct
>> core count? DXE dispatch is ordered using a dependency graph, so all
>> users of this PCD should never execute before this driver.
> 
> SbsaQemuPlatformDxe is a DXE, right? So it is called on platform init.
> 
> At the end of initialization it calls SbsaQemuGetCpuCount() from 
> SbsaQemuHardwareInfoLib to SET this PCD. It does not use it during 
> platform init cause it does not require this information. But calls 
> function to make sure that amount of cpus is known to whatever will be 
> called later.
> 
> Sure, maybe SbsaQemuHardwareInfoLib should be something else (DXE, 
> Protocol or other EDK2 magic thing) but it is set of functions to be 
> called from other places of EDK2.

EDK2 starts and one of the first DXE called is SbsaQemuPlatformDxe one:

InitializeSbsaQemuPlatformDxe: InitializeSbsaQemuPlatformDxe called

InitializeSbsaQemuPlatformDxe: Got platform AHCI 60100000 65536

INFO:    SMC call: (0xc2000001) (function id: 1)

INFO:    Platform version requested

Platform version: 0.3

INFO:    SMC call: (0xc2000064) (function id: 100)

GICD base: 0x40060000

GICR base: 0x40080000

INFO:    SMC call: (0xc2000065) (function id: 101)

GICI base: 0x44081000

InitializeSbsaQemuPlatformDxe: Got platform XHCI 60110000 65536

INFO:    SMC call: (0xc20000c8) (function id: 200)

We have 4 cpus.


It does:

- AHCI init
- Platform version
- GIC addresses
- GIC ITS address
- XHCI init
- CPU count

Then system boot continues with 
gArmVirtSbsaQemuPlatformTokenSpaceGuid.PcdCoreCount being set to proper 
value.

If replacing use of Pcd with calls to SbsaQemuGetCpuCount() look better 
then I can change code to make it happen.


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