W dniu 14.03.2024 o 16:13, Ard Biesheuvel pisze:
+++ b/Silicon/Qemu/SbsaQemu/Drivers/SbsaQemuPlatformDxe/SbsaQemuPlatformDxe.inf
@@ -1,7 +1,7 @@
## @file
# This driver effectuates SbsaQemu platform configuration settings
#
-# Copyright (c) 2019, Linaro Ltd. All rights reserved.
+# Copyright (c) Linaro Ltd. All rights reserved.
#
# SPDX-License-Identifier: BSD-2-Clause-Patent
#
@@ -32,6 +32,7 @@ [LibraryClasses]
PcdLib
DebugLib
NonDiscoverableDeviceRegistrationLib
+ SbsaQemuHardwareInfoLib
UefiDriverEntryPoint
[Pcd]
@@ -46,6 +47,7 @@ [Pcd]
gArmTokenSpaceGuid.PcdGicDistributorBase
gArmTokenSpaceGuid.PcdGicRedistributorsBase
gArmVirtSbsaQemuPlatformTokenSpaceGuid.PcdGicItsBase
+ gArmVirtSbsaQemuPlatformTokenSpaceGuid.PcdCoreCount
[Depex]
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.
This is why PCDs suck for dynamic information, to be honest. Much
better to use a protocol (DEPEXes declare dependencies on protocols,
so a driver will never run before the protocols it depends on have
been made available)
I am still learning. Will look at other platforms.
Given that this is intended as reference code, I think it is very
important to get this right.
Fully agree.
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