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From: Boqun Feng <boqun.feng@gmail.com>
To: Bjorn Helgaas <bhelgaas@google.com>,
	Arnd Bergmann <arnd@arndb.de>, Marc Zyngier <maz@kernel.org>
Cc: "Catalin Marinas" <catalin.marinas@arm.com>,
	"Will Deacon" <will@kernel.org>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	"Haiyang Zhang" <haiyangz@microsoft.com>,
	"Stephen Hemminger" <sthemmin@microsoft.com>,
	"Wei Liu" <wei.liu@kernel.org>,
	"Dexuan Cui" <decui@microsoft.com>,
	"Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
	"Rob Herring" <robh@kernel.org>,
	"Krzysztof Wilczyński" <kw@linux.com>,
	"Boqun Feng" <boqun.feng@gmail.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org,
	linux-pci@vger.kernel.org,
	"Sunil Muthuswamy" <sunilmut@microsoft.com>,
	"Mike Rapoport" <rppt@kernel.org>
Subject: [RFC v5 4/8] arm64: PCI: Support root bridge preparation for Hyper-V
Date: Tue, 20 Jul 2021 21:44:25 +0800	[thread overview]
Message-ID: <20210720134429.511541-5-boqun.feng@gmail.com> (raw)
In-Reply-To: <20210720134429.511541-1-boqun.feng@gmail.com>

Currently at root bridge preparation, the corresponding ACPI device will
be set as the companion, however for a Hyper-V virtual PCI root bridge,
there is no corresponding ACPI device, because a Hyper-V virtual PCI
root bridge is discovered via VMBus rather than ACPI table. In order to
support this, we need to make pcibios_root_bridge_prepare() work with
cfg->parent being NULL.

Use a NULL pointer as the ACPI device if there is no corresponding ACPI
device, and this is fine because: 1) ACPI_COMPANION_SET() can work with
the second parameter being NULL, 2) semantically, if a NULL pointer is
set via ACPI_COMPANION_SET(), ACPI_COMPANION() (the read API for this
field) will return NULL, and since ACPI_COMPANION() may return NULL, so
users must have handled the cases where it returns NULL, and 3) since
there is no corresponding ACPI device, it would be wrong to use any
other value here.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 arch/arm64/kernel/pci.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/pci.c b/arch/arm64/kernel/pci.c
index 5148ae242780..2276689b5411 100644
--- a/arch/arm64/kernel/pci.c
+++ b/arch/arm64/kernel/pci.c
@@ -90,7 +90,17 @@ int pcibios_root_bridge_prepare(struct pci_host_bridge *bridge)
 		return 0;
 
 	cfg = bridge->bus->sysdata;
-	adev = to_acpi_device(cfg->parent);
+
+	/*
+	 * On Hyper-V there is no corresponding ACPI device for a root bridge,
+	 * therefore ->parent is set as NULL by the driver. And set 'adev' as
+	 * NULL in this case because there is no proper ACPI device.
+	 */
+	if (!cfg->parent)
+		adev = NULL;
+	else
+		adev = to_acpi_device(cfg->parent);
+
 	bus_dev = &bridge->bus->dev;
 
 	ACPI_COMPANION_SET(&bridge->dev, adev);
-- 
2.30.2


  parent reply	other threads:[~2021-07-20 14:02 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-20 13:44 [RFC v5 0/8] PCI: hv: Support host bridge probing on ARM64 Boqun Feng
2021-07-20 13:44 ` [RFC v5 1/8] PCI: Introduce domain_nr in pci_host_bridge Boqun Feng
2021-07-20 22:49   ` Bjorn Helgaas
2021-07-21  0:57     ` Boqun Feng
2021-07-20 13:44 ` [RFC v5 2/8] PCI: Support populating MSI domains of root buses via bridges Boqun Feng
2021-07-20 13:44 ` [RFC v5 3/8] arm64: PCI: Restructure pcibios_root_bridge_prepare() Boqun Feng
2021-07-20 13:44 ` Boqun Feng [this message]
2021-07-20 13:44 ` [RFC v5 5/8] PCI: hv: Generify PCI probing Boqun Feng
2021-07-20 13:44 ` [RFC v5 6/8] PCI: hv: Set ->domain_nr of pci_host_bridge at probing time Boqun Feng
2021-07-20 13:44 ` [RFC v5 7/8] PCI: hv: Set up MSI domain at bridge " Boqun Feng
2021-07-20 13:44 ` [RFC v5 8/8] PCI: hv: Turn on the host bridge probing on ARM64 Boqun Feng
2021-07-20 14:38   ` Marc Zyngier
2021-07-20 14:59     ` Boqun Feng
2021-07-20 15:53       ` Marc Zyngier

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