linux-kernel - [PATCH V4] PCI: loongson: Skip scanning unavailable child devices

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Date:   Tue,  8 Nov 2022 14:42:40 +0800
From:   Liu Peibao <liupeibao@...ngson.cn>
To:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     Huacai Chen <chenhuacai@...ngson.cn>,
        Jianmin Lv <lvjianmin@...ngson.cn>,
        Yinbo Zhu <zhuyinbo@...ngson.cn>,
        Liu Peibao <liupeibao@...ngson.cn>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH V4] PCI: loongson: Skip scanning unavailable child devices

The PCI Controller of 2k1000 could not mask devices by setting vender ID or
device ID in configuration space header as invalid values. When there are
pins shareable between the platform device and PCI device, if the platform
device is preferred, we should not scan this PCI device. In the above
scene, add `status = "disabled"` property in DT node of this PCI device.

Signed-off-by: Liu Peibao <liupeibao@...ngson.cn>
---
V3 -> V4: 1. get rid of the masklist and search the status property
	  directly.
          2. check the status property only when accessing the vendor ID.
V2 -> V3: 1. use list_for_each_entry() for more clearly.
          2. fix wrong use of sizeof().
V1 -> V2: use existing property "status" instead of adding new property.

 drivers/pci/controller/pci-loongson.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/pci/controller/pci-loongson.c b/drivers/pci/controller/pci-loongson.c
index 05c50408f13b..efca0b3b5a29 100644
--- a/drivers/pci/controller/pci-loongson.c
+++ b/drivers/pci/controller/pci-loongson.c
@@ -194,6 +194,17 @@ static void __iomem *pci_loongson_map_bus(struct pci_bus *bus,
 			return NULL;
 	}
 
+#ifdef CONFIG_OF
+	/* Don't access disabled devices. */
+	if (pci_is_root_bus(bus) && where == PCI_VENDOR_ID) {
+		struct device_node *dn;
+
+		dn = of_pci_find_child_device(bus->dev.of_node, devfn);
+		if (dn && !of_device_is_available(dn))
+			return NULL;
+	}
+#endif
+
 	/* CFG0 can only access standard space */
 	if (where < PCI_CFG_SPACE_SIZE && priv->cfg0_base)
 		return cfg0_map(priv, bus, devfn, where);
-- 
2.20.1