PCI: mediatek: Advertise lack of built-in MSI handling

Some Mediatek host bridges cannot handle MSIs, which is sad.
This also results in an ugly warning at device probe time,
as the core PCI code wasn't told that MSIs were not available.

Advertise this fact to the rest of the core PCI code by
using the 'msi_domain' attribute, which still opens the possibility
for another block to provide the MSI functionnality.

[maz: commit message, switched over to msi_domain attribute]

Link: https://lore.kernel.org/r/20210330151145.997953-13-maz@kernel.org
Reported-by: Frank Wunderlich <frank-w@public-files.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>

Author: KAGA-KOKO

drivers/pci/controller/pcie-mediatek.c

@@ -143,6 +143,7 @@ struct mtk_pcie_port;
  * struct mtk_pcie_soc - differentiate between host generations
  * @need_fix_class_id: whether this host's class ID needed to be fixed or not
  * @need_fix_device_id: whether this host's device ID needed to be fixed or not
+ * @no_msi: Bridge has no MSI support, and relies on an external block
  * @device_id: device ID which this host need to be fixed
  * @ops: pointer to configuration access functions
  * @startup: pointer to controller setting functions
@@ -151,6 +152,7 @@ struct mtk_pcie_port;
 struct mtk_pcie_soc {
 	bool need_fix_class_id;
 	bool need_fix_device_id;
+	bool no_msi;
 	unsigned int device_id;
 	struct pci_ops *ops;
 	int (*startup)(struct mtk_pcie_port *port);
@@ -1087,6 +1089,7 @@ static int mtk_pcie_probe(struct platform_device *pdev)
 
 	host->ops = pcie->soc->ops;
 	host->sysdata = pcie;
+	host->msi_domain = pcie->soc->no_msi;
 
 	err = pci_host_probe(host);
 	if (err)
@@ -1176,6 +1179,7 @@ static const struct dev_pm_ops mtk_pcie_pm_ops = {
 };
 
 static const struct mtk_pcie_soc mtk_pcie_soc_v1 = {
+	.no_msi = true,
 	.ops = &mtk_pcie_ops,
 	.startup = mtk_pcie_startup_port,
 };