PCI: aardvark: Read all 16-bits from PCIE_MSI_PAYLOAD_REG

The PCIE_MSI_PAYLOAD_REG contains 16-bit MSI number, not only lower
8 bits. Fix reading content of this register and add a comment
describing the access to this register.

Link: https://lore.kernel.org/r/20211028185659.20329-4-kabel@kernel.org
Fixes: 8c39d710 ("PCI: aardvark: Add Aardvark PCI host controller driver")
Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: stable@vger.kernel.org

drivers/pci/controller/pci-aardvark.c

@@ -119,6 +119,7 @@
 #define PCIE_MSI_STATUS_REG			(CONTROL_BASE_ADDR + 0x58)
 #define PCIE_MSI_MASK_REG			(CONTROL_BASE_ADDR + 0x5C)
 #define PCIE_MSI_PAYLOAD_REG			(CONTROL_BASE_ADDR + 0x9C)
+#define     PCIE_MSI_DATA_MASK			GENMASK(15, 0)
 
 /* PCIe window configuration */
 #define OB_WIN_BASE_ADDR			0x4c00
@@ -1319,8 +1320,12 @@ static void advk_pcie_handle_msi(struct advk_pcie *pcie)
 		if (!(BIT(msi_idx) & msi_status))
 			continue;
 
+		/*
+		 * msi_idx contains bits [4:0] of the msi_data and msi_data
+		 * contains 16bit MSI interrupt number
+		 */
 		advk_writel(pcie, BIT(msi_idx), PCIE_MSI_STATUS_REG);
-		msi_data = advk_readl(pcie, PCIE_MSI_PAYLOAD_REG) & 0xFF;
+		msi_data = advk_readl(pcie, PCIE_MSI_PAYLOAD_REG) & PCIE_MSI_DATA_MASK;
 		generic_handle_irq(msi_data);
 	}