PCI: dwc: drop dependency on ZONE_DMA32

Re-work the msi_msg DMA allocation logic to use dma_alloc_coherent()
which uses the coherent DMA mask to try and return an allocation within
the DMA mask limits. This allows kernel configurations that disable
ZONE_DMA32 to continue supporting a 32-bit DMA mask. Without this patch,
the PCIe host device will fail to probe when ZONE_DMA32 is disabled.

Fixes: 35797e6 ("PCI: dwc: Fix MSI msi_msg DMA mapping")
Signed-off-by: Will McVicker <willmcvicker@google.com>

drivers/pci/controller/dwc/pcie-designware-host.c

@@ -272,9 +272,9 @@ static void dw_pcie_free_msi(struct dw_pcie_rp *pp)
 		struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
 		struct device *dev = pci->dev;
 
-		dma_unmap_page(dev, pp->msi_data, PAGE_SIZE, DMA_FROM_DEVICE);
-		if (pp->msi_page)
-			__free_page(pp->msi_page);
+		dma_free_coherent(dev, PAGE_SIZE, pp->msi_page, pp->msi_data);
+		pp->msi_data = 0;
+		pp->msi_page = NULL;
 	}
 }
 
@@ -375,22 +375,22 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
 						    dw_chained_msi_isr, pp);
 	}
 
-	ret = dma_set_mask(dev, DMA_BIT_MASK(32));
+	ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32));
 	if (ret)
 		dev_warn(dev, "Failed to set DMA mask to 32-bit. Devices with only 32-bit MSI support may not work properly\n");
 
-	pp->msi_page = alloc_page(GFP_DMA32);
-	pp->msi_data = dma_map_page(dev, pp->msi_page, 0,
-				    PAGE_SIZE, DMA_FROM_DEVICE);
-	ret = dma_mapping_error(dev, pp->msi_data);
-	if (ret) {
-		dev_err(pci->dev, "Failed to map MSI data\n");
-		__free_page(pp->msi_page);
-		pp->msi_page = NULL;
+	pp->msi_page = dma_alloc_coherent(dev, PAGE_SIZE, &pp->msi_data,
+					  GFP_KERNEL);
+	if (!pp->msi_page || dma_mapping_error(dev, pp->msi_data)) {
+		dev_err(dev, "Failed to alloc and map MSI data\n");
+		if (pp->msi_page) {
+			dma_free_coherent(dev, PAGE_SIZE, pp->msi_page,
+					  pp->msi_data);
+			pp->msi_page = NULL;
+		}
 		pp->msi_data = 0;
 		dw_pcie_free_msi(pp);
-
-		return ret;
+		return -ENOMEM;
 	}
 
 	return 0;