[PATCH v7 23/25] PCI: dwc: Restore DMA-mask after MSI-data allocation

[Serge Semin <Sergey.Semin@baikalelectronics.ru>]

DW PCIe Root Ports and End-points can be equipped with the DW eDMA engine.
In that case it is critical to have the platform device pre-initialized
with a valid DMA-mask so the drivers using the eDMA-engine would be able
to allocate the DMA-able buffers. The MSI-capable data requires to be
allocated from the lowest 4GB region. Since that procedure implies the
DMA-mask change we need to restore the mask set by the low-level drivers
after the MSI-data allocation is done.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>

---

Changelog v7:
- This is a new patch added on v7 stage of the series. (@Robin)
---
 drivers/pci/controller/dwc/pcie-designware-host.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
index 5762bd306261..1a3dae1f6aa2 100644
--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/drivers/pci/controller/dwc/pcie-designware-host.c
@@ -326,7 +326,7 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
 	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
 	struct device *dev = pci->dev;
 	struct platform_device *pdev = to_platform_device(dev);
-	u64 *msi_vaddr;
+	u64 *msi_vaddr, dma_mask;
 	int ret;
 	u32 ctrl, num_ctrls;
 
@@ -366,6 +366,13 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
 						    dw_chained_msi_isr, pp);
 	}
 
+	/*
+	 * Save and then restore the DMA-mask pre-set by the low-level drivers
+	 * after allocating the MSI-capable region. The mask might be useful for
+	 * the controllers with the embedded eDMA engine.
+	 */
+	dma_mask = dma_get_mask(dev);
+
 	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");
@@ -378,6 +385,10 @@ static int dw_pcie_msi_host_init(struct dw_pcie_rp *pp)
 		return -ENOMEM;
 	}
 
+	ret = dma_set_mask_and_coherent(dev, dma_mask);
+	if (ret)
+		dev_warn(dev, "Failed to re-store DMA-mask\n");
+
 	return 0;
 }
 
-- 
2.38.1