[PATCH V3] PCI: tegra: Use the DMA-API to get the MSI address

[Vidya Sagar <vidyas@xxxxxxxxxx>]

Since the upstream MSI memory writes are generated by downstream devices,
it is logically correct to have MSI target memory coming from the DMA pool
reserved for PCIe than from the general memory pool reserved for CPU
access. This avoids PCIe DMA addresses coinciding with MSI target address
thereby raising unwanted MSI interrupts. This patch also enforces to limit
the MSI target address to 32-bits to make it work for PCIe endponits that
support only 32-bit MSI target address and those endpoints that support
64-bit MSI target address anyway work with 32-bit MSI target address.

Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>
Reviewed-by: Thierry Reding <treding@xxxxxxxxxx>
Acked-by: Thierry Reding <treding@xxxxxxxxxx>
---
v3:
* replaced dma_alloc_coherent(), dma_free_coherent() APIs with
  dma_alloc_attrs(), dma_free_attrs() APIs along with
  DMA_ATTR_NO_KERNEL_MAPPING flag to indicate that there is no
  need to create kernel mapping for it.

v2:
* changed 'phys' type to 'dma_addr_t' from 'u64'
* added a comment on why DMA mask is set to 32-bit
* replaced 'dma' with 'DMA'

 drivers/pci/controller/pci-tegra.c | 37 ++++++++++++++++++++++--------
 1 file changed, 28 insertions(+), 9 deletions(-)

diff --git a/drivers/pci/controller/pci-tegra.c b/drivers/pci/controller/pci-tegra.c
index f4f53d092e00..464ba2538d52 100644
--- a/drivers/pci/controller/pci-tegra.c
+++ b/drivers/pci/controller/pci-tegra.c
@@ -231,9 +231,9 @@ struct tegra_msi {
 	struct msi_controller chip;
 	DECLARE_BITMAP(used, INT_PCI_MSI_NR);
 	struct irq_domain *domain;
-	unsigned long pages;
 	struct mutex lock;
-	u64 phys;
+	void *virt;
+	dma_addr_t phys;
 	int irq;
 };
 
@@ -1536,7 +1536,7 @@ static int tegra_pcie_msi_setup(struct tegra_pcie *pcie)
 	err = platform_get_irq_byname(pdev, "msi");
 	if (err < 0) {
 		dev_err(dev, "failed to get IRQ: %d\n", err);
-		goto err;
+		goto free_irq_domain;
 	}
 
 	msi->irq = err;
@@ -1545,17 +1545,35 @@ static int tegra_pcie_msi_setup(struct tegra_pcie *pcie)
 			  tegra_msi_irq_chip.name, pcie);
 	if (err < 0) {
 		dev_err(dev, "failed to request IRQ: %d\n", err);
-		goto err;
+		goto free_irq_domain;
+	}
+
+	/* Though the PCIe controller can address >32-bit address space, to
+	 * facilitate endpoints that support only 32-bit MSI target address,
+	 * the mask is set to 32-bit to make sure that MSI target address is
+	 * always a 32-bit address
+	 */
+	err = dma_set_coherent_mask(dev, DMA_BIT_MASK(32));
+	if (err < 0) {
+		dev_err(dev, "failed to set DMA coherent mask: %d\n", err);
+		goto free_irq;
+	}
+
+	msi->virt = dma_alloc_attrs(dev, PAGE_SIZE, &msi->phys, GFP_KERNEL,
+				    DMA_ATTR_NO_KERNEL_MAPPING);
+	if (!msi->virt) {
+		dev_err(dev, "failed to allocate DMA memory for MSI\n");
+		err = -ENOMEM;
+		goto free_irq;
 	}
 
-	/* setup AFI/FPCI range */
-	msi->pages = __get_free_pages(GFP_KERNEL, 0);
-	msi->phys = virt_to_phys((void *)msi->pages);
 	host->msi = &msi->chip;
 
 	return 0;
 
-err:
+free_irq:
+	free_irq(msi->irq, pcie);
+free_irq_domain:
 	irq_domain_remove(msi->domain);
 	return err;
 }
@@ -1592,7 +1610,8 @@ static void tegra_pcie_msi_teardown(struct tegra_pcie *pcie)
 	struct tegra_msi *msi = &pcie->msi;
 	unsigned int i, irq;
 
-	free_pages(msi->pages, 0);
+	dma_free_attrs(pcie->dev, PAGE_SIZE, msi->virt, msi->phys,
+		       DMA_ATTR_NO_KERNEL_MAPPING);
 
 	if (msi->irq > 0)
 		free_irq(msi->irq, pcie);
-- 
2.17.1