[Qemu-devel] [PATCH 2/2] arm/virt: Mark pcie controller node as dma-coherent

[Bogdan Purcareata <bogdan.purcareata@nxp.com>]

A PCI device is marked either as coherent or non-coherent based on the pcie
controller "dma-coherent" property. This is further used when configuring the
IOMMU ops for the device DMA resources (e.g. descriptor rings, for e1000e).

This dma-coherent property needs to be configured in the guest environment,
in case there's a directly assigned VFIO PCI device. Since the guest only
receives one emulated pcie controller bus - regardless of the host
configuration - add this property if there's at least one host pcie host
controller that is DMA coherent (this implies that the host interconnect
is coherent as well).

Signed-off-by: Bogdan Purcareata <bogdan.purcareata@nxp.com>
---
 hw/arm/virt.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 371e3a7..b640174 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -867,6 +867,32 @@ static void create_pcie_irq_map(const VirtBoardInfo *vbi, uint32_t gic_phandle,
                            0x7           /* PCI irq */);
 }
 
+static bool is_host_pcie_dma_coherent(void)
+{
+    void *host_fdt;
+    char **node_path;
+    bool ret = false;
+
+    host_fdt = load_device_tree_from_sysfs();
+
+    node_path = qemu_fdt_node_path_prop(host_fdt, "pcie", "dma-coherent",
+            NULL, 0, &error_fatal);
+
+    /* no pcie controllers found on host, therefore non dma-coherent */
+    if (!node_path || !node_path[0]) {
+        goto out;
+    }
+
+    /* for now, if at least one pcie node is dma-coherent,
+     * it is considered that the host is dma-coherent with respect to pcie */
+    ret = true;
+
+out:
+    g_strfreev(node_path);
+    g_free(host_fdt);
+    return ret;
+}
+
 static void create_pcie(const VirtBoardInfo *vbi, qemu_irq *pic,
                         bool use_highmem)
 {
@@ -981,6 +1007,11 @@ static void create_pcie(const VirtBoardInfo *vbi, qemu_irq *pic,
     }
 
     qemu_fdt_setprop_cell(vbi->fdt, nodename, "#interrupt-cells", 1);
+
+    if (is_host_pcie_dma_coherent()) {
+        qemu_fdt_setprop(vbi->fdt, nodename, "dma-coherent", NULL, 0);
+    }
+
     create_pcie_irq_map(vbi, vbi->gic_phandle, irq, nodename);
 
     g_free(nodename);
-- 
1.9.1