[PATCH] virt-pci: add platform bus support

[Vincent Whitchurch]

This driver registers PCI busses, but the underlying virtio protocol
could just as easily be used to provide a platform bus instead.  If the
virtio device node in the devicetree indicates that it's compatible with
simple-bus, register platform devices instead of handling it as a PCI
bus.

Only one platform bus is allowed and the logic MMIO region for the
platform bus is placed at an arbitrarily-chosen address away from the
PCI region.

Signed-off-by: Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>
---
My first approach to getting platform drivers working on UML was by
adding a minimal PCI-to-platform bridge driver, which worked without
modifications to virt-pci, but that got shot down:

 https://lore.kernel.org/lkml/20230120-simple-mfd-pci-v1-1-c46b3d6601ef@xxxxxxxx/
---
 arch/um/drivers/virt-pci.c | 91 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 91 insertions(+)

diff --git a/arch/um/drivers/virt-pci.c b/arch/um/drivers/virt-pci.c
index 3ac220dafec4..0ff69d6ad253 100644
--- a/arch/um/drivers/virt-pci.c
+++ b/arch/um/drivers/virt-pci.c
@@ -8,6 +8,7 @@
 #include <linux/virtio.h>
 #include <linux/virtio_config.h>
 #include <linux/logic_iomem.h>
+#include <linux/of_platform.h>
 #include <linux/irqdomain.h>
 #include <linux/virtio_pcidev.h>
 #include <linux/virtio-uml.h>
@@ -39,6 +40,8 @@ struct um_pci_device {
 	unsigned long status;
 
 	int irq;
+
+	bool platform;
 };
 
 struct um_pci_device_reg {
@@ -48,6 +51,7 @@ struct um_pci_device_reg {
 
 static struct pci_host_bridge *bridge;
 static DEFINE_MUTEX(um_pci_mtx);
+static struct um_pci_device *um_pci_platform_device;
 static struct um_pci_device_reg um_pci_devices[MAX_DEVICES];
 static struct fwnode_handle *um_pci_fwnode;
 static struct irq_domain *um_pci_inner_domain;
@@ -480,6 +484,9 @@ static void um_pci_handle_irq_message(struct virtqueue *vq,
 	struct virtio_device *vdev = vq->vdev;
 	struct um_pci_device *dev = vdev->priv;
 
+	if (!dev->irq)
+		return;
+
 	/* we should properly chain interrupts, but on ARCH=um we don't care */
 
 	switch (msg->op) {
@@ -561,6 +568,55 @@ static int um_pci_init_vqs(struct um_pci_device *dev)
 	return 0;
 }
 
+static void __um_pci_virtio_platform_remove(struct virtio_device *vdev,
+					    struct um_pci_device *dev)
+{
+	virtio_reset_device(vdev);
+	vdev->config->del_vqs(vdev);
+
+	mutex_lock(&um_pci_mtx);
+	um_pci_platform_device = NULL;
+	mutex_unlock(&um_pci_mtx);
+
+	kfree(dev);
+}
+
+static int um_pci_virtio_platform_probe(struct virtio_device *vdev,
+					struct um_pci_device *dev)
+{
+	int ret;
+
+	dev->platform = true;
+
+	mutex_lock(&um_pci_mtx);
+
+	if (um_pci_platform_device) {
+		mutex_unlock(&um_pci_mtx);
+		ret = -EBUSY;
+		goto out_free;
+	}
+
+	ret = um_pci_init_vqs(dev);
+	if (ret) {
+		mutex_unlock(&um_pci_mtx);
+		goto out_free;
+	}
+
+	um_pci_platform_device = dev;
+
+	mutex_unlock(&um_pci_mtx);
+
+	ret = of_platform_default_populate(vdev->dev.of_node, NULL, &vdev->dev);
+	if (ret)
+		__um_pci_virtio_platform_remove(vdev, dev);
+
+	return ret;
+
+out_free:
+	kfree(dev);
+	return ret;
+}
+
 static int um_pci_virtio_probe(struct virtio_device *vdev)
 {
 	struct um_pci_device *dev;
@@ -574,6 +630,9 @@ static int um_pci_virtio_probe(struct virtio_device *vdev)
 	dev->vdev = vdev;
 	vdev->priv = dev;
 
+	if (of_device_is_compatible(vdev->dev.of_node, "simple-bus"))
+		return um_pci_virtio_platform_probe(vdev, dev);
+
 	mutex_lock(&um_pci_mtx);
 	for (i = 0; i < MAX_DEVICES; i++) {
 		if (um_pci_devices[i].dev)
@@ -623,6 +682,12 @@ static void um_pci_virtio_remove(struct virtio_device *vdev)
 	struct um_pci_device *dev = vdev->priv;
 	int i;
 
+	if (dev->platform) {
+		of_platform_depopulate(&vdev->dev);
+		__um_pci_virtio_platform_remove(vdev, dev);
+		return;
+	}
+
         /* Stop all virtqueues */
         virtio_reset_device(vdev);
         vdev->config->del_vqs(vdev);
@@ -860,6 +925,30 @@ void *pci_root_bus_fwnode(struct pci_bus *bus)
 	return um_pci_fwnode;
 }
 
+static long um_pci_map_platform(unsigned long offset, size_t size,
+				const struct logic_iomem_ops **ops,
+				void **priv)
+{
+	if (!um_pci_platform_device)
+		return -ENOENT;
+
+	*ops = &um_pci_device_bar_ops;
+	*priv = &um_pci_platform_device->resptr[0];
+
+	return 0;
+}
+
+static const struct logic_iomem_region_ops um_pci_platform_ops = {
+	.map = um_pci_map_platform,
+};
+
+static struct resource virt_platform_resource = {
+	.name = "platform",
+	.start = 0x10000000,
+	.end = 0x1fffffff,
+	.flags = IORESOURCE_MEM,
+};
+
 static int __init um_pci_init(void)
 {
 	int err, i;
@@ -868,6 +957,8 @@ static int __init um_pci_init(void)
 				       &um_pci_cfgspace_ops));
 	WARN_ON(logic_iomem_add_region(&virt_iomem_resource,
 				       &um_pci_iomem_ops));
+	WARN_ON(logic_iomem_add_region(&virt_platform_resource,
+				       &um_pci_platform_ops));
 
 	if (WARN(CONFIG_UML_PCI_OVER_VIRTIO_DEVICE_ID < 0,
 		 "No virtio device ID configured for PCI - no PCI support\n"))

---
base-commit: 1b929c02afd37871d5afb9d498426f83432e71c2
change-id: 20230127-uml-pci-platform-ef851ba75f80

Best regards,
-- 
Vincent Whitchurch <vincent.whitchurch@xxxxxxxx>