misc: pci_endpoint_test: Add support for capabilities

The test BAR is on the EP side is allocated using pci_epf_alloc_space(),
which allocates the backing memory using dma_alloc_coherent(), which will
return zeroed memory regardless of __GFP_ZERO was set or not.

This means that running a new version of pci-endpoint-test.c (host side)
with an old version of pci-epf-test.c (EP side) will not see any
capabilities being set (as intended), so this is backwards compatible.

Additionally, the EP side always allocates at least 128 bytes for the test
BAR (excluding the MSI-X table), this means that adding another register at
offset 0x30 is still within the 128 available bytes.

For now, we only add the CAP_UNALIGNED_ACCESS capability.

If CAP_UNALIGNED_ACCESS is set, that means that the EP side supports
reading/writing to an address without any alignment requirements.

Thus, if CAP_UNALIGNED_ACCESS is set, make sure that the host side does
not add any extra padding to the buffers that we allocate (which was only
done in order to get the buffers to satisfy certain alignment requirements
by the endpoint controller).

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Niklas Cassel <[email protected]>
Signed-off-by: Krzysztof Wilczyński <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
Reviewed-by: Manivannan Sadhasivam <[email protected]>
Reviewed-by: Frank Li <[email protected]>

Author: floatious

drivers/misc/pci_endpoint_test.c

@@ -69,6 +69,9 @@
 #define PCI_ENDPOINT_TEST_FLAGS			0x2c
 #define FLAG_USE_DMA				BIT(0)
 
+#define PCI_ENDPOINT_TEST_CAPS			0x30
+#define CAP_UNALIGNED_ACCESS			BIT(0)
+
 #define PCI_DEVICE_ID_TI_AM654			0xb00c
 #define PCI_DEVICE_ID_TI_J7200			0xb00f
 #define PCI_DEVICE_ID_TI_AM64			0xb010
@@ -805,6 +808,20 @@ static const struct file_operations pci_endpoint_test_fops = {
 	.unlocked_ioctl = pci_endpoint_test_ioctl,
 };
 
+static void pci_endpoint_test_get_capabilities(struct pci_endpoint_test *test)
+{
+	struct pci_dev *pdev = test->pdev;
+	struct device *dev = &pdev->dev;
+	u32 caps;
+
+	caps = pci_endpoint_test_readl(test, PCI_ENDPOINT_TEST_CAPS);
+	dev_dbg(dev, "PCI_ENDPOINT_TEST_CAPS: %#x\n", caps);
+
+	/* CAP_UNALIGNED_ACCESS is set if the EP can do unaligned access */
+	if (caps & CAP_UNALIGNED_ACCESS)
+		test->alignment = 0;
+}
+
 static int pci_endpoint_test_probe(struct pci_dev *pdev,
 				   const struct pci_device_id *ent)
 {
@@ -906,6 +923,8 @@ static int pci_endpoint_test_probe(struct pci_dev *pdev,
 		goto err_kfree_test_name;
 	}
 
+	pci_endpoint_test_get_capabilities(test);
+
 	misc_device = &test->miscdev;
 	misc_device->minor = MISC_DYNAMIC_MINOR;
 	misc_device->name = kstrdup(name, GFP_KERNEL);