selftests: pci_endpoint: Add doorbell test case

Add doorbell test case.

Signed-off-by: Frank Li <Frank.Li@nxp.com>
[mani: Reworded the testcase description]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Tested-by: Niklas Cassel <cassel@kernel.org>
Link: https://patch.msgid.link/20250710-ep-msi-v21-8-57683fc7fb25@nxp.com

Author: nxpfrankli

Documentation/PCI/endpoint/pci-test-howto.rst

@@ -203,3 +203,18 @@ controllers, it is advisable to skip this testcase using this
 command::
 
 	# pci_endpoint_test -f pci_ep_bar -f pci_ep_basic -v memcpy -T COPY_TEST -v dma
+
+Kselftest EP Doorbell
+~~~~~~~~~~~~~~~~~~~~~
+
+If the Endpoint MSI controller is used for the doorbell usecase, run below
+command for testing it:
+
+	# pci_endpoint_test -f pcie_ep_doorbell
+
+	# Starting 1 tests from 1 test cases.
+	#  RUN           pcie_ep_doorbell.DOORBELL_TEST ...
+	#            OK  pcie_ep_doorbell.DOORBELL_TEST
+	ok 1 pcie_ep_doorbell.DOORBELL_TEST
+	# PASSED: 1 / 1 tests passed.
+	# Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0

tools/testing/selftests/pci_endpoint/pci_endpoint_test.c

@@ -229,4 +229,32 @@ TEST_F(pci_ep_data_transfer, COPY_TEST)
 					 test_size[i]);
 	}
 }
+
+FIXTURE(pcie_ep_doorbell)
+{
+	int fd;
+};
+
+FIXTURE_SETUP(pcie_ep_doorbell)
+{
+	self->fd = open(test_device, O_RDWR);
+
+	ASSERT_NE(-1, self->fd) TH_LOG("Can't open PCI Endpoint Test device");
+};
+
+FIXTURE_TEARDOWN(pcie_ep_doorbell)
+{
+	close(self->fd);
+};
+
+TEST_F(pcie_ep_doorbell, DOORBELL_TEST)
+{
+	int ret;
+
+	pci_ep_ioctl(PCITEST_SET_IRQTYPE, PCITEST_IRQ_TYPE_AUTO);
+	ASSERT_EQ(0, ret) TH_LOG("Can't set AUTO IRQ type");
+
+	pci_ep_ioctl(PCITEST_DOORBELL, 0);
+	EXPECT_FALSE(ret) TH_LOG("Test failed for Doorbell\n");
+}
 TEST_HARNESS_MAIN