[PATCH 2/2] misc: pci_endpoint_test: Improve logic to check status for doorbell test case

[Niklas Cassel <cassel@kernel.org>]

The EPF driver drivers/pci/endpoint/functions/pci-epf-test.c
only sets STATUS_DOORBELL_ENABLE_SUCCESS as the final step in
pci_epf_test_enable_doorbell()

Likewise it only sets STATUS_DOORBELL_DISABLE_SUCCESS as the final step in
pci_epf_test_disable_doorbell().

The safest way is therefore to check if the SUCCESS bit was set,
not to check if the FAIL bit was set.

Because, during a wait_for_completion_timeout() timeout, if we did not
receive an IRQ, obviously the FAIL bit will not be set.

For the STATUS_DOORBELL_ENABLE case, the if-statement also fails if there
was a timeout ('left' == 0). However, we've seen an issue where a buggy EPC
driver was sending two IRQs in response to a single DOORBELL_ENABLE
command, and in this case the second wait_for_completion() will return
immediately (i.e. no timeout - 'left' != zero) and the SUCCESS bit will not
be set. Thus, the safest way is to simply check if the SUCCESS bit is set.

Signed-off-by: Niklas Cassel <cassel@kernel.org>
---
 drivers/misc/pci_endpoint_test.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/misc/pci_endpoint_test.c b/drivers/misc/pci_endpoint_test.c
index 26ab9252251f..1019bcd0628f 100644
--- a/drivers/misc/pci_endpoint_test.c
+++ b/drivers/misc/pci_endpoint_test.c
@@ -1094,7 +1094,7 @@ static int pci_endpoint_test_doorbell(struct pci_endpoint_test *test)
 	left = wait_for_completion_timeout(&test->irq_raised, msecs_to_jiffies(1000));
 
 	status = pci_endpoint_test_readl(test, PCI_ENDPOINT_TEST_STATUS);
-	if (!left || (status & STATUS_DOORBELL_ENABLE_FAIL)) {
+	if (!left || !(status & STATUS_DOORBELL_ENABLE_SUCCESS)) {
 		dev_err(dev, "Failed to enable doorbell\n");
 		return -EINVAL;
 	}
@@ -1133,7 +1133,7 @@ static int pci_endpoint_test_doorbell(struct pci_endpoint_test *test)
 
 	status |= pci_endpoint_test_readl(test, PCI_ENDPOINT_TEST_STATUS);
 
-	if (status & STATUS_DOORBELL_DISABLE_FAIL) {
+	if (!(status & STATUS_DOORBELL_DISABLE_SUCCESS)) {
 		dev_err(dev, "Failed to disable doorbell\n");
 		return -EINVAL;
 	}
-- 
2.55.0