[PATCH v5 16/17] misc: pci_endpoint_test: Do not write status in IRQ handler

[Damien Le Moal <dlemoal@kernel.org>]

pci_endpoint_test_irqhandler() always rewrites the status register when
an IRQ is raised, either as-is if STATUS_IRQ_RAISED is not set, or with
STATUS_IRQ_RAISED cleared if that flag is set. The first case creates a
race window with the endpoint side, meaning that the host side test
driver may end up reading what it just wrote, thus losing the real
status as set by the endpoint side before raising the next interrupt.
This can prevent detecting that the STATUS_IRQ_RAISED flag was set by
the endpoint.

Remove this race window by not clearing the STATUS_IRQ_RAISED status
flag and not rewriting that register for every IRQ received.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
---
 drivers/misc/pci_endpoint_test.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/misc/pci_endpoint_test.c b/drivers/misc/pci_endpoint_test.c
index 24efe3b88a1f..afd2577261f8 100644
--- a/drivers/misc/pci_endpoint_test.c
+++ b/drivers/misc/pci_endpoint_test.c
@@ -159,10 +159,7 @@ static irqreturn_t pci_endpoint_test_irqhandler(int irq, void *dev_id)
 	if (reg & STATUS_IRQ_RAISED) {
 		test->last_irq = irq;
 		complete(&test->irq_raised);
-		reg &= ~STATUS_IRQ_RAISED;
 	}
-	pci_endpoint_test_writel(test, PCI_ENDPOINT_TEST_STATUS,
-				 reg);
 
 	return IRQ_HANDLED;
 }
-- 
2.39.2