[RESEND PATCH v4 04/11] perf/cxl: Accept an overflow interrupt on MSI message number 0

cxl_pmu_probe() rejects the PMU when info->irq <= 0, but at that point the
field still holds the MSI/MSI-X message number the device signals overflow
on, not a Linux virq. That number is 0-based, and -1 means no interrupt
support. Message number 0 is valid and pci_irq_vector() takes a 0-based
index, so a compliant device signalling on the first vector fails to probe.

Reject only the no-interrupt case, matching how the CXL mailbox and event
interrupts handle it.

Fixes: 5d7107c72796 ("perf: CXL Performance Monitoring Unit driver")
Reported-by: sashiko-bot@kernel.org
Closes: https://sashiko.dev/#/patchset/20260715191454.459673-1-dave@stgolabs.net?part=1
Assisted-by: Claude:claude-opus-4-8
Reviewed-by: Jonathan Cameron <redacted>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Acked-by: Richard Cheng <redacted>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
---
v4:
- Move ahead of the info->msi_vec rename so this one-liner stands alone for
  backporting (Robin).
---
 drivers/perf/cxl_pmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/perf/cxl_pmu.c b/drivers/perf/cxl_pmu.c
index 40741e529d9b..2bebbbe67a0a 100644
--- a/drivers/perf/cxl_pmu.c
+++ b/drivers/perf/cxl_pmu.c

@@ -873,7 +873,7 @@ static int cxl_pmu_probe(struct device *dev)
 		.capabilities = PERF_PMU_CAP_NO_EXCLUDE,
 	};
 
-	if (info->irq <= 0)
+	if (info->irq < 0)
 		return -EINVAL;
 
 	rc = pci_irq_vector(pdev, info->irq);

-- 
2.54.0