[Linux-kernel-mentees] [PATCH v4 01/12] IB/hfi1: Check if pcie_capability_read_*() reads ~0

Saheed O. Bolarinwa refactormyself at gmail.com
Fri Jul 31 11:02:29 UTC 2020


On failure pcie_capability_read_dword() sets it's last parameter,
val to 0. In this case dn and up will be 0, so aspm_hw_l1_supported()
will return false.
However, with Patch 12/12, it is possible that val is set to ~0 on
failure. This would introduce a bug because (x & x) == (~0 & x). So
with dn and up being 0x02, a true value is return when the read has
actually failed.

Since, the value ~0 is invalid here,

Reset dn and up to 0 when a value of ~0 is read into them, this
ensures false is returned on failure in this case.

Suggested-by: Bjorn Helgaas <bjorn at helgaas.com>
Signed-off-by: Saheed O. Bolarinwa <refactormyself at gmail.com>
---

 drivers/infiniband/hw/hfi1/aspm.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/infiniband/hw/hfi1/aspm.c b/drivers/infiniband/hw/hfi1/aspm.c
index a3c53be4072c..9605b2145d19 100644
--- a/drivers/infiniband/hw/hfi1/aspm.c
+++ b/drivers/infiniband/hw/hfi1/aspm.c
@@ -33,13 +33,13 @@ static bool aspm_hw_l1_supported(struct hfi1_devdata *dd)
 		return false;
 
 	pcie_capability_read_dword(dd->pcidev, PCI_EXP_LNKCAP, &dn);
-	dn = ASPM_L1_SUPPORTED(dn);
+	dn = (dn == (u32)~0) ? 0 : ASPM_L1_SUPPORTED(dn);
 
 	pcie_capability_read_dword(parent, PCI_EXP_LNKCAP, &up);
-	up = ASPM_L1_SUPPORTED(up);
+	up = (up == (u32)~0) ? 0 : ASPM_L1_SUPPORTED(up);
 
 	/* ASPM works on A-step but is reported as not supported */
-	return (!!dn || is_ax(dd)) && !!up;
+	return (dn || is_ax(dd)) && up;
 }
 
 /* Set L1 entrance latency for slower entry to L1 */
-- 
2.18.4



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