linux-kernel - [PATCH 1/2] firmware: arm_ffa: Explicitly cast return value from FFA

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Message-Id: <20250221095633.506678-1-sudeep.holla@arm.com>
Date: Fri, 21 Feb 2025 09:56:31 +0000
From: Sudeep Holla <sudeep.holla@....com>
To: linux-arm-kernel@...ts.infradead.org
Cc: Sudeep Holla <sudeep.holla@....com>,
	linux-kernel@...r.kernel.org,
	Andrei Homescu <ahomescu@...gle.com>
Subject: [PATCH 1/2] firmware: arm_ffa: Explicitly cast return value from FFA_VERSION before comparison

The return value ver.a0 is unsigned long type and FFA_RET_NOT_SUPPORTED
is a negative value.

Since the return value from the firmware can be just 32-bit even on
64-bit systems as FFA specification mentions it as int32 error code in
w0 register, explicitly casting to s32 ensures correct sign interpretation
when comparing against a signed error code FFA_RET_NOT_SUPPORTED.

Without casting, comparison between unsigned long and a negative
constant could lead to unintended results due to type promotions.

Fixes: 3bbfe9871005 ("firmware: arm_ffa: Add initial Arm FFA driver support")
Reported-by: Andrei Homescu <ahomescu@...gle.com>
Signed-off-by: Sudeep Holla <sudeep.holla@....com>
---
 drivers/firmware/arm_ffa/driver.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/firmware/arm_ffa/driver.c b/drivers/firmware/arm_ffa/driver.c
index 254aa57ddafd..a77bb205ff7d 100644
--- a/drivers/firmware/arm_ffa/driver.c
+++ b/drivers/firmware/arm_ffa/driver.c
@@ -144,7 +144,7 @@ static int ffa_version_check(u32 *version)
 		      .a0 = FFA_VERSION, .a1 = FFA_DRIVER_VERSION,
 		      }, &ver);
 
-	if (ver.a0 == FFA_RET_NOT_SUPPORTED) {
+	if ((s32)ver.a0 == FFA_RET_NOT_SUPPORTED) {
 		pr_info("FFA_VERSION returned not supported\n");
 		return -EOPNOTSUPP;
 	}
-- 
2.34.1