linux-kernel - [PATCH] firmware: arm_scmi: Eliminate local db variable in SCMI_PERF_FC_RING

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Date:   Fri,  9 Aug 2019 21:49:10 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH] firmware: arm_scmi: Eliminate local db variable in SCMI_PERF_FC_RING_DB

clang warns four times:

drivers/firmware/arm_scmi/perf.c:320:24: warning: variable 'db' is
uninitialized when used within its own initialization [-Wuninitialized]
                SCMI_PERF_FC_RING_DB(db, 64);
                ~~~~~~~~~~~~~~~~~~~~~^~~~~~~
drivers/firmware/arm_scmi/perf.c:300:31: note: expanded from macro
'SCMI_PERF_FC_RING_DB'
        struct scmi_fc_db_info *db = doorbell;          \
                                ~~   ^~~~~~~~

This happens because the doorbell identifier becomes db after
preprocessing:

        if (db->width == 1)
                do {
                        u8 val = 0;
                        struct scmi_fc_db_info *db = db;
                        if (db->mask)
                                val = ioread8(db->addr) & db->mask;
                        iowrite8((u8)db->set | val, db->addr);
                } while (0);

We could swap the doorbell and db identifiers within the macro and that
would resolve the issue; however, there doesn't appear to be a good
reason for having two copies of the same variable. Eliminate the one in
the do while loop to prevent this warning and make the code clearer.

Fixes: 8f12cbcb6abc ("firmware: arm_scmi: Make use SCMI v2.0 fastchannel for performance protocol")
Link: https://github.com/ClangBuiltLinux/linux/issues/635
Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
---
 drivers/firmware/arm_scmi/perf.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/firmware/arm_scmi/perf.c b/drivers/firmware/arm_scmi/perf.c
index 2c5201c8354c..ab946ef6b914 100644
--- a/drivers/firmware/arm_scmi/perf.c
+++ b/drivers/firmware/arm_scmi/perf.c
@@ -294,10 +294,9 @@ scmi_perf_describe_levels_get(const struct scmi_handle *handle, u32 domain,
 	return ret;
 }
 
-#define SCMI_PERF_FC_RING_DB(doorbell, w)		\
+#define SCMI_PERF_FC_RING_DB(db, w)			\
 do {							\
 	u##w val = 0;					\
-	struct scmi_fc_db_info *db = doorbell;		\
 							\
 	if (db->mask)					\
 		val = ioread##w(db->addr) & db->mask;	\
-- 
2.23.0.rc2