linux-kernel - [PATCH v2] soundwire: bandwidth allocation: Use hweight32() to calculate set bits

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Date:   Wed, 15 Mar 2023 14:50:51 +0000
From:   Richard Fitzgerald <rf@...nsource.cirrus.com>
To:     <vkoul@...nel.org>
CC:     <yung-chuan.liao@...ux.intel.com>,
        <pierre-louis.bossart@...ux.intel.com>, <sanyog.r.kale@...el.com>,
        <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>,
        <patches@...nsource.cirrus.com>,
        Richard Fitzgerald <rf@...nsource.cirrus.com>
Subject: [PATCH v2] soundwire: bandwidth allocation: Use hweight32() to calculate set bits

Replace the call to sdw_ch_mask_to_ch() with a call to hweight32().

sdw_ch_mask_to_ch() is counting the number of set bits. The hweight()
family of functions already do this, and they have an advantage of
using a bit-counting instruction if it is available on the target CPU.
This also fixes a potential infinite loop bug in the implementation of
sdw_ch_mask_to_ch().

Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
---
 drivers/soundwire/bus.h                          | 11 -----------
 drivers/soundwire/generic_bandwidth_allocation.c |  3 ++-
 2 files changed, 2 insertions(+), 12 deletions(-)

diff --git a/drivers/soundwire/bus.h b/drivers/soundwire/bus.h
index 7631ef5e71fb..4ce8d708a39c 100644
--- a/drivers/soundwire/bus.h
+++ b/drivers/soundwire/bus.h
@@ -159,17 +159,6 @@ int sdw_transfer_defer(struct sdw_bus *bus, struct sdw_msg *msg,
 int sdw_fill_msg(struct sdw_msg *msg, struct sdw_slave *slave,
 		 u32 addr, size_t count, u16 dev_num, u8 flags, u8 *buf);
 
-/* Retrieve and return channel count from channel mask */
-static inline int sdw_ch_mask_to_ch(int ch_mask)
-{
-	int c = 0;
-
-	for (c = 0; ch_mask; ch_mask >>= 1)
-		c += ch_mask & 1;
-
-	return c;
-}
-
 /* Fill transport parameter data structure */
 static inline void sdw_fill_xport_params(struct sdw_transport_params *params,
 					 int port_num, bool grp_ctrl_valid,
diff --git a/drivers/soundwire/generic_bandwidth_allocation.c b/drivers/soundwire/generic_bandwidth_allocation.c
index f7c66083a4dd..ea3e8ef408e4 100644
--- a/drivers/soundwire/generic_bandwidth_allocation.c
+++ b/drivers/soundwire/generic_bandwidth_allocation.c
@@ -6,6 +6,7 @@
  *
  */
 
+#include <linux/bitops.h>
 #include <linux/device.h>
 #include <linux/module.h>
 #include <linux/mod_devicetable.h>
@@ -54,7 +55,7 @@ static void sdw_compute_slave_ports(struct sdw_master_runtime *m_rt,
 		slave_total_ch = 0;
 
 		list_for_each_entry(p_rt, &s_rt->port_list, port_node) {
-			ch = sdw_ch_mask_to_ch(p_rt->ch_mask);
+			ch = hweight32(p_rt->ch_mask);
 
 			sdw_fill_xport_params(&p_rt->transport_params,
 					      p_rt->num, false,
-- 
2.30.2