linux-kernel - [PATCH] firmware: cirrus: cs_dsp: Avoid padding bytes in cs_dsp_coeff

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Date:   Mon, 25 Apr 2022 10:51:59 +0100
From:   Richard Fitzgerald <rf@...nsource.cirrus.com>
To:     <broonie@...nel.org>
CC:     <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>,
        <patches@...nsource.cirrus.com>,
        Richard Fitzgerald <rf@...nsource.cirrus.com>
Subject: [PATCH] firmware: cirrus: cs_dsp: Avoid padding bytes in cs_dsp_coeff_ctl

Change the order of members in struct cs_dsp_coeff_ctl to avoid
the compiler having to insert alignment padding bytes. On a x86_64
build this saves 16 bytes per control.

- Pointers are collected to the top of the struct (with the exception of
  priv, as noted below), so that they are inherently aligned.
- The set and enable bitflags are placed together so they can be merged.
- priv is placed at the end of the struct - it is for use by the
  client so it is helpful to make it stand out, and since the compiler
  will always pad the struct size to an alignment multiple putting a
  pointer last won't introduce any more padding.
- struct cs_dsp_alg_region is placed at the end, right before priv, for
  the same reasoning as priv.

Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
---
 include/linux/firmware/cirrus/cs_dsp.h | 28 +++++++++++++-------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/include/linux/firmware/cirrus/cs_dsp.h b/include/linux/firmware/cirrus/cs_dsp.h
index 38b4da3ddfe4..30055706cce2 100644
--- a/include/linux/firmware/cirrus/cs_dsp.h
+++ b/include/linux/firmware/cirrus/cs_dsp.h
@@ -68,36 +68,36 @@ struct cs_dsp_alg_region {
 
 /**
  * struct cs_dsp_coeff_ctl - Describes a coefficient control
+ * @list:		List node for internal use
+ * @dsp:		DSP instance associated with this control
+ * @cache:		Cached value of the control
  * @fw_name:		Name of the firmware
  * @subname:		Name of the control parsed from the WMFW
  * @subname_len:	Length of subname
- * @alg_region:		Logical region associated with this control
- * @dsp:		DSP instance associated with this control
- * @enabled:		Flag indicating whether control is enabled
- * @list:		List node for internal use
- * @cache:		Cached value of the control
  * @offset:		Offset of control within alg_region in words
  * @len:		Length of the cached value in bytes
- * @set:		Flag indicating the value has been written by the user
- * @flags:		Bitfield of WMFW_CTL_FLAG_ control flags defined in wmfw.h
  * @type:		One of the WMFW_CTL_TYPE_ control types defined in wmfw.h
+ * @flags:		Bitfield of WMFW_CTL_FLAG_ control flags defined in wmfw.h
+ * @set:		Flag indicating the value has been written by the user
+ * @enabled:		Flag indicating whether control is enabled
+ * @alg_region:		Logical region associated with this control
  * @priv:		For use by the client
  */
 struct cs_dsp_coeff_ctl {
+	struct list_head list;
+	struct cs_dsp *dsp;
+	void *cache;
 	const char *fw_name;
 	/* Subname is needed to match with firmware */
 	const char *subname;
 	unsigned int subname_len;
-	struct cs_dsp_alg_region alg_region;
-	struct cs_dsp *dsp;
-	unsigned int enabled:1;
-	struct list_head list;
-	void *cache;
 	unsigned int offset;
 	size_t len;
-	unsigned int set:1;
-	unsigned int flags;
 	unsigned int type;
+	unsigned int flags;
+	unsigned int set:1;
+	unsigned int enabled:1;
+	struct cs_dsp_alg_region alg_region;
 
 	void *priv;
 };
-- 
2.30.2