[PATCH] firmware: cirrus: cs_dsp: Avoid padding bytes in cs_dsp_coeff_ctl

[PATCH] firmware: cirrus: cs_dsp: Avoid padding bytes in cs_dsp_coeff_ctl

[Richard Fitzgerald]

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@opensource.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

Re: [PATCH] firmware: cirrus: cs_dsp: Avoid padding bytes in cs_dsp_coeff_ctl

[Charles Keepax]

On Mon, Apr 25, 2022 at 10:51:59AM +0100, Richard Fitzgerald wrote:
> 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@opensource.cirrus.com>
> ---

Reviewed-by: Charles Keepax <ckeepax@opensource.cirrus.com>

Thanks,
Charles

Re: [PATCH] firmware: cirrus: cs_dsp: Avoid padding bytes in cs_dsp_coeff_ctl

[Mark Brown]

On Mon, 25 Apr 2022 10:51:59 +0100, Richard Fitzgerald wrote:
> 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.
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git for-next

Thanks!

[1/1] firmware: cirrus: cs_dsp: Avoid padding bytes in cs_dsp_coeff_ctl
      commit: 430c3500995484962bdbccf358201afef8055535

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark