[RFC PATCH 4/6] ALSA: mixer_audient: Fill the cache on first use

[Will Porter <mrwillporter@gmail.com>]

The probe reads every channel of a cached control. That is not
necessary: a get or put of a channel whose cache bit is clear already
reads the device and fills the cache.

Remove the probe read of cached controls. A failed first read returns
its error to the caller and leaves the cache bit clear, so the next
call reads again.

This changes behaviour. The probe sends no GET for a cached control:
that is 12 fewer requests on the EVO4 and 56 fewer on the iD14 MkI. A
failed read no longer logs "cannot read channel" at probe. A put to a
channel whose cache bit is clear first sends a GET, then sends a SET
only if the value differs.

The probe write of the init value of write-only controls stays.

Assisted-by: Claude:claude-fable-5-2
Assisted-by: Claude:claude-sonnet-5-5
Signed-off-by: Will Porter <mrwillporter@gmail.com>
---
 sound/usb/mixer_audient.c | 22 ++++------------------
 1 file changed, 4 insertions(+), 18 deletions(-)

diff --git a/sound/usb/mixer_audient.c b/sound/usb/mixer_audient.c
index 1bc6b4bbd2910..ff7bf518743ee 100644
--- a/sound/usb/mixer_audient.c
+++ b/sound/usb/mixer_audient.c
@@ -1091,10 +1091,10 @@ static int snd_audient_add_ctrl(struct usb_mixer_interface *mixer,
 		elem->get_cur_broken = 1;
 
 	/*
-	 * A failed probe transfer must not fail the card: warn and keep the
-	 * control. Its cache bit stays clear, so a cached control reads the
-	 * device again on its next get, and a write-only control shows an
-	 * unknown value until a put succeeds.
+	 * A cached control reads the device on its first get or put. A
+	 * write-only control is written once at probe. A failed probe write
+	 * must not fail the card: warn and keep the control. Its cache bit
+	 * stays clear, so it shows an unknown value until a put succeeds.
 	 */
 	if (ctype->access == SND_AUDIENT_ACCESS_WRITE_ONLY) {
 		int i;
@@ -1108,20 +1108,6 @@ static int snd_audient_add_ctrl(struct usb_mixer_interface *mixer,
 					       "%s: cannot set channel %d (%d)\n",
 					       ctrl->name, i, ret);
 		}
-	} else if (ctype->access == SND_AUDIENT_ACCESS_CACHED) {
-		int i;
-
-		for (i = 0; i < ctrl->hwchannels; i++) {
-			u32 val;
-
-			ret = snd_audient_raw_get_one(elem, ctype, i,
-						      ctrl->val_offs + i,
-						      &val);
-			if (ret < 0)
-				usb_audio_warn(mixer->chip,
-					       "%s: cannot read channel %d (%d)\n",
-					       ctrl->name, i, ret);
-		}
 	}
 
 	kctl = snd_ctl_new1(&knew, elem);
-- 
2.47.3