On 21.09.2018 11:43, Takashi Iwai wrote:
On Fri, 21 Sep 2018 10:35:49 +0200,
Jussi Laako wrote:
The caching is currently enabled for all elements, but changing it
should be trivial. The patch below adds is_volatile flag to the
element, and you can set it to true in the quirk somehow for uncached
controls.
This patch looks good and what I need! When trying to figure out where
it is safe to set the volatile flag I thought that I could set it
transparently in add_single_ctl_with_resume() in mixer_quirks.c based
on the SNDRV_CTL_ELEM_ACCESS_VOLATILE flag in provided
snd_kcontrol_new access-member. However, add_single_ctl_with_resume()
is allocating just size of usb_mixer_elem_list unlike
snd_create_std_mono_ctl_offset() which in turn is allocating full
usb_mixer_elem_info size. However, the mixer code seems to be assuming
that the item is always usb_mixer_elem_info instead of just list
header item. Is this allocation behavior correct and is the item
turned into usb_mixer_elem_info somewhere, or is this some kind of
bug? So can I safely turn the allocation in
add_single_ctl_with_resume() into zero initialized usb_mixer_elem_info
instead and set the flag there while keeping correct behavior, or am I
missing something?
We can check SNDRV_CTL_ELEM_ACCESS_VOLATILE instead of introducing a
new flag like my patch, yes. It's just a matter of easiness.
Since there is no link from usb_mixer_elem_info to the assigned
snd_kcontorl, we'd need to add an extra argument in the call path to
inform about the volatileness, and it may become messy. We'll find
the simplest way.
And, IMO, it'd be better to check the cache behavior at setting, since
the cache may be accessed via multiple paths (at reading each element
and at resuming the whole system). But it's no requirement, either.
I have tried with attached patch, on top of your patch, but I'm still
getting cached values from libasound2. It didn't break anything
either... However, I don't see a link between this cache behavior and
specific user space mixer descriptor. Because polling the mixer element
with snd_mixer_selem_get_capture_volume() keeps always returning the
same value. While in parallel checking the value by running "amixer"
from command line gives updated correct value... So is there a second
layer of cache somewhere in libasound2 to explain this discrepancy?
Because one process sees updated value while other one doesn't.
Difference being that the ALSA descriptors are closed and reopened every
time "amixer" is run...
What is more perplexing is that from HDSPe driver same use case works,
but it could be due to some event trigger from the HDSPe driver based on
interrupt?
- Jussi
diff --git a/sound/usb/mixer_quirks.c b/sound/usb/mixer_quirks.c
index 762c190..cff31ce 100644
--- a/sound/usb/mixer_quirks.c
+++ b/sound/usb/mixer_quirks.c
@@ -152,20 +152,24 @@ static int add_single_ctl_with_resume(struct usb_mixer_interface *mixer,
const struct snd_kcontrol_new *knew,
struct usb_mixer_elem_list **listp)
{
+ struct usb_mixer_elem_info *cval;
struct usb_mixer_elem_list *list;
struct snd_kcontrol *kctl;
- list = kzalloc(sizeof(*list), GFP_KERNEL);
- if (!list)
+ cval = kzalloc(sizeof(*cval), GFP_KERNEL);
+ if (!cval)
return -ENOMEM;
+ list = &cval->head;
if (listp)
*listp = list;
+ if (knew->access & SNDRV_CTL_ELEM_ACCESS_VOLATILE)
+ cval->is_volatile = 1;
list->mixer = mixer;
list->id = id;
list->resume = resume;
- kctl = snd_ctl_new1(knew, list);
+ kctl = snd_ctl_new1(knew, cval);
if (!kctl) {
- kfree(list);
+ kfree(cval);
return -ENOMEM;
}
kctl->private_free = snd_usb_mixer_elem_free;
_______________________________________________
Alsa-devel mailing list
Alsa-devel@xxxxxxxxxxxxxxxx
http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
