[alsa-devel] Support for getting "manufacturer" from snd_seq_client_info and/or snd_ctl_card_info

Takashi Iwai tiwai at suse.de
Tue May 13 17:00:02 CEST 2014

At Tue, 13 May 2014 11:24:40 +0200,
Clemens Ladisch wrote:
> Adam Goode wrote:
> > On Sun, May 11, 2014 at 12:50 AM, Clemens Ladisch <clemens at ladisch.de> wrote:
> > > Adam Goode wrote:
> > > > I am working on a seq implementation for Chrome, to replace the rawmidi
> > > > implementation. I can retain the manufacturer extraction hack on the card,
> > > > but seq requires yet another hack to guess the card for a particular seq
> > > > client.
> > > >
> > > > A completely different solution would be to add all this info to sysfs
> >
> > > USB devices already have this information in sysfs.
> >
> > This is true. Unfortunately, here are the current steps to get this
> > information:
> > 1. Given a seq client, attempt to guess the card by making assumptions
> >    about client->card numbering.
> > 2. From the card, attempt to guess the manufacturer by making
> >    assumptions about how longname is constructed. Or, attempt to
> >    extract the usb information from the card info struct and then try
> >    to get the info from /sys (but this gives us only the manufacturer
> >    string from usb, not the quirk vendor name that the usb midi driver
> >    knows about).
> >
> > What I would like to do is make these mappings explicit. Because Alsa
> > is very ioctl driven, I was thinking the way to do this is through the
> > existing ioctl API. But since I really just want to expose a lot more
> > read-only info about the system, perhaps files in /sys would be an
> > acceptable way to expose this information.
> The ioctl API (and the library API on top of it) already exists.  Why
> do you want to introduce another kind of API that cannot be used for
> virtual devices?
> > At least, I would like to take the rather detailed information stored
> > in /prod/asound and expose this in a more sysfs way via /sys, then add
> > more fields and info. Does this sound reasonable?
> Almost all the information in /proc/asound is already available through
> some ioctl, and the missing information can be added easily.
> OK, here is my proposal:
> 1. Add the card number to snd_seq_client_info.  (For kernel drivers;
>    user clients might have the PID here while we're at it.)
>    (As long as you are interested only in USB devices, this might be all
>    you need.)
> 2. Add the manufacturer name to snd_ctl_card_info.  For USB devices,
>    this is almost always known, but most other drivers do not know the
>    name of the card manufacturer (as opposed to the chip manufacturer).
>    In those cases, the most informative name that a driver could provide
>    would be based on a registered ID like "USB:0x1234", "PCI:0x5678", or
>    "IEEE:0x9abcde".  (It's possible to look these up in usb.ids, pci.ids,
>    and oui.txt, but I'm not sure if it would be a good idea to let
>    alsa-lib do this lookup.)

This sounds good to me.  It's small enough and least impact to the
existing API.

I'm not opposing to creating /sys entries, though.  But, if we do
exposing to /sys, this has to be done properly.  Namely, the question
isn't only about the sequencer stuff but about all entries in /proc.
So, this won't be a quick task, in anyway.



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