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