Re: [alsa-devel] Idea: dynamic loading of USB quirks

Re: [alsa-devel] Idea: dynamic loading of USB quirks

[Daniel Mack]

[cc lkml as this might be of broader interest]

On 01.11.2012 00:32, maillist@superlative.org wrote:
> Dear Alsa community,
> I've some minor contributions in the form of patches for USB quirks for 
> devices in the past. It occurred to me that having these USB quirks hardcoded 
> into the driver maybe isn't the best thing.
> 
> Looking at the current quirks file, the majority of them are relatively trivial 
> and are really just there to give the USB driver a nudge in the right 
> direction.
> 
> Having to have these hardcoded into the driver creates a number of issues:
> 
> 1. It needs someone with the expertise and will, and access the specific device 
> for testing, to build the quirk. To hardened ALSA hackers this seems trivial, 
> but to an average end user who has a device they want to get supported, this 
> can be pretty inpenatrable. The complexity of just getting the alsa source 
> installed and set up for compilation is enough to put off the vast majority of 
> users.
> 
> 2. It makes the process of getting the driver "to market" lengthy as these 
> changes have to go through all of the normal release schedules, and these are 
> pretty opaque.
> 
> 3. It makes getting changing a driver (because of a bug, or a new release of 
> hardware) difficult as the revisions need to go through the whole process of 
> creating a patch, getting it accepted, and then the long kernel release 
> process, as well as the various distribution release processes.
> 
> It occured to me that there might be a better way where quirks like this could 
> be dynamically loaded into the driver after it has loaded. This would a 
> structured text file describing the quirk to be created and pushed into the 
> driver. Ultimately this could be wrapped into a framework where quirk files 
> could be put into a common directory (similar to modprobe.d) with a startup 
> script which pushed these into the driver.

The idea is interesting, but we would need to find a way to not only
cover the entries in quirks-list.h but the other hard-coded details as well.

I fear that if quirk fixups are done on both the kernel level and loaded
from userspace, it actually makes debugging and maintainance harder.

Then again, if a versatile and clean solution to this problem is found,
there would be tons of other drivers in Linux to benefit from it, just
think about the hda driver to begin with. But not only in the ALSA area.


Daniel

Re: [alsa-devel] Idea: dynamic loading of USB quirks

[maillist]

On Thursday 01 Nov 2012 10:05:41 Daniel Mack wrote:
> [cc lkml as this might be of broader interest]
> 

> 
> Then again, if a versatile and clean solution to this problem is found,
> there would be tons of other drivers in Linux to benefit from it, just
> think about the hda driver to begin with. But not only in the ALSA area.
>

I was initially thinking of the more trivial USB quirkes only, and having the 
more complex quirks remain as hard coded.

But it does make sense that, if such a capability could be extended, that it 
could be used for other drivers too.

Cheers,

Keith

Re: [alsa-devel] Idea: dynamic loading of USB quirks

[Takashi Iwai]

At Thu, 01 Nov 2012 10:05:41 +0100,
Daniel Mack wrote:
> 
> [cc lkml as this might be of broader interest]
> 
> On 01.11.2012 00:32, maillist@superlative.org wrote:
> > Dear Alsa community,
> > I've some minor contributions in the form of patches for USB quirks for 
> > devices in the past. It occurred to me that having these USB quirks hardcoded 
> > into the driver maybe isn't the best thing.
> > 
> > Looking at the current quirks file, the majority of them are relatively trivial 
> > and are really just there to give the USB driver a nudge in the right 
> > direction.
> > 
> > Having to have these hardcoded into the driver creates a number of issues:
> > 
> > 1. It needs someone with the expertise and will, and access the specific device 
> > for testing, to build the quirk. To hardened ALSA hackers this seems trivial, 
> > but to an average end user who has a device they want to get supported, this 
> > can be pretty inpenatrable. The complexity of just getting the alsa source 
> > installed and set up for compilation is enough to put off the vast majority of 
> > users.
> > 
> > 2. It makes the process of getting the driver "to market" lengthy as these 
> > changes have to go through all of the normal release schedules, and these are 
> > pretty opaque.
> > 
> > 3. It makes getting changing a driver (because of a bug, or a new release of 
> > hardware) difficult as the revisions need to go through the whole process of 
> > creating a patch, getting it accepted, and then the long kernel release 
> > process, as well as the various distribution release processes.
> > 
> > It occured to me that there might be a better way where quirks like this could 
> > be dynamically loaded into the driver after it has loaded. This would a 
> > structured text file describing the quirk to be created and pushed into the 
> > driver. Ultimately this could be wrapped into a framework where quirk files 
> > could be put into a common directory (similar to modprobe.d) with a startup 
> > script which pushed these into the driver.
> 
> The idea is interesting, but we would need to find a way to not only
> cover the entries in quirks-list.h but the other hard-coded details as well.
> 
> I fear that if quirk fixups are done on both the kernel level and loaded
> from userspace, it actually makes debugging and maintainance harder.
> 
> Then again, if a versatile and clean solution to this problem is found,
> there would be tons of other drivers in Linux to benefit from it, just
> think about the hda driver to begin with. But not only in the ALSA area.

HD-audio driver has already a sort of "firmware" support.  It can read
text data to patch the pre-existing BIOS setup, add extra
initialization verbs or give hints for drivers to change the specific
behavior.

For USB-audio, a simple TLV representation would be feasible for an
extra quirk entry.


Takashi