Re: [PATCH v2 4/8] ASoC: topology: ABI - Add name element to snd_soc_tplg_stream

[Takashi Iwai <tiwai@suse.de>]

On Wed, 07 Oct 2015 11:48:37 +0200,
Lin, Mengdong wrote:
> 
> > -----Original Message-----
> > From: Mark Brown [mailto:broonie@kernel.org]
> > Sent: Wednesday, October 07, 2015 1:37 AM
> > To: Lars-Peter Clausen
> > Cc: Koul, Vinod; alsa-devel@alsa-project.org; tiwai@suse.de; Lin, Mengdong;
> > liam.r.girdwood@linux.intel.com; Kp, Jeeja; Prusty, Subhransu S; Patel,
> > Vedang
> > Subject: Re: [alsa-devel] [PATCH v2 4/8] ASoC: topology: ABI - Add name
> > element to snd_soc_tplg_stream
> > 
> > On Tue, Oct 06, 2015 at 06:35:28PM +0200, Lars-Peter Clausen wrote:
> > > On 10/06/2015 06:25 PM, Mark Brown wrote:
> > 
> > > > The problem isn't detecting the error, the point is that if someone
> > > > upgrades their kernel and someone changed the DAI link name then
> > > > their existing userspace will break.  We don't want that error to be
> > > > there to be detected in the first place.
> > 
> > > Another thing to consider is that the topology firmware might be
> > > developed against a non-upstream driver. And in order for the driver
> > > to go upstream it needs changes that breaks the ABI interface to the
> > > firmware which is already shipped and the vendor might not provide
> > > support for updating the firmware file. Having these kind of tightly
> > > coupled interdependencies between driver and firmware is quite risky
> > business.
> > 
> > Yeah, I think we're kind of stuck with some degree of fairly tight coupling at
> > some point though - at some point we're going to need to work out which
> > link in the driver corresponds to which link in the firmware file.
> 
> There is a 'version' field in struct snd_soc_tplg_hdr, which is a vendor-specific version number.
> The driver can check this field of a firmware topology and decide whether to support this firmware or not.
> 
> Is this okay?

Well, you can't assure that the third vendor would set that field
always right.  I won't bet it, as the odds are too bad :)

How about to allow leaving this name empty as default?  Or better to
ask: what's the exact merit of having strict binding to DAI link?


thanks,

Takashi