Re: [PATCH 1/4] soc/sound: tegra_max98090: do not invert headphone jack

[Jonathan Tinkham <sctincman-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 02/04/2016 09:36 AM, Stephen Warren wrote:
> On 02/03/2016 10:30 PM, Jonathan Tinkham wrote:
>> The headphone jack should not be inverted
>
> Have you tested this on Venice2 as well as Nyan? I'm pretty sure 
> Venice2 was tested when this driver was written, and whoever added 
> Nyan support to the kernel simply assumed it would work. As such, my 
> suspicion is that this series will break Venice2 even as it fixes Nyan.

I have not tested this on Venice2, only on Nyan. That seems like a 
plausible cause and reasonable suspicion.

> Why doesn't user-space expect what the kernel actually implements? The 
> kernel should be defining the control naming.
>
> Which user-space are you using specifically, and which part of it 
> expects particular naming?
>
> Perhaps this series needs to be parametrized based on a flag in DT, 
> rather than switching the hard-coded values, so that only Venice2 can 
> be affected?

Specifically pulse-audio and alsa under Arch Linux.

I was referencing 'Documentation/sound/alsa/soc/dapm.txt' with regards 
to control names. While it is possible to add another entry into the 
user-space configuration, I took this documentation as a definition of 
kernel control naming schemes, and thought the driver had used a 
non-standard naming scheme (or at least, not a consistent one).

> On 02/03/2016 10:31 PM, Jonathan Tinkham wrote:
>> Update device-tree bindings to reflect the rename of the board's
>> headphone jack.
>
> This looks like an incompatible change to the DT. While you've fixed 
> the DT, which will fix new installations, old DTs now won't work. This 
> breaks DT ABI. Any DT change needs to be backwards compatible, i.e. 
> the old name should still work and be documented as a legacy value. 

I see that now. If the inversion behavior differs between venice2 and 
nyan, then another compatible string would need to be added anyways, 
correct? As you mentioned above, this might need to be done anyways for 
the rename.

Something like:
- "compatible = nvidia,tegra-audio-max98090" implements old inversion 
behavior and leaves the switch as "Headphones" to avoid breaking older DTs
- "compatible = nvidia,tegra-{venice2,nyan}-audio-max98090" that 
separates the inversion behavior and also introduces the rename