[alsa-devel] Using HDA on an SoC without PCI

[Dylan Reid]

On Fri, Feb 14, 2014 at 10:01 AM, Stephen Warren <swarren at wwwdotorg.org> wrote:
> On 02/14/2014 10:47 AM, Dylan Reid wrote:
>> Hi,
>>
>> I'm working on an system with an HDMI codec on an HDA interface, but
>> that interface doesn't use PCI.  I want to re-use as much of the code
>> as possible, but I want to avoid scattering ifdefs all over
>> hda_intel.c.
>
> I think the relevant APIs stub themselves out when appropriate, so you
> can do this all without compile-time ifdefs.
>
>> Would gathering the pci specific functions from hda_intel.c into an
>> interface struct of some kind make sense?  If azx was probed from pci,
>> then a pci interface would be used, if it was a platform driver, then
>> the correct interface for the platform would be used.  It would add
>> some overhead to operations such as azx_writel, but that would be
>> measured to make sure it isn't detrimental to performance.
>
> Our downstream trees do have patches to allow the HDA driver to be
> instantiated from either PCI or from platform devices. You can find the
> code in branch:
>
> git://nv-tegra.nvidia.com/linux-2.6.git rel-roth-r3
> e.g. ef8491346266 "ALSA: hda: Add hda platform driver support"
>
> There are many other patches to sound/pci/hda after that. I don't recall
> exactly how clean taht first patch was, and probably never saw anything
> after it, but it might be a good start...
>
> We've only recently had HDMI support upstream on Tegra, otherwise it's
> possible I may have found time to try to upstream those patches before.
> Not that I have spare time:-)

That is a good start, even better that it's also in 3.10 Tegra kernel.
 That first patch looks pretty good. The following changes to enable
tegra hdmi are a little more interesting, but don't look impossible to
clean up.  The register access is tricky, since the azx_write* defines
need to be different.  I'll play with it for a while and see how it
goes.

Thanks Stephen,

Dylan