Re: [RFC][PATCH 0/7] Add HDMI audio support for HiKey

[John Stultz]

On Fri, Jul 15, 2016 at 8:15 PM, Andy Green <andy@xxxxxxxxxxx> wrote:
> On Fri, 2016-07-15 at 19:13 -0700, John Stultz wrote:
>> This patch set is required for HDMI audio support on HiKey.
>>
>> This patchset hasn't yet seen the light of lkml, so I suspect
>> there will be a few revisions, but I wanted to send it out for
>> an initial review.
>>
>> The work is mostly that of Andy Green's, but I've taking a swing
>> at forward porting and cleaning it up where I saw fit. So credit
>> to Andy and blame to me. Apologies in advance, as I'm not super
>> familiar with either DMA or ASoC driver.
>>
>> The one bit missing to have audio fully working is changes to the
>> adv7511 driver, but most of those changes are still out of tree, so
>> I'll submit those changes once they land.
>>
>> Feedback would be very much appreicated!
>
> Thanks John, it's good to know that work didn't go to waste.
>
> The linaro.org email in the patches is dead, since I resigned from
> Linaro a few months ago.  If the goal of adding it to the kernel is to
> make it possible to contact the author, it should change to
> <andy@xxxxxxxxxxx>.

Yea. I'm not sure what the communities policy on Author/SoB lines in
the face of email address changes.
For the moment I'll leave the credit lines as is (since that's how I
got them, and changing SoB's is usually a big no no). But if others
have advice on how to best handle this I'd appreciate it. I'll be sure
to leave your new email in the Cc: entries.
(Though I need to figure out how to get git send-email to not cc the
author line to avoid the reply-all noise)

> There are (were) a couple of limitations with it that should be
> commented somewhere:
>
>  1) The cyclic DMA, at least going into the I2S FIFO, had what appeared
> to be hw bugs when I left it, I had asked hisilicon about it but got no
> useful reply.  The DMA worked well generally, but there were audible
> clicks and pops at intervals even though the DMA really is cyclic.  I
> dunno whether they got around to looking at it or not: if not, there
> should probably be a comment in the driver about it.  There were notes
> in the I2S FIFO docs (it seemed the likely culprit) about needing to
> take care about FIFO trigger levels but didn't seem to change anything.

So against the 4.4 and later kernels, I've no longer had trouble with
the pops and noise. There is an outstanding issue of a occasional DMA
error from the hardware on the first transfer after opening the audio
device, but some of the HiSi folks are looking into that.

>  2) The driver only exposes 48kHz / 2ch.

Yea. I've limited the i2s/hdmi-card driver to only 48k to match.

thanks
-john