[linux-sunxi] GSoC 2014 #1 status report - Improving Allwinner SoC support

[Chen-Yu Tsai]

Hi Emilio,

On Sun, Jul 20, 2014 at 3:41 AM, Emilio López <emilio at elopez.com.ar> wrote:
> Hi everyone,
>
> Here's this week's update on my GSoC project; if you missed the first issue
> or you want a refresher of what this is about, you can read it on the list
> archives[0]
>
> A couple of days after the last report, and with the help of Jon Smirl, I
> got the hardware working on mainline Linux, first on only 16 bit stereo
> mode, then mono as well, and later on, also on 24 bit mode. The first thing
> I had to do was rework the cyclic DMA code to make it perform decently and
> avoid underruns. The rest took a bit of playing with values and reading the
> Allwinner documentation. There is one unresolved issue with 24 bit audio
> still - for some reason, the volume is really low compared to the same track
> played on 16 bit. Unfortunately the SDK driver doesn't support 24 bit, so
> it's hard to compare with anything else.

So I have not experimented on this, it's just a hunch:
Could it be that the 24bit audio samples you're sending to the audio codec
is aligned incorrectly? So the sample is actually seen as down-shifted by
8 bits, resulting in the low volume?

I'll grab your tree and test 24bit tomorrow. (Good thing I have 24 bit
music files.) :)

> Aside from the audio stuff, I worked a bit on the DMA driver, after
> realizing memcpy could be optimized a fair bit. By using proper alignment
> and choosing the best bus width and as big a burst as possible, I was able
> to go from a totally unscientifically measured ~3MB/s to ~13MB/s on a single
> thread, single channel, 1000 iterations dmatest run with noverify=0. I will
> be sending a v3 with these new changes as well as addressing comments I
> received in the next few days.

This still seems quite slow? I think there was a discussion about this
on IRC, you included? Any followups there?

> To round up on this week's developments, I also worked on the audio clock
> representation, involving PLL2, the codec clock gate and "module 1" clocks
> (AC97, SPDIF, IIS) to enable Jon to work on IIS. Patches for these clocks
> will be out in the list soon as well.

Thanks! I look forward to them.


Cheers
ChenYu

> You can expect the next status report in about a week's time.
>
> Cheers!
>
> Emilio
>
> [0]
> http://lists.infradead.org/pipermail/linux-arm-kernel/2014-July/271150.html