Re: v3.4-rc4 DSS PM problem (Was: Re: Problems with 3.4-rc5)

[Tomi Valkeinen <tomi.valkeinen@ti.com>]

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On Wed, 2012-05-16 at 12:09 +0200, Cousson, Benoit wrote:
> Hi Tomi,
> 
> On 5/16/2012 11:08 AM, Tomi Valkeinen wrote:

> > Disabling DPLL3 autoidle fixes the problem. Disabling DPLL4 autoidle
> > doesn't affect the problem.
> 
> The issues your are facing seems to be the well known DSS low power 
> refresh mode we've been trying to use since OMAP2 :-).

Hmm, so are you saying no one has managed to get fifomerge and autoidle
working reliably? If so, no point for me to even try it =).

If so, I wonder which is better to have: fifomerge or autoidle... 

> > I also suspect that this could be just a plain DSS bug. The default FIFO
> > low/high thresholds are 960/1023 bytes (i.e. DSS starts refilling the
> > FIFO when there are 960 or less bytes in the fifo, and stops at 1023.
> > The fifo is 1024 bytes). The values are calculated with fifo_size -
> > burst_size and fifo_size - 1.
> >
> > We are now using FIFO merge features, which combines multiple fifos into
> > one when possible, making the fifo size 1024*3 = 3072. Using the same
> > low threshold and increasing the high threshold to 960/3071 works fine.
> > Changing the high threshold to 3008 causes underflows. Increasing the
> > low threshold to ~1600 makes DSS work again.
> 
> That's weird, in theory what should matter is only the diff between the 
> high and low. Well the low value should be as high as possible as well 
> to support the wakeup latency.

Yep. That makes me think there's some kind of problem with DSS accessing
the memory with particular fifo thresholds.

 Tomi


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