Re: [PATCH 19/27] OMAP: DSS2: Use PM runtime & HWMOD support

On Mon, 2011-06-06 at 15:15 +0200, Cousson, Benoit wrote:

On 6/6/2011 3:01 PM, Valkeinen, Tomi wrote:

quoted

On Mon, 2011-06-06 at 14:56 +0200, Cousson, Benoit wrote:

quoted

In this long term solution, if the dss_fclk is the main_clk, how does
the framework handle the situation when we want to switch from the
standard DSS fclk to the one from DSI PLL?

That part cannot be done by the hwmod fmwk anyway. The goal of the fmwk 
is to ensure that the module is accessible by the driver whatever the 
PRCM clock used.
Enabling the DSI PLL will require the PRCM clock to be enabled first.

Using the DSI PLL as the fclk is doable, but is it really useful or needed?

Yes, it's useful and needed. It gives us much finer control to the clock
frequencies, and so allows us to go to higher frequencies and also more
exactly to the required pixel clock.

Assuming you need that mode, you will always have to explicitly switch 
from DSI to PRCM clock before trying to disable the DSS.
This is something you will have to do inside the DSS driver. It should 
be transparent to the hwmod fmwk.

This sounds ok.

I think the main question is how do we disable the standard DSS fclk
from PRCM when using DSI PLL? As far as I know, disabling that clock
will allow some areas of OMAP to be shut down even while DSS is working.
So from power management point of view it sounds a needed feature.

If the clock is main_clk for the HWMOD, it sounds to me it's always
enabled if the HWMOD is enabled?

 Tomi