Hi Benoit, Paul,
I've been discussing with Sumit and Archit to understand how the DSS
clocks are set up on OMAP4. I think I now have some idea how things
work, but I'm still at loss why things are the way they are.
So, if I look at OMAP4 TRM, Figure 10-4 DSS Clock Tree, there are two
clocks in PRCM block that are relevant to this discussion: DSS_L3_ICLK
and DSS_FCLK. To my understanding DSS_L3_ICLK is not really
controllable, but it is affected by MODULEMODE bit.
Then we have two relevant clocks defined in clock44xx_data.c: dss_fck
and dss_dss_clk. dss_fck controls the MODULEMODE bit, and dss_dss_clk is
the TRM's DSS_FCLK.
Was that correct?
If so, from DSS driver's perspective, the dss_fck sounds very much like
an interface clock (it's always needed when DSS is used) and dss_dss_clk
sounds very much like functional clock (it's always needed, except if
DSI PLL is used for DSS functional clock).
If "dss_fck" would control DSS_FCLK and "dss_ick" would control
MODULEMODE, they would be about the same as the clocks in OMAP2 and 3,
and we wouldn't need any omap4 spesific trickery in the DSS driver.
("dss_dss_clk" wouldn't be needed).
Why are the clocks set up in this strange fashion?
Tomi
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