Re: [PATCH 1/2] clk: rockchip: dmc: support rk3399 dmc clock driver

From: hl
Date: Mon Nov 23 2015 - 04:20:34 EST

Hi Heiko,

On 22/11/15 02:30, Heiko Stuebner wrote:
Hi Lin,

Am Freitag, 20. November 2015, 09:37:15 schrieb hl:
On 20/11/15 05:47, Heiko Stuebner wrote:
Hi Lin,

Am Donnerstag, 19. November 2015, 18:21:10 schrieb Lin Huang:
support rk3399 dmc clock driver. Note, ddr set rate function will
use dcf controller which run in ATF, it need to fishish it when rk3399
arm trust firmware ready.
this unfinalized state is slightly unfortunate and I think this code will
need to wait until CRU and DDRC specs are available.

Because this is clearly part of the CRU (labeled CRU_CLKSEL6_CON etc)
so shouldn't be a separate driver at all and also what your driver currently
only does can still simply be described in the regular scheme as part of
a full clock driver like

PNAME(mux_ddrc_p) = { "pll_dpll", "pll_gpll", "pll_alpll", "pll_abpll" };
COMPOSITE_NOGATE(0, "ddrc", mux_ddrc_p, 0,
RK3399_CLKSEL_CON(6), 4, 2, MFLAGS, 0, 3,

So the code needs to actually demonstrate why a separate clock type is
really necessary.

I do understand that we will probably need a special way to talk to this
dcf controller but seeing how this interaction will work is really a
prequisite to finding a correct solution.
if we can use common clock driver, i can put the dfi controller as
a independent driver
into devfreq, this is the best way. But how do we separate the ddr
clk_set_rate() ,
so we can manipulate dcf controller(actually, we use SMC handle dcf
controller in arm trust firmware ),
i check clock driver code, it seem there is not way to do that for now.
the core problem I have right now is, that I don't understand how the
interaction with the dfi controller works at all :-) .

One thing that might work, is that your dfi-driver takes the ddrc-clock
from the clock controller and then registers a clock notifier to get
notified before and after the clock-rate changes. But that depends as
stated above on how the dfi-controller needs to be handled.

For example the current armclk-handling uses a clock notifier around the
actual rate change ... so you could use that as inspiration.
Thank you for your inspiration. I think i can handle ddrc clk like the armclk.
About the dfi, it will monitor ddr utilization, according this result to do
ddr frequency scaling. I think i can implement a dfi drvier, and register it to devfreq,
then call the dmc_set_rate fucntion in the dfi drvier, meanwhile i will implement a ddrc clk driver
like the armclk, implement set rate funciton, and call the dcf(implement in ATF) in this function.


Lin Huang

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