On Wed, Jul 1, 2015 at 2:49 PM, Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> wrote:
>
> On Tue, Jun 30, 2015 at 05:07:09PM +0800, James Liao wrote:
> > Hi Heiko,
> >
> > There are 4 clocks which are derived from clk_null directly in current
> > topckgen implementation:
> >
> > clkph_mck_o, dpi_ck, usb_syspll_125m, hdmitx_dig_cts
> >
> > Our designer mentioned 2 things about external clocks:
> >
> > 1. These 4 clocks come from analog macro, not from PLL, nor from
> > external clocks directly.
>
> Ok, this means there actually are clocks. We can't control these clock and
> they have some known or unknown rate. This makes them fixed clocks. Just
> specify them in the device tree and you are done. Give them reasonable
> names and the rate if you know it, 0 otherwise.
>
> The problem is not that you use fixed clocks for non software
> controllable clocks of unknwown rates, but that you try to use a single
> clock for all of them and name it 'dummy' or 'null'. Name it
>
> dpi_ck {
> compatible = "fixed-clock";
> rate = <0>; /* unknown, generated by some Analog block */
> };
It would be nice, though, to use the real clock rates.
Otherwise, we end up with a bunch of unknown clock rates, like this:
clock enable_cnt prepare_cnt rate
accuracy phase
----------------------------------------------------------------------------------------
clk_null 2 2 0
0 0
mm_lvds_cts 0 0 0
0 0
mm_lvds_pixel 0 0 0
0 0
mm_dpi1_pixel 0 0 0
0 0
mm_dsi1_digital 0 0 0
0 0
mm_dsi0_digital 1 1 0
0 0
infra_cpum 0 0 0
0 0
hdmitx_dig_cts 0 0 0
0 0
hdmi_sel 0 0 0
0 0
mm_hdmi_pllck 0 0 0
0 0
hdmitxpll_d3 0 0 0
0 0
hdmitxpll_d2 0 0 0
0 0
usb_syspll_125m 0 0 0
0 0
dpi_ck 0 0 0
0 0
clkph_mck_o 1 1 0
0 0
dmpll_d16 0 0 0
0 0
dmpll_d8 0 0 0
0 0
dmpll_d4 0 0 0
0 0
dmpll_d2 0 0 0
0 0
dmpll_ck 1 1 0
0 0
mem_sel 2 2 0
0 0
infra_m4u 1 1 0
0 0
Furthermore, at least some of these children clocks are possible
source clocks for other clocks for which we do want to know the
resulting frequency. For example, the "dmpll_*" clocks are mux inputs
for many of the subsystem clocks.
-Dan
>
> Technically it's the same, but it sounds much more professional and like
> you know what you are doing ;)
>
> Sascha
>
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