Hi,
On 2015年10月13日 00:03, Heiko Stübner wrote:
Am Sonntag, 11. Oktober 2015, 12:41:09 schrieb Heiko Stübner:
Hi Stephen,
Am Donnerstag, 8. Oktober 2015, 14:58:40 schrieb Stephen Boyd:
On 10/02, Heiko Stübner wrote:
Hi,
any comment on these 3 patches?
Dong has a similar problem, but those patches conflate this with
enabling parent clocks during clk_disable_unused() which makes no
sense to me. So I'm ok with the requirement that we turn clocks
on to change rates, but I wonder if in this case we need to turn
on the clock that's changing rates itself, or if we just need to
turn on the parent and/or future parent of the clock during the
rate switch. Care to elaborate on that?
As you can see in the follow-up patches, the fractional dividers on Rockchip
SoCs are quite strange in that they even need to have their _downstream_
mux point to them to actually accept rate changes.
The register value always reflects the value set by the system, but hardware
really only accepts it if the clock is enabled and even the downstream mux
selects the fractional divider as parent (they call it a auto-gating
feature).
So in the worst (and current) case, you end up with the register showing the
right value, but the hardware can use completely different dividers from
the previous setting.
That strange behaviour got quite deeply investigated between Rockchip and
Google engineers who stumbled upon this in the first place, so I'm
reasonably sure this is the right solution for that clock type :-) .
Xing Zheng now also independently stumbled upon this issue with his rk3036
work. And came to the same conclusion that the gate must be enabled as well as
the downstream mux be set to the fractional divider for it to actually accept
a new setting.
Yes, I discussed such problems with Heiko about the question:
The RK3036 i2s frac(CRU_SEL7_CON) set value is invalid when I playback a
48KHz music:
/ # io -4 0x20000060
20000060: 01003057
read register is 0x01003057, but the result of frac divider on the basis
of default 0x0bb8ea60(numerator=3000, denominator=60000, ratio=20), so
the out of mclk remains 594/20=29.7MHz
I tracked the logs:
[ 49.770322] clk_fd_set_rate: 91, name: i2s_frac, rate = 12288000,
parent_rate = 594000000
[ 49.778524] clk_fd_set_rate: 107, name: i2s_frac, val = 0x01003057
[ 49.784714] clk_fd_recalc_rate: 29, name: i2s_frac, parent_rate = 594000000
[ 49.791707] clk_fd_recalc_rate: 47, name: i2s_frac, val = 0x01003057, m
= 256, n = 12375
[ 49.799836] clk_mux_set_parent: 81, name: i2s_pre
It seem like set i2s_frac_div then set mux is i2s_pre. I think we should
select the correct mux and open clock gate, then set the i2s_frac_div,
and I tried to do it, setting i2s_frac_div is vaild and mclk is
12.288MHz. Therefore, I think that select parent mux and enable gate
should before child node set value.
Thanks. :)
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