Hi Ulf,
On 08/07/2017 02:23 AM, Ulf Hansson wrote:
[...]
I am not sure I get the second part here. The clock to shd is enabled
via a call to clk_prepare_enable(). Unless you explicitly call
clk_disable_unprepare() for it, no? How can any outer logic know when
it can be gated?
This is my understanding. Hope it can make you clear.
The clock tree is like below.
SOC --> [ SDH_CLK_GEN --> SDH_CONTROLLER ] --> SD/EMMC CARD
There is one clock generator inside sdh slot IP, SOC provides the clock to
the sdh slot IP. This clock is enabled/disabled by SW when calling
clk_prepare_enable/clk_disable_unprepare.
The auto clock gating is not any outer logic, it is inside sdh slot IP, when
sdh controller has no activity, the IP will gate the clock from sdh_clk_gen
to sdh_controller. sdh_clk_gen logic itself still has clock from SOC.
With or without runtime pm, the only difference is if sdh_clk_gen has clock
or not. So the power benefit is limited.
Thanks for clarifying!
With SW runtime pm mechanism, compares with HW auto clock gating, the
only
difference is SW cut the source of sdh clock tree, external clock gating
vs
internal clock gating, there will be some benefits, but limited.
Right.
Previously we enabled the runtime pm mechanism in our mobile products,
which
were using the same IP(some old version, including 3 sdh slots) with auto
clock gating feature(the driver is sdhci-pxav3.c). The saving of power
was
about 2~3mA@vcc_main_1.05V(28nm chip) with 3 sdh slots inside soc. No
more
than 1mA/1sdh slot.
1 mA/sdh slot is a great reason to deploy runtime PM support. For a
battery driven device that would be a significant improvement.
Back in the days when I worked at ST-Ericssion, we were chasing uA
when optimizing for power-save. :-)
Definitely for mobile products, but now I didn't see urgent requirement for
our networking products.
I see.
I think what puzzles me is that you do care about saving power in
system sleep, but not during runtime.
I read sdhci-of-at91 driver and your recommended patch, I got your point
is
using a light way for system sleep based on runtime pm feature. From SW
perspective, kill two birds with one stone, it is good.
Right.
But considering about the benefits, it is not that urgent to take runtime
pm
feature as a must, it is a better to have feature. System standby is a
must
feature, without this patch, the system can't work well after resume.
Do you think it is reasonable to add complete standby support at first,
then
take runtime pm as a next step?
You can do that, but why? And will then the "next step" ever happen?
Do you really want to spend efforts in getting something working for
system suspend only, while you instead easily could deploy both
runtime PM and system PM support at the same time?
As Ziji said in another mail, it takes time for next step. The runtime pm
need to be verified completely on all supported boards.
I understand from SW perspective, we'd better have both. But I need input
from internal customers to see if they only request system sleep or they
want both, and what's their priority.
Okay. As I just responded in the other email, I rest my case. :-)
[...]
However, I need an ack from Adrian before I can apply this.
Thanks for your feedback. System level standby is mandatory requirement
from our customer. It's nice you can merge it at first.
For runtime PM, it's nice to have. Actually in the past two weeks I've
already implemented and verified the basic function on our platform.
But it took time for them for the full verification, I will submit
runtime pm patch after hear feedback from them.
Kind regards
Uffe
--
To unsubscribe from this list: send the line "unsubscribe linux-mmc" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
