Messages in this thread | | | Subject | Re: [RFC PATCH 0/3] PM / Domains: Add support for devices that require multiple domains | From | Marek Szyprowski <> | Date | Tue, 29 Nov 2016 12:33:02 +0100 |
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Hi Stephen,
Thanks for pointing to my patches, but I would like to clarify a few things.
On 2016-11-24 03:30, Stephen Boyd wrote: > On 11/22, Jon Hunter wrote: >> On 22/11/16 18:26, Kevin Hilman wrote: >>> Jon Hunter <jonathanh@nvidia.com> writes: >>>> However, I would rather the client of >>>> the power-domains specify which power-domains they require and >>>> dynamically nested the power-domains at runtime. This is slightly >>>> different to what I proposed in this RFC, but it is not really beyond >>>> the bounds of what we support today IMO. What is missing is a means to >>>> do this dynamically and not statically. >>>> >>>> By the way, I am not sure if you are suggesting that for devices that >>>> may need multiple power-domains we should architect the driver >>>> differently and split it up in some way such that we have a power-domain >>>> per device. But for the case of the Tegra XHCI it is quite complex >>>> because the driver loads firmware which runs on a micro-controller and >>>> we need to manage the various power-domains that are used. >>> IMO, constructing a network of new struct devices just to workaround >>> limitations in the framework doesn't sound quite right either. >> I agree. >> > Marek is attempting to do this for the samsung clock > controller[1] (patch #5 is informative).
You probably meant patch #3 / #4, which is a patch for Exynos 4412 ( https://marc.info/?l=linux-arm-kernel&m=147731142926053&w=2 ).
Patch #5 is for Exynos 5433, which already has separate nodes for each clock sub-controller, so there is no problem to add generic power domains there (see multiple CMU nodes):
https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/tree/arch/arm64/boot/dts/exynos/exynos5433.dtsi#n261
> From what I can tell > they have one DT node for their clock controller because it's one > register address space to control clocks. But, certain clocks > exposed by that driver only work when certain power domains are > enabled. For example, they have a clock controller that exposes > clock signals for multimedia hardware blocks like video > accelerators, gpus, and cameras. The clocks seem to have been > placed inside different power domains for the multimedia hardware > they're associated with, so there may be 10 or so power domains > that need to be enabled at different times for different clocks > to work. If the GPU power domain isn't enabled when the GPU > clocks are touched by the driver, things break, etc. > > In the proposed patchset, we have the top-level clock controller > node with subnodes for each power domain that needs to be > associated with clocks inside these different multimedia blocks.
This is valid only for the Exynos4412 case (and not-yet-posted Exynos5422), which has a single clock controller node and patch #4 added a sub-node for ISP clocks part (the only one which in fact is in the other power domain).
> So we end up with one parent device and attached driver for the > clock driver, and then that driver populates child nodes as > devices and matches up clocks with child nodes while registering > clks with clk_register(). Because we pass a dev pointer to > clk_register, we associate different devices with different > clocks all from the same top-level clock controller device > driver. Then clk framework calls runtime_pm APIs with devices > used during clk registration.
Right, this is how I did it for Exynos4412 case.
> Some of those devices don't have > any driver bound to them, which feels odd.
Well, I don't get this. In the proposed patches each sub-node has a separate driver, none is left without a driver.
> This seems like a case where we really want a better way to > explicitly control power domains without making up subnodes and > registering struct devices just to work around the one device to > one genpd construct we have today. Maybe power domains just don't > map to genpd though and that's the disconnect.
Having an API for full control over multiple power domain assigned to a single device node might indeed solve somehow this problem, but as long as runtime pm is tied to struct device, this will again end in creating virtual sub-devices per each power domain to fit runtime pm principles. However we might be able to avoid creating sub-nodes in the device tree.
Best regards -- Marek Szyprowski, PhD Samsung R&D Institute Poland
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