On 09/12/15 12:23, Jon Hunter wrote: > > On 08/12/15 19:07, Kevin Hilman wrote: >> Jon Hunter <jonathanh@xxxxxxxxxx> writes: >> >>> Add power-domain binding documentation for the NVIDIA PMC driver in >>> order to support generic power-domains. >>> >>> Signed-off-by: Jon Hunter <jonathanh@xxxxxxxxxx> >>> >>> --- >>> >>> Please note that I have been debating whether I add this >>> "nvidia,powergate-clock-disable" property or just leave the clocks >>> disabled by default. Some downstream kernels leave the clocks enabled >>> for the audio power-domain because the clocks required for powering up >>> the power-domain are needed by all modules within the power-domain. >>> However are the same time there are other power-domains that may need >>> to be on, but not always clocked and so having the ability to specify if >>> the clocks should be disabled seems useful. However, I can also remove >>> this and just have the appropriate devices turn on the clocks as well. >>> --- >>> .../bindings/arm/tegra/nvidia,tegra20-pmc.txt | 61 ++++++++++++++++++++++ >>> 1 file changed, 61 insertions(+) >>> >>> diff --git a/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-pmc.txt b/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-pmc.txt >>> index 838e1a69ec0a..8e4641db51a9 100644 >>> --- a/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-pmc.txt >>> +++ b/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-pmc.txt >>> @@ -1,5 +1,7 @@ >>> NVIDIA Tegra Power Management Controller (PMC) >>> >>> +== Power Management Controller Node == >>> + >>> The PMC block interacts with an external Power Management Unit. The PMC >>> mostly controls the entry and exit of the system from different sleep >>> modes. It provides power-gating controllers for SoC and CPU power-islands. >>> @@ -69,6 +71,10 @@ Optional properties for hardware-triggered thermal reset (inside 'i2c-thermtrip' >>> Defaults to 0. Valid values are described in section 12.5.2 >>> "Pinmux Support" of the Tegra4 Technical Reference Manual. >>> >>> +Optional nodes: >>> +- pm-domains : This node contains a hierarchy of PM domain nodes, which should >>> + match the power-domains on the Tegra SoC. >>> + >>> Example: >>> >>> / SoC dts including file >>> @@ -114,3 +120,58 @@ pmc@7000f400 { >>> }; >>> ... >>> }; >>> + >>> + >>> +== PM Domain Nodes == >>> + >>> +Each of the PM domain nodes represents a power-domain on the Tegra SoC >>> +that can be power-gated by the PMC and should be named appropriately. >>> + >>> +Required properties: >>> + - clocks: Must contain an entry for each clock required by the PMC for >>> + controlling a power-gate. See ../clocks/clock-bindings.txt for details. >> >> We've had this discussiona for a couple of other SoCs, so I need to >> ask... >> >> Presumably these are not device clocks that a runtime PM enabled driver >> should be managing for a device, right? IOW, We want to make sure that the >> PM domain isn't managing clocks for drivers that should be doing it. >> >> I understand there are legitimate reasons for the PM domain to manage >> clocks in addition to device drivers (e.g. for synchronous reset), but >> just want to be sure it's not a shortcut for having a proper driver. > > So some clocks may also be used by devices, but they are needed as part > of the power ungating/gating sequence. The general power-up sequence for > tegra is ... > > 1. Enable the power-domain > 2. Enable the clock(s) > 3. Remove signal clamps > 4. De-assert reset(s) > 5. Disable clocks (optional) > > You may say we should only handle #1 above for the powering up sequence, > but we can't do this. The reason is that there is one bit for each > power-domain that controls the signaling clamps and so we need to turn > on all the clocks specified in the TRM before we do this. Once we have > done this and released the reset(s), we can then disable the clocks > again (shown above an optional as it is not mandatory from a design > perspective) and then the devices in the power-domain should enable the > clocks they need as and when they want them. > > Please note that I 100% agree that all clocks required by a device are > handled by the device and we do not implement any short-cuts here. The > only question I had was if there are clocks that may be bus clocks in > the power-domain that are required by all device in the power-domain. > However, may be this should be represented as a bus driver and all the > devices are children of it? Although the "nvidia,powergate-disable-clocks" optional property I had proposed could be seen as a bit of a short-cut, it is true :-) May be I should make the disabling of clocks again mandatory for the power-up sequence. Jon -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html