Kevin, On Tue, Aug 25, 2015 at 2:07 PM, Kevin Hilman <khilman@xxxxxxxxxx> wrote: > Caesar Wang <wxt@xxxxxxxxxxxxxx> writes: > >> We can add more domains node in the future. >> This patch add the needed clocks into power-controller. >> As the discuess about all the device clocks being listed in >> the power-domains itself. >> >> There are several reasons as follows: >> >> Firstly, the clocks need be turned off to save power when >> the system enter the suspend state. So we need to enumerate >> the clocks in the dts. In order to power domain can turn on and off. > > Yes, but this is the job of device drivers which are runtime PM adapted > to gate their own clocks. I agree these clocks need to be enumerated in > the DTS, but they should be in the device nodes. I _think_ what Caesar means is that the alternative to this patch is to leave the clocks on all the time as they were during the early days of Rockchip (AKA last year). If the clocks are on all the time then the power domain patches can work fine. However, once you start letting clocks turn off then you need to make sure that the power domain code turns the back on temporarily. >> Secondly, the reset-circuit should reset be synchronous on RK3288, >> then sync revoked. So we need to enable clocks of all devices. >> In other words, we have to enable the clocks before you operate them >> if all the device clocks are included in someone domians. > > Yes, this is pretty common for reset. > >> Someone wish was to get the clocks by reading the clocks from the >> device nodes, We can do that but we can solve the above issues. > > I don't follow this sentence. Are you saying doing that will not solve > the above issues? Why not? Please explain. > > If there are non-device clocks that also need to be enabled before > asserting reset, then those are candidates for the power-domain node, > but not device clocks. It's been a long time and I don't know that I've reviewed every revision of this series, but I think there was a proposal that we shouldn't list clocks here. Instead we should search through and find all devices that refer to this power domain, reach in and find their clocks, and turn them on. Did I get that right? To put things in a concrete way, for pd_vio we'd go through the entire device tree ourselves and find all properties that look like "power-domains = <&power RK3288_PD_VIO>;". We'd then find the parent of those properties and look for a property named "clocks". We'd then iterate over all those clocks and turn those on. Did I get that right? The above doesn't seem like a terribly great idea to me for a number of reasons, including: 1. If I remember correctly, it's important to turn on clocks for devices even if they're not something you're using / have a driver for. If you don't then the device won't get reset properly and this can affect things like suspend/resume because the hardware in the SoC will query all devices at suspend time to make sure they're ready. If a device is wedged because its clock wasn't on at the right them then it will cause problems. 2. If we absolutely need to turn all clocks and we get clocks from device tree nodes on then it means we need device tree nodes for every device in the domain. These would be needed even if there are no accepted bindings for this device yet. So we'd need to do one of: A) Block power domain patches on feature complete bindings for all drivers; B) Make up non-approved compatible strings for all devices and throw them into the DTS; C) Add nodes in the DTS without a compatible string just to satisfy the power domain requirements. None of these seem terribly appealing. 3. It is entirely possible that there are clocks that will be listed in the individual devices that aren't needed for powering on the power domain. I'd tend to believe that PCLK_EDP_CTRL (the pixel clock) doesn't really need to be turned on when adjusting the "VIO" power domain. Right now Caesar has it listed, but it probably isn't needed (Caesar: can you confirm?). 4. It seems just slightly brittle to be reaching into other device nodes and making assumptions about their properties. Yeah, it's probably safe to assume that "clocks" has a list of clocks and "power-domains" will point to something whose first entry is a phandle, but it still seems just a tad bit like violating an abstraction barrier. Anyway, perhaps I'm misunderstanding, or perhaps my concerns are simply not for important things. If so feel free to yell at me. ;) >> Anyway, the best ideas we can fix it in the future SoCs. > > I don't think this is an SoC design issue as this is needed when you > have synchronous reset. My concern is primarily around how to describe > this in the DT. I suppose the SoC could override things and make sure clocks are on in this case? ...or if a clock is off it could defer powering it up somehow until the clock came on? ...dunno how this actually looks in hardware. In any case letting devices get wedged doesn't seem ideal... -Doug -- 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
