On Thu, 5 Sep 2024 20:26:15 +0800 Chen-Yu Tsai <wens@xxxxxxxx> wrote: > Hi, > > On Thu, Sep 5, 2024 at 8:17 PM Dragan Simic <dsimic@xxxxxxxxxxx> wrote: > > > > Hello, > > > > Just checking, any further thoughts about this patch? > > Sorry, but I feel like it's not really worth the churn. There's not > really a problem to be solved here. What you are arguing for is more > about aesthetics, and we could argue that having them separate makes > it easier to read and turn on/off. Yeah, I agree. If a board wants to support OPPs, they just have to include a single file and define the CPU regulator, and that's a nice opt-in, IMHO. But having this patch would make it quite hard to opt out, I believe. For Linux there are probably ways to disable DVFS nevertheless, but I am not sure this is true in an OS agnostic pure-DT-only way. This could probably be solved, but same as Chen-Yu I don't see any good enough reason for this patch in the first place. Cheers, Andre > And even though the GPU OPPs are in the dtsi, it's just one OPP acting > as a default clock rate. > > > ChenYu > > > On 2024-08-17 06:25, Dragan Simic wrote: > > > Hello Andre, > > > > > > On 2024-08-15 19:15, Andre Przywara wrote: > > >> On Thu, 15 Aug 2024 18:34:58 +0200 > > >> Dragan Simic <dsimic@xxxxxxxxxxx> wrote: > > >>> On 2024-08-14 18:11, Chen-Yu Tsai wrote: > > >>> > On Wed, Aug 14, 2024 at 1:52 PM Dragan Simic <dsimic@xxxxxxxxxxx> > > >>> > wrote: > > >>> >> > > >>> >> Move the Allwinner A64 CPU OPPs to the A64 SoC dtsi file and, > > >>> >> consequently, > > >>> >> adjust the contents of the affected board dts(i) files appropriately, > > >>> >> to > > >>> >> "encapsulate" the CPU OPPs into the SoC dtsi file. > > >>> >> > > >>> >> Moving the CPU OPPs to the SoC dtsi file, instead of requiring the > > >>> >> board > > >>> >> dts(i) files to include both the SoC dtsi file and the CPU OPP dtsi > > >>> >> file, > > >>> >> reduces the possibility for incomplete SoC data inclusion and improves > > >>> >> the > > >>> >> overall hierarchical representation of data. Moreover, the CPU OPPs > > >>> >> are > > >>> >> not used anywhere but together with the SoC dtsi file, which > > >>> >> additionally > > >>> >> justifies the folding of the CPU OPPs into the SoC dtsi file. > > >>> >> > > >>> >> No functional changes are introduced, which was validated by > > >>> >> decompiling and > > >>> >> comparing all affected board dtb files before and after these changes. > > >>> >> When > > >>> >> compared with the decompiled original dtb files, the updated dtb files > > >>> >> have > > >>> >> some of their blocks shuffled around a bit and some of their phandles > > >>> >> have > > >>> >> different values, as a result of the changes to the order in which the > > >>> >> building blocks from the parent dtsi files are included into them, but > > >>> >> they > > >>> >> still effectively remain the same as the originals. > > >>> > > > >>> > IIRC, this was a conscious decision requiring board dts files to set > > >>> > their > > >>> > CPU supply before OPPs are given. The bootloader does not boot the SoC > > >>> > at the highest possible OPP / regulator voltage, so if the OPPs are > > >>> > given > > >>> > but the supply is not, the kernel will attempt to raise the frequency > > >>> > beyond what the current voltage can supply, causing it to hang. > > >> > > >> Yes, this is what I remember as well: this forces boards to opt in to > > >> DVFS, otherwise they get a fixed 816 MHz. Since there is only one OPP > > >> table for all boards with that SoC, I think it's reasonable to ask for > > >> this, since the cooling could not be adequate for higher frequencies > > >> in > > >> the first place, or the power supply is not up to par. > > > > > > If the cooling isn't capable enough to dissipate the additional heat > > > generated at higher frequencies, the thermal governor is there to > > > handle > > > that by lowering the operating frequency. If the PSU isn't capable to > > > provide an additional watt or two, I think a better PSU is needed. :) > > > No reasonably sized PSU should work at ~100% of its power output. > > > > > > On top of that, all currently supported A64-based boards have the CPU > > > OPPs defined and CPU DVFS enabled, so no such issues are possible > > > there. > > > Though, there could be some issues with new A64-based boards, which is > > > discussed further below. > > > > > >>> > Now that all existing boards have it properly enabled, there should be > > >>> > no > > >>> > need for this. However I would appreciate a second opinion. > > >> > > >> Well, since there is no way to opt *out* now, I am somewhat reluctant > > >> to > > >> just have this. What is the actual problem we are solving here? After > > >> all > > >> there is just one OPP table for all A64 boards, so there is less > > >> confusion > > >> about what to include in each board file. Which IIUC is a more > > >> complicated > > >> situation on the Rockchip side. > > > > > > Well, this patch doesn't solve some real problem, but it makes the > > > things > > > neater and a bit more clean. The things are more complicated with > > > Rockchip > > > SoCs, but following the concept of "encapsulating" the CPU OPPs into > > > the > > > A64 SoC dtsi makes things neater. Moreover, the A64 GPU OPPs are > > > already > > > in the A64 SoC dtsi, so we could also say that folding the A64 CPU OPPs > > > into the SoC dtsi follows the A64 GPU OPPs. > > > > > >> I still have to try "operating-points-v2", but at least on the H616 > > >> side > > >> putting a 'status = "disabled";' into the OPP node didn't prevent it > > >> from > > >> probing. Otherwise this would have been a nice compromise, I think. > > >> > > >>> Good point, thanks for the clarification. This is quite similar to > > >>> how > > >>> board dts(i) files for Rockchip SoCs need to enable the SoC's > > >>> built-in > > >>> TSADC for temperature sensing, before the CPU thermal throttling can > > >>> actually work and prevent the SoC from overheating, etc. > > >>> > > >>> The consensus for Rockchip boards is that it's up to the authors and > > >>> reviewers of the board dts(i) files to make sure that the built-in > > >>> TSADC > > >>> is enabled, etc. With that approach in mind, and knowing that all > > >>> Allwinner > > >>> A64 board dts(i) files are in good shape when it comes to the > > >>> associated > > >>> voltage regulators, I think it's fine to follow the same approach of > > >>> "encapsulating" the CPU OPPs into the A64 SoC dtsi file. > > >> > > >> As mentioned above, I am not so sure about this. With this patch here, > > >> *every* board gets DVFS. And while this seems to be fine when looking > > >> at > > >> the current DTs in the tree (which have it anyway), it creates a > > >> potentially dangerous situation for new boards. > > >> > > >> So pragmatically speaking, this patch would be fine, but it leaves me > > >> a > > >> bit uneasy about future or downstream boards. > > > > > > Frankly, I wouldn't be worried about that. When a new A64-based board > > > is added, it should be verified that CPU DVFS works as expected, etc., > > > before the new board dts file is accepted upstream. > > > > > > Maybe we could take into account some possible issues when someone > > > starts > > > putting together a new A64-based board dts file, but there are already > > > many dangerous things that someone can do in the process, such as > > > messing > > > up various regulators and voltages unrelated to the CPU DVFS, so > > > everyone > > > putting a new board dts file together simply have to know what are they > > > doing. I see no way for escaping from that need. > > > > > [...]
