Hi, On Thu, Sep 8, 2022 at 7:29 AM Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx> wrote: > > On 08/09/2022 16:23, Doug Anderson wrote: > > Hi, > > > > On Thu, Sep 8, 2022 at 3:25 AM Krzysztof Kozlowski > > <krzysztof.kozlowski@xxxxxxxxxx> wrote: > >> > >> On 07/09/2022 22:49, Andrew Halaney wrote: > >>> For RPMH regulators it doesn't make sense to indicate > >>> regulator-allow-set-load without saying what modes you can switch to, > >>> so be sure to indicate a dependency on regulator-allowed-modes. > >>> > >>> In general this is true for any regulators that are setting modes > >>> instead of setting a load directly, for example RPMH regulators. A > >>> counter example would be RPM based regulators, which set a load > >>> change directly instead of a mode change. In the RPM case > >>> regulator-allow-set-load alone is sufficient to describe the regulator > >>> (the regulator can change its output current, here's the new load), > >>> but in the RPMH case what valid operating modes exist must also be > >>> stated to properly describe the regulator (the new load is this, what > >>> is the optimum mode for this regulator with that load, let's change to > >>> that mode now). > >>> > >>> With this in place devicetree validation can catch issues like this: > >>> > >>> /mnt/extrassd/git/linux-next/arch/arm64/boot/dts/qcom/sm8350-hdk.dtb: pm8350-rpmh-regulators: ldo5: 'regulator-allowed-modes' is a dependency of 'regulator-allow-set-load' > >>> From schema: /mnt/extrassd/git/linux-next/Documentation/devicetree/bindings/regulator/qcom,rpmh-regulator.yaml > >>> > >>> Where the RPMH regulator hardware is described as being settable, but > >>> there are no modes described to set it to! > >>> > >>> Suggested-by: Johan Hovold <johan+kernel@xxxxxxxxxx> > >>> Reviewed-by: Johan Hovold <johan+kernel@xxxxxxxxxx> > >>> Reviewed-by: Douglas Anderson <dianders@xxxxxxxxxxxx> > >>> Signed-off-by: Andrew Halaney <ahalaney@xxxxxxxxxx> > >>> --- > >>> > >>> v2: https://lore.kernel.org/linux-arm-msm/20220906201959.69920-1-ahalaney@xxxxxxxxxx/ > >>> Changes since v2: > >>> - Updated commit message to explain how this is a property of the > >>> hardware, and why it only applies to certain regulators like RPMH > >>> (Johan + Krzysztof recommendation) > >>> - Added Johan + Douglas' R-B tags > >> > >> You posted before we finished discussion so let me paste it here: > >> > >> The bindings don't express it, but the regulator core explicitly asks > >> for set_mode with set_load callbacks in drms_uA_update(), which depends > >> on REGULATOR_CHANGE_DRMS (toggled with regulator-allow-set-load). > >> > >> drms_uA_update() later calls regulator_mode_constrain() which checks if > >> mode changing is allowed (REGULATOR_CHANGE_MODE). > >> > >> Therefore based on current implementation and meaning of > >> set-load/allowed-modes properties, I would say that this applies to all > >> regulators. I don't think that RPMh is special here. > > > > RPMh is special compared to RPM because in RPMh the hardware exposes > > "modes" to the OS and in RPM the hardware doesn't. Specifically: > > > > In RPM, the OS (Linux) has no idea what mode the regulator is running > > at and what modes are valid. The OS just tells the RPM hardware "I'm > > requesting a load of X uA. Thanks!" So "regulator-allow-set-mode" > > basically says "yeah, let the OS talk to RPM about loads for this > > regulator. > > So how does set load works for this case? You mentioned > "allow-set-mode", but we talk about "allow-set-load". Ah, sorry. I meant "allow-set-load". > > In RPMh, the OS knows all about the modes. For each regulator it's the > > OS's job to know how much load the regulator can handle before it > > needs to change modes. So the OS adds up all the load requests from > > all the users of the regulator and then translates that to a mode. The > > OS knows all about the modes possible for the regulator and limiting > > them to a subset is a concept that is sensible. > > > > This is why, for instance, there can be an "initial mode" specified > > for RPMh but not for RPM. The OS doesn't ever know what mode a RPM > > regulator is in but it does for RPMh. > > Sorry, I don't find it related. Whether RPM has modes or not, does not > matter to this discussion unless it sets as well allow-set-load without > the mode... and then how does it work? In current implementation it > shouldn't... >From looking at the source code of Linux: * allow-set-load basically says whether the core regulator framework even pays attention when drivers specify how much load they're using. * On RPM then if allow-set-load is set then we'll sum up all of the load requests from clients and pass it to hardware. * On RPMH, if allow-set-load is set then we'll sum up all the load requests, translate that to a mode, validate it against the set of "allowable" modes, and if it's valid then pass it to hardware. -Doug
