On Wed, 14 Feb 2024 at 05:29, Jagadeesh Kona <quic_jkona@xxxxxxxxxxx> wrote: > > > > On 2/13/2024 7:21 PM, Ulf Hansson wrote: > > On Tue, 13 Feb 2024 at 14:10, Jagadeesh Kona <quic_jkona@xxxxxxxxxxx> wrote: > >> > >> > >> > >> On 2/2/2024 5:59 PM, Ulf Hansson wrote: > >>> On Fri, 2 Feb 2024 at 00:51, Bjorn Andersson <andersson@xxxxxxxxxx> wrote: > >>>> > >>>> On Wed, Jan 31, 2024 at 01:12:00PM +0100, Ulf Hansson wrote: > >>>>> On Wed, 31 Jan 2024 at 02:09, Bjorn Andersson <andersson@xxxxxxxxxx> wrote: > >>>>>> > >>>>>> On Mon, Jan 22, 2024 at 10:47:01AM +0200, Abel Vesa wrote: > >>>>>>> From: Ulf Hansson <ulf.hansson@xxxxxxxxxx> > >>>>>>> > >>>>>>> Some power-domains may be capable of relying on the HW to control the power > >>>>>>> for a device that's hooked up to it. Typically, for these kinds of > >>>>>>> configurations the consumer driver should be able to change the behavior of > >>>>>>> power domain at runtime, control the power domain in SW mode for certain > >>>>>>> configurations and handover the control to HW mode for other usecases. > >>>>>>> > >>>>>>> To allow a consumer driver to change the behaviour of the PM domain for its > >>>>>>> device, let's provide a new function, dev_pm_genpd_set_hwmode(). Moreover, > >>>>>>> let's add a corresponding optional genpd callback, ->set_hwmode_dev(), > >>>>>>> which the genpd provider should implement if it can support switching > >>>>>>> between HW controlled mode and SW controlled mode. Similarly, add the > >>>>>>> dev_pm_genpd_get_hwmode() to allow consumers to read the current mode and > >>>>>>> its corresponding optional genpd callback, ->get_hwmode_dev(), which the > >>>>>>> genpd provider can also implement for reading back the mode from the > >>>>>>> hardware. > >>>>>>> > >>>>>>> Signed-off-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx> > >>>>>>> Signed-off-by: Abel Vesa <abel.vesa@xxxxxxxxxx> > >>>>>>> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx> > >>>>>>> --- > >>>>>>> drivers/pmdomain/core.c | 69 +++++++++++++++++++++++++++++++++++++++++++++++ > >>>>>>> include/linux/pm_domain.h | 17 ++++++++++++ > >>>>>>> 2 files changed, 86 insertions(+) > >>>>>>> > >>>>>>> diff --git a/drivers/pmdomain/core.c b/drivers/pmdomain/core.c > >>>>>>> index a1f6cba3ae6c..41b6411d0ef5 100644 > >>>>>>> --- a/drivers/pmdomain/core.c > >>>>>>> +++ b/drivers/pmdomain/core.c > >>>>>>> @@ -548,6 +548,75 @@ void dev_pm_genpd_synced_poweroff(struct device *dev) > >>>>>>> } > >>>>>>> EXPORT_SYMBOL_GPL(dev_pm_genpd_synced_poweroff); > >>>>>>> > >>>>>>> +/** > >>>>>>> + * dev_pm_genpd_set_hwmode - Set the HW mode for the device and its PM domain. > >>>>>> > >>>>>> This isn't proper kernel-doc > >>>>> > >>>>> Sorry, I didn't quite get that. What is wrong? > >>>>> > >>>> > >>>> https://docs.kernel.org/doc-guide/kernel-doc.html#function-documentation > >>>> says that there should be () after the function name, and below there > >>>> should be a Return: > >>> > >>> Thanks for the pointers! > >>> > >>>> > >>>>>> > >>>>>>> + * > >>>>>>> + * @dev: Device for which the HW-mode should be changed. > >>>>>>> + * @enable: Value to set or unset the HW-mode. > >>>>>>> + * > >>>>>>> + * Some PM domains can rely on HW signals to control the power for a device. To > >>>>>>> + * allow a consumer driver to switch the behaviour for its device in runtime, > >>>>>>> + * which may be beneficial from a latency or energy point of view, this function > >>>>>>> + * may be called. > >>>>>>> + * > >>>>>>> + * It is assumed that the users guarantee that the genpd wouldn't be detached > >>>>>>> + * while this routine is getting called. > >>>>>>> + * > >>>>>>> + * Returns 0 on success and negative error values on failures. > >>>>>>> + */ > >>>>>>> +int dev_pm_genpd_set_hwmode(struct device *dev, bool enable) > >>>>>>> +{ > >>>>>>> + struct generic_pm_domain *genpd; > >>>>>>> + int ret = 0; > >>>>>>> + > >>>>>>> + genpd = dev_to_genpd_safe(dev); > >>>>>>> + if (!genpd) > >>>>>>> + return -ENODEV; > >>>>>>> + > >>>>>>> + if (!genpd->set_hwmode_dev) > >>>>>>> + return -EOPNOTSUPP; > >>>>>>> + > >>>>>>> + genpd_lock(genpd); > >>>>>>> + > >>>>>>> + if (dev_gpd_data(dev)->hw_mode == enable) > >>>>>> > >>>>>> Between this and the gdsc patch, the hw_mode state might not match the > >>>>>> hardware state at boot. > >>>>>> > >>>>>> With hw_mode defaulting to false, your first dev_pm_genpd_set_hwmode(, > >>>>>> false) will not bring control to SW - which might be fatal. > >>>>> > >>>>> Right, good point. > >>>>> > >>>>> I think we have two ways to deal with this: > >>>>> 1) If the provider is supporting ->get_hwmode_dev(), we can let > >>>>> genpd_add_device() invoke it to synchronize the state. > >>>> > >>>> I'd suggest that we skip the optimization for now and just let the > >>>> update hit the driver on each call. > >>> > >>> Okay. > >>> > >>>> > >>>>> 2) If the provider doesn't support ->get_hwmode_dev() we need to call > >>>>> ->set_hwmode_dev() to allow an initial state to be set. > >>>>> > >>>>> The question is then, if we need to allow ->get_hwmode_dev() to be > >>>>> optional, if the ->set_hwmode_dev() is supported - or if we can > >>>>> require it. What's your thoughts around this? > >>>>> > >>>> > >>>> Iiuc this resource can be shared between multiple clients, and we're > >>>> in either case returning the shared state. That would mean a client > >>>> acting upon the returned value, is subject to races. > >>> > >>> Not sure I understand this, but I also don't have in-depth knowledge > >>> of how the HW works. > >>> > >>> Isn't the HW mode set on a per device basis? > >>> > >>>> > >>>> I'm therefore inclined to say that we shouldn't have a getter, other > >>>> than for debugging purposes, in which case reading the HW-state or > >>>> failing would be reasonable outcomes. > >>> > >>> If you only want this for debug purposes, it seems better to keep it > >>> closer to the rpmh code, rather than adding generic callbacks to the > >>> genpd interface. > >>> > >>> So to conclude, you think having a ->set_hwmode_dev() callback should > >>> be sufficient and no caching of the current state? > >>> > >>> Abel, what's your thoughts around this? > >>> > >> > >> We believe it is good to have get_hwmode_dev() callback supported from > >> GenPD, since if multiple devices share a GenPD, and if one device moves > >> the GenPD to HW mode, the other device won't be aware of it and second > >> device's dev_gpd_data(dev)->hw_mode will still be false. > >> > >> If we have this dev_pm_genpd_get_hwmode() API supported and if we assign > >> dev_gpd_data(dev)->hw_mode after getting the mode from get_hwmode_dev() > >> callback, consumer drivers can use this API to sync the actual HW mode > >> of the GenPD. > > > > Hmm, I thought the HW mode was being set on a per device basis, via > > its PM domain. Did I get that wrong? > > > > Are you saying there could be multiple devices sharing the same PM > > domain and thus also sharing the same HW mode? In that case, it sure > > sounds like we have synchronization issues to deal with too. > > > > Sorry my bad, currently we don't have usecase where multiple devices > sharing the same PM domain that have HW control support, so there is no > synchronization issue. Okay, good! > > But it would be good to have .get_hwmode_dev() callback for consumer > drivers to query the actual GenPD mode from HW, whenever they require it. Okay, no objection from my side. Then the final question is if we need a variable to keep a cache of the current HW mode for each device. Perhaps we should start simple and just always invoke the callbacks from genpd, what do you think? Kind regards Uffe
