From: Pavan Kondeti <quic_pkondeti@quicinc.com>
To: Stephen Boyd <swboyd@chromium.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>,
Felipe Balbi <balbi@kernel.org>,
Matthias Kaehlcke <mka@chromium.org>,
Pavan Kondeti <quic_pkondeti@quicinc.com>,
Krishna Kurapati <quic_kriskura@quicinc.com>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
Rob Herring <robh+dt@kernel.org>, Andy Gross <agross@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Doug Anderson <dianders@chromium.org>,
"Mathias Nyman" <mathias.nyman@intel.com>,
<devicetree@vger.kernel.org>, <linux-arm-msm@vger.kernel.org>,
<linux-usb@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
<linux-pm@vger.kernel.org>, <quic_ppratap@quicinc.com>,
<quic_vpulyala@quicinc.com>
Subject: Re: [PATCH v20 2/5] usb: dwc3: core: Host wake up support from system suspend
Date: Tue, 28 Jun 2022 11:01:48 +0530 [thread overview]
Message-ID: <20220628053148.GA21797@hu-pkondeti-hyd.qualcomm.com> (raw)
In-Reply-To: <CAE-0n52bq9feA6BVdAp791SWQtT1Yj4M2ppg3o_KOaRFO8r+0Q@mail.gmail.com>
On Mon, Jun 27, 2022 at 01:02:49PM -0700, Stephen Boyd wrote:
> Quoting Pavan Kondeti (2022-06-20 01:54:15)
> > +Felipe, Bjorn
> >
> > On Thu, Jun 16, 2022 at 10:15:49AM -0700, Matthias Kaehlcke wrote:
> > > On Thu, Jun 16, 2022 at 02:41:10PM +0530, Pavan Kondeti wrote:
> > >
> > > Good point! It doesn't really ensure that the child is probed (actually it
> > > won't be probed and DL_FLAG_AUTOPROBE_CONSUMER doesn't make sense here), it
> > > could happen that dwc3_qcom_probe() is deferred multiple times, but eventually
> > > the PHYs should be ready and dwc3_probe() be invoked through
> > > of_platform_populate().
> >
> > This is a generic problem i.e if a parent can only proceed after the child
> > devices are bounded (i.e probed successfully), how to ensure this behavior
> > from the parent's probe? Since we can't block the parent probe (async probe is
> > not the default behavior), we have to identify the condition that the children
> > are deferring probe, so that parent also can do that.
> >
> > Can we add a API in drivers core to tell if a device probe is deferred or
> > not? This can be done by testing list_empty(&dev->p->deferred_probe) under
> > deferred_probe_mutex mutex. The parent can return EPROBE_DEFER based on this
> > API return value.
> >
> > Another alternative would be explicitly checking if the child device suppliers
> > are ready or not before adding child device. That would require decoupling
> > of_platform_populate() to creating devices and adding devices.
> >
> > Note that this problem is not just limited to suppliers not ready. if the
> > dwc3-qcom is made asynchronous probe, then its child also probed
> > asynchronously and there is no guarantee that child would be probed by the
> > time of_platform_populate() is returned. The bus notifier might come handy
> > in this case. The parent can register for this notifier and waiting for
> > the children device's BUS_NOTIFY_BOUND_DRIVER/BUS_NOTIFY_DRIVER_NOT_BOUND
> > notifications. This would also work in our case, if we move to
> > of_platform_populate() outside the probe().
> >
> > Would like to hear other people thoughts on this.
> >
>
> I'm not following very closely but it sounds like a problem that may be
> solved by using the component driver code (see
> include/linux/component.h). That would let you move anything that needs
> to be done once the child devices probe to the aggregate driver 'bind'
> function (see struct component_master_ops::bind).
Thanks Stephen for letting us know about the component device framework.
IIUC,
- dwc3-qcom (parent of the dwc3 core) registers as a component master by
calling component_master_add_with_match() before calling
of_platform_populate(). The match callback could be as simple as comparing
the device against our child device.
- The dwc3 core (child) at the end of its probe can add as a component by calling
component_add().
- The above triggers the component_master_ops::bind callback implemented in
dwc3-qcom driver which signals that we are good to go.
- The dwc-qcom can call component_bind_all() to finish the formality i.e
telling the dwc3 core that we are good to go.
Is my understanding correct? This is what we are looking for i.e a way for
the child device(s) to signal the parent when the former is bounded.
Also what happens when the child device probe fails for any reason. i.e
component_add() would never be called so the master driver i.e dwc3-qcom would
wait indefinitely. May be it needs to implement a timeout or runtime suspend
etc should take care of keeping the resoures in suspend state.
Thanks,
Pavan
next prev parent reply other threads:[~2022-06-28 5:32 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-02 8:24 [PATCH v20 0/5] USB DWC3 host wake up support from system suspend Krishna Kurapati
2022-06-02 8:24 ` [PATCH v20 1/5] dt-bindings: usb: dwc3: Add wakeup-source property support Krishna Kurapati
2022-06-02 8:24 ` [PATCH v20 2/5] usb: dwc3: core: Host wake up support from system suspend Krishna Kurapati
2022-06-02 19:35 ` Matthias Kaehlcke
2022-06-06 20:45 ` Matthias Kaehlcke
2022-06-13 18:08 ` Matthias Kaehlcke
2022-06-14 17:53 ` Matthias Kaehlcke
2022-06-14 19:37 ` Krishna Kurapati PSSNV
2022-06-16 9:11 ` Pavan Kondeti
2022-06-16 17:15 ` Matthias Kaehlcke
2022-06-20 8:54 ` Pavan Kondeti
2022-06-23 18:38 ` Matthias Kaehlcke
2022-06-24 8:58 ` Pavan Kondeti
2022-06-27 20:02 ` Stephen Boyd
2022-06-28 5:31 ` Pavan Kondeti [this message]
2022-06-29 22:15 ` Stephen Boyd
2022-06-30 18:13 ` Krishna Kurapati PSSNV
2022-07-01 1:10 ` Matthias Kaehlcke
2022-07-01 10:15 ` Pavan Kondeti
2022-07-01 15:52 ` Matthias Kaehlcke
[not found] ` <09f6a717-2bbb-6bd3-f7a8-5ac9e3db51f3@quicinc.com>
[not found] ` <9f9f9abc-9b37-8bfb-3efa-6c860b5dba8d@quicinc.com>
2022-07-13 1:34 ` Matthias Kaehlcke
2022-06-02 8:24 ` [PATCH v20 3/5] usb: dwc3: qcom: Add helper functions to enable,disable wake irqs Krishna Kurapati
2022-06-02 8:24 ` [PATCH v20 4/5] usb: dwc3: qcom: Configure wakeup interrupts during suspend Krishna Kurapati
2022-06-02 13:07 ` Pavan Kondeti
2022-06-02 8:24 ` [PATCH v20 5/5] usb: dwc3: qcom: Keep power domain on to retain controller status Krishna Kurapati
2022-06-02 13:07 ` Pavan Kondeti
2022-06-02 13:09 ` [PATCH v20 0/5] USB DWC3 host wake up support from system suspend Pavan Kondeti
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