linux-kernel - Re: [v15 3/6] usb: dwc3: core: Host wake up support from system suspend

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Date:   Fri, 6 May 2022 08:51:22 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Pavan Kondeti <quic_pkondeti@...cinc.com>
Cc:     Krishna Kurapati PSSNV <quic_kriskura@...cinc.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Doug Anderson <dianders@...omium.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, quic_ppratap@...cinc.com,
        quic_vpulyala@...cinc.com,
        Sandeep Maheswaram <quic_c_sanm@...cinc.com>
Subject: Re: [v15 3/6] usb: dwc3: core: Host wake up support from system
 suspend

On Fri, May 06, 2022 at 10:44:48AM +0530, Pavan Kondeti wrote:
> On Fri, May 06, 2022 at 10:41:01AM +0530, Krishna Kurapati PSSNV wrote:
> > 
> > On 5/6/2022 4:18 AM, Matthias Kaehlcke wrote:
> > >On Thu, May 05, 2022 at 02:26:10PM +0530, Krishna Kurapati wrote:
> > >>From: Sandeep Maheswaram <quic_c_sanm@...cinc.com>
> > >>
> > >>During suspend read the status of all port and set hs phy mode
> > >>based on current speed. Use this hs phy mode to configure wakeup
> > >>interrupts in qcom glue driver.
> > >>
> > >>Check wakeup-source property for dwc3 core node to set the
> > >>wakeup capability. Drop the device_init_wakeup call from
> > >>runtime suspend and resume.
> > >>
> > >>Also check during suspend if any wakeup capable devices are
> > >>connected to the controller (directly or through hubs), if there
> > >>are none set a flag to indicate that the PHY is powered
> > >>down during suspend.
> > >>
> > >>Signed-off-by: Sandeep Maheswaram <quic_c_sanm@...cinc.com>
> > >>Signed-off-by: Krishna Kurapati <quic_kriskura@...cinc.com>
> > >>---
> > >>  drivers/usb/dwc3/core.c | 33 ++++++++++++++++++++-------------
> > >>  drivers/usb/dwc3/core.h |  4 ++++
> > >>  drivers/usb/dwc3/host.c | 24 ++++++++++++++++++++++++
> > >>  3 files changed, 48 insertions(+), 13 deletions(-)
> > >>
> > >>diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> > >>index 950e238..cf377f5 100644
> > >>--- a/drivers/usb/dwc3/core.c
> > >>+++ b/drivers/usb/dwc3/core.c
> > >>@@ -33,6 +33,7 @@
> > >>  #include <linux/usb/gadget.h>
> > >>  #include <linux/usb/of.h>
> > >>  #include <linux/usb/otg.h>
> > >>+#include <linux/usb/hcd.h>
> > >This is not needed anymore
> > >
> > >>  #include "core.h"
> > >>  #include "gadget.h"
> > >>@@ -1787,6 +1788,7 @@ static int dwc3_probe(struct platform_device *pdev)
> > >>  	platform_set_drvdata(pdev, dwc);
> > >>  	dwc3_cache_hwparams(dwc);
> > >>+	device_init_wakeup(&pdev->dev, of_property_read_bool(dev->of_node, "wakeup-source"));
> > >>  	spin_lock_init(&dwc->lock);
> > >>  	mutex_init(&dwc->mutex);
> > >>@@ -1936,6 +1938,7 @@ static int dwc3_suspend_common(struct dwc3 *dwc, pm_message_t msg)
> > >>  {
> > >>  	unsigned long	flags;
> > >>  	u32 reg;
> > >>+	struct usb_hcd  *hcd = platform_get_drvdata(dwc->xhci);
> > >This isn't used anymore, delete it
> > My bad, Will fix this in next version.
> > >>  	switch (dwc->current_dr_role) {
> > >>  	case DWC3_GCTL_PRTCAP_DEVICE:
> > >>@@ -1948,10 +1951,7 @@ static int dwc3_suspend_common(struct dwc3 *dwc, pm_message_t msg)
> > >>  		dwc3_core_exit(dwc);
> > >>  		break;
> > >>  	case DWC3_GCTL_PRTCAP_HOST:
> > >>-		if (!PMSG_IS_AUTO(msg)) {
> > >>-			dwc3_core_exit(dwc);
> > >>-			break;
> > >>-		}
> > >>+		dwc3_check_phy_speed_mode(dwc);
> > >>  		/* Let controller to suspend HSPHY before PHY driver suspends */
> > >>  		if (dwc->dis_u2_susphy_quirk ||
> > >>@@ -1967,6 +1967,16 @@ static int dwc3_suspend_common(struct dwc3 *dwc, pm_message_t msg)
> > >>  		phy_pm_runtime_put_sync(dwc->usb2_generic_phy);
> > >>  		phy_pm_runtime_put_sync(dwc->usb3_generic_phy);
> > >>+
> > >>+		if (!PMSG_IS_AUTO(msg)) {
> > >>+			if (device_may_wakeup(dwc->dev) &&
> > >>+					device_wakeup_path(dwc->dev)) {
> > >nit: the indentation is odd, align it with device_may_wakeup()?
> > Sure, Will take care of it.
> > >>+				dwc->phy_power_off = false;
> > >>+			} else {
> > >>+				dwc->phy_power_off = true;
> > >>+				dwc3_core_exit(dwc);
> > >As commented earlier, taking the controller and PHYs completely down causes a
> > >significant power draw in some USB clients. Let's clarify what the specific
> > >benefits are of doing dwc3_core_exit() vs. entering a low power mode.
> > Sure, once we come to a conclusion on this, I will refresh the patches.
> 
> I think, Matthias is asking you to clarify in the commit description. we can
> even quote Matthias observations.

Actually I would like to have a discussion about the benefits of powering down
the controller and PHYs vs. entering a low power state. Maybe there are good
reasons for powering everything down (e.g. significant power savings), but
as we have seen there are also significant downsides, so let's make sure
we understand both.