linux-kernel - Re: [PATCH v8 6/6] usb: dwc3: qcom: Keep power domain on to support wakeup

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Date:   Mon, 28 Jun 2021 14:23:56 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Sandeep Maheswaram <sanm@...eaurora.org>
Cc:     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>,
        linux-arm-msm@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Pratham Pratap <prathampratap@...eaurora.org>
Subject: Re: [PATCH v8 6/6] usb: dwc3: qcom: Keep power domain on to support
 wakeup

On Mon, Jun 28, 2021 at 05:38:17PM +0530, Sandeep Maheswaram wrote:
> If wakeup capable devices are connected to the controller (directly
> or through hubs) at suspend time keep the power domain on in order
> to support wakeup from these devices.
> 
> Signed-off-by: Sandeep Maheswaram <sanm@...eaurora.org>
> ---
> Checking phy_power_off flag instead of usb_wakeup_enabled_descendants 
> to keep gdsc active.
> 
>  drivers/usb/dwc3/dwc3-qcom.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/dwc3-qcom.c b/drivers/usb/dwc3/dwc3-qcom.c
> index 82125bc..ba31aa3 100644
> --- a/drivers/usb/dwc3/dwc3-qcom.c
> +++ b/drivers/usb/dwc3/dwc3-qcom.c
> @@ -17,6 +17,7 @@
>  #include <linux/of_platform.h>
>  #include <linux/platform_device.h>
>  #include <linux/phy/phy.h>
> +#include <linux/pm_domain.h>
>  #include <linux/usb/of.h>
>  #include <linux/reset.h>
>  #include <linux/iopoll.h>
> @@ -355,9 +356,15 @@ static int dwc3_qcom_suspend(struct dwc3_qcom *qcom)
>  	u32 val;
>  	int i, ret;
>  
> +	struct dwc3 *dwc = platform_get_drvdata(qcom->dwc3);
> +	struct generic_pm_domain *genpd = pd_to_genpd(qcom->dev->pm_domain);
> +
>  	if (qcom->is_suspended)
>  		return 0;
>  
> +	if (!dwc->phy_power_off && dwc->xhci)
> +		genpd->flags |= GENPD_FLAG_ACTIVE_WAKEUP;
> +
>  	val = readl(qcom->qscratch_base + PWR_EVNT_IRQ_STAT_REG);
>  	if (!(val & PWR_EVNT_LPM_IN_L2_MASK))
>  		dev_err(qcom->dev, "HS-PHY not in L2\n");
> @@ -382,9 +389,15 @@ static int dwc3_qcom_resume(struct dwc3_qcom *qcom)
>  	int ret;
>  	int i;
>  
> +	struct dwc3 *dwc = platform_get_drvdata(qcom->dwc3);
> +	struct generic_pm_domain *genpd = pd_to_genpd(qcom->dev->pm_domain);
> +
>  	if (!qcom->is_suspended)
>  		return 0;
>  
> +	if (dwc->xhci)
> +		genpd->flags &= ~GENPD_FLAG_ACTIVE_WAKEUP;
> +
>  	if (device_may_wakeup(qcom->dev))
>  		dwc3_qcom_disable_interrupts(qcom);
>  

This is essentially the same as v7, which Felipe NAKed
(https://patchwork.kernel.org/project/linux-arm-msm/patch/1619586716-8687-6-git-send-email-sanm@codeaurora.org/)

I think Felipe wants to see the handling of the power domain in the
xhci-plat driver. One problem here is that the power domain is owned
by the glue driver. For dwc3 the glue device is the parent of the xHCI
device, this is also the case for some other drivers like histb or
cdns3, but I'm not sure if it is universally true. If it isn't
xhci-plat could only make use of dev->parent->pm_domain for certain
compatible strings.

One could argue that it isn't very clean either if xhci-plat manipulates
a resource of it's parent. At the same time the glue driver isn't
supposed to check for the wakeup capable devices, so I guess some kind
of trade-off needs to be made.