linux-kernel - Re: [PATCH v2 2/2] phy: qcom-usb-hs: Add qcom,dp-manual-pullup logic

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Date:   Thu, 29 Dec 2022 22:02:52 +0100
From:   Stephan Gerhold <stephan@...hold.net>
To:     Bryan O'Donoghue <bryan.odonoghue@...aro.org>
Cc:     agross@...nel.org, andersson@...nel.org, vkoul@...nel.org,
        kishon@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, konrad.dybcio@...aro.org,
        linux-arm-msm@...r.kernel.org, linux-phy@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH v2 2/2] phy: qcom-usb-hs: Add qcom,dp-manual-pullup logic

On Thu, Dec 29, 2022 at 08:45:15PM +0100, Stephan Gerhold wrote:
> On Thu, Dec 29, 2022 at 06:34:10PM +0000, Bryan O'Donoghue wrote:
> > Downstream has a flag called qcom,dp-manual-pullup which informs the
> > downstream driver if it should toggle ULPI_MISC_A_VBUSVLDEXTSEL and
> > ULPI_MISC_A_VBUSVLDEXT.
> > 
> > Downstream states:
> > 
> > "qcom,dp-manual-pullup: If present, vbus is not routed to USB
> >         controller/phy and controller driver therefore enables pull-up
> >         explicitly before starting controller using usbcmd run/stop bit."
> > 
> > Working with a system that has both an external Type-C port controller and
> > an internal USB Hub results in a situation where VBUS is not connected to
> > the SoC.
> > 
> > In this case we still need to set the DP pullup.
> > 
> > This patch enables and disables the DP pullup on PHY power_on and power_off
> > respectively if the DT has declared the bool "qcom,enable-vbus-pullup"
> > effectively replicating the downstream logic to the same effect.
> > 
> > Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
> [...]
> 
> An alternative that I've occasionally used for early bring-up is to
> simply use a dummy extcon driver [1] that permanently reports active
> VBUS. The end result is the same. While it's clearly a hack perhaps this
> makes it a bit more clear that ideally you really should try to assign
> an extcon device, to avoid keeping the USB controller and PHY on
> permanently.
> 

BTW another nice trick that should work in all almost all cases is to
use the state of the PMIC USB_IN pin as VBUS detection. All battery-
powered devices I have seen route the USB VBUS to PM8916 USB_IN. And
even many boards like DB410c seem to do that or at least permanently
supply 5V there. In all these cases the &pm8916_usbin extcon will
report a VBUS state that should make USB work.

Have you tried using that on your MSM8939 board with the Type-C setup?

&pm8916_usbin {
	status = "okay";
};

&usb {
	status = "okay";
	usb-role-switch;
	extcon = <&pm8916_usbin>;
};

&usb_hs_phy {
	extcon = <&pm8916_usbin>;
};

Stephan