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

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Message-ID: <Y64CaOzWZXERrvkz@gerhold.net>
Date:   Thu, 29 Dec 2022 22:11:04 +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 09:05:23PM +0000, Bryan O'Donoghue wrote:
> On 29/12/2022 21:02, Stephan Gerhold wrote:
> > 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
> 
> I checked USBIN before my last email reply.
> 
> Its possible its connected but its not there on the 8939 schematic I have.
> 

Then it doesn't seem to be a particularly complete schematic. :-)
PM8916 definitely has USB_IN pads (pad # N13, P13). :-)