linux-kernel - Re: [PATCH 1/6] dt-bindings: usb: dwc3: Clean up hs_phy

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Message-ID: <ZWW_FOAKp95Cf9vN@hovoldconsulting.com>
Date:   Tue, 28 Nov 2023 11:21:08 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Krishna Kurapati PSSNV <quic_kriskura@...cinc.com>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, quic_wcheng@...cinc.com,
        linux-arm-msm@...r.kernel.org, linux-usb@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        quic_ppratap@...cinc.com, quic_jackp@...cinc.com
Subject: Re: [PATCH 1/6] dt-bindings: usb: dwc3: Clean up hs_phy_irq in
 bindings

On Fri, Nov 24, 2023 at 11:09:04PM +0530, Krishna Kurapati PSSNV wrote:
> >> Yes. From whatever targets I was able to find, only one of them didn't
> >> have the power_event irq. Rest all of them had. I will recheck that
> >> particular one again.
> > 
> > Please do. The driver polls the corresponding status register on all
> > platforms currently, and perhaps this interrupt can one day be used to
> > get rid of the polling.
> >   
> 
> Ok, I just rechecked and case is, I am not able to get my hands on the 
> doc. I can't say for sure that the target is missing the pwr_event 
> interrupt. I say we can safely add the target assuming pwr_event is 
> present for ipq9574. Every target so far even on downstream has this IRQ 
> present in hw.

Ok, good.

> >>> Now if the HS interrupt is truly unusable, I guess we can consider
> >>> dropping it throughout and the above becomes just three permutations
> >>> instead, which can even be expressed along the lines of:
> >>
> >> Infact, I wanted to do this but since you mentioned before that if HW
> >> has it, we must describe it, I kept it in. But since this functionality
> >> is confirmed to be mutually exclusive of qusb2/{dp/dm}, I am aligned to
> >> skip it in bindings and drop it in DT.
> > 
> > As I mentioned elsewhere, it depends on whether it can be used at all.
> > Not simply whether there is some other mechanism that can be used in its
> > stead. Such a decision should be left up to the implementation.
> > 
> > That's why I said "truly unusable" above. It's still not clear to me
> > whether that is the case or not.
> 
> I looked at the code of  4.4, 4.14/ 4.19/ 5.4/ 5.10/ 5.15/ 6.1 and none 
> of them implement the hs_phy_irq.

But again, that is completely irrelevant. As I've said numerous times
now, this is about what the hardware is capable of, not which
functionality a particular OS chooses to use.
 
> My opinion would be to keep the power_event irq as mandatory and not to 
> include the hs_phy_irq.

Ok, but you still need to explain why dropping hs_phy_irq is correct.

Until there's a clear answer to that, it seems we need to include it.

Johan