linux-kernel - Re: [PATCH v13 05/10] usb: dwc3: qcom: Refactor IRQ handling in QCOM Glue driver

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Date:   Fri, 10 Nov 2023 10:28:25 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Wesley Cheng <quic_wcheng@...cinc.com>
Cc:     Krishna Kurapati PSSNV <quic_kriskura@...cinc.com>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Andy Gross <agross@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Felipe Balbi <balbi@...nel.org>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, quic_pkondeti@...cinc.com,
        quic_ppratap@...cinc.com, quic_jackp@...cinc.com,
        ahalaney@...hat.com, quic_shazhuss@...cinc.com
Subject: Re: [PATCH v13 05/10] usb: dwc3: qcom: Refactor IRQ handling in QCOM
 Glue driver

On Thu, Nov 09, 2023 at 12:25:59PM -0800, Wesley Cheng wrote:

> > > > Since the DeviceTree passed to the OS, should describe the hardware to
> > > > the OS, and should represent the hardware from the point-of-view of the
> > > > OS, adding one interrupt (ctrl_irq[0]) might be sufficient as Linux
> > > > would not use the other interrupts.
> > > 
> > > I've only skimmed the virtualisation bits in xHCI spec, but it seems
> > > Linux as VMM would still be involved in assigning these interrupts to
> > > VMs.

> IMO it might be a bit premature to add definitions for how to utilize
> secondary interrupters since design wise, there's nothing really too well
> defined yet.  At least for the XHCI path, we will have a slew of potential
> use cases for secondary interrupters, such as USB audio offloading, or for
> VMMs, etc...  I've only heard mentions about some of them after pushing the
> usb audio offloading series, but I don't have much details on it.

I tend to agree.

> > > This may possibly be something that we can ignore for now, but perhaps
> > > someone more familiar with the hardware, like Thinh, can chime in.

> > > You need to get into the same mindset when it comes to devicetree. Even
> > > if Linux currently does not use an interrupt, like the pwr_event_irq,
> > > you should still add it so that when/if someone implements support for
> > > it, an older platform using the original dt may also take advantage of
> > > it.
> 
> Yeah, I totally agree with this point, but I'm not sure if adding it into
> the "interrupts" array is the way to go.  It would probably have to change
> as support is added.

Yes, that in itself would probably not be sufficient and possibly not
even correct.

> Sorry for jumping in, but just giving my two cents since I'm the one trying
> to do the initial push for the support for secondary interrupters :).

Appreciate your input.

Johan