linux-kernel - Re: [PATCH v8 6/9] usb: dwc3: qcom: Add multiport controller support for qcom wrapper

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Date:   Thu, 8 Jun 2023 11:44:41 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Krishna Kurapati PSSNV <quic_kriskura@...cinc.com>
Cc:     Bjorn Andersson <andersson@...nel.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        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_wcheng@...cinc.com,
        quic_jackp@...cinc.com, quic_harshq@...cinc.com,
        ahalaney@...hat.com
Subject: Re: [PATCH v8 6/9] usb: dwc3: qcom: Add multiport controller support
 for qcom wrapper

On Thu, Jun 08, 2023 at 01:25:25AM +0530, Krishna Kurapati PSSNV wrote:
> On 6/7/2023 5:14 PM, Johan Hovold wrote:
> > On Fri, May 26, 2023 at 08:55:22PM +0530, Krishna Kurapati PSSNV wrote:
> >> On 5/26/2023 8:25 AM, Bjorn Andersson wrote:
> > 
> >>> We need to fix the dwc3 glue design, so that the glue and the core can
> >>> cooperate - and we have a few other use cases where this is needed (e.g.
> >>> usb_role_switch propagation to the glue code).
> > 
> >>     Thanks for the comments on this patch. I had some suggestions come in
> >> from the team internally:
> >>
> >> 1. To use the notifier call available in drivers/usb/core/notify.c and
> >> make sure that host mode is enabled. That way we can access dwc or xhci
> >> without any issue.
> > 
> > I don't think this is a good idea and instead the callbacks should be
> > dedicated for the xhci and dwc3 drivers. A struct with callbacks can be
> > passed down to the child devices, which call back into the drivers of
> > their parents for notifications and when they need services from them
> > (e.g. during suspend or on role changes).

>    While I agree with you that these notifications are to be used during 
> role switch or suspend/resume, there is no restriction on using them for 
> checking whether we are in host mode or not. IMO, it would be cleaner as 
> we won't be dereferencing dwc driver data at all to check if we are in 
> host mode or not.

I'm not sure I understand what you're saying here. Could you try to
rephrase it?

Johan