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 01:25:25 +0530
From:   Krishna Kurapati PSSNV <quic_kriskura@...cinc.com>
To:     Johan Hovold <johan@...nel.org>
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 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).
> 
Hi Johan,

   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.

Regards,
Krishna,

>> 2. For this particular case where we are trying to get info on number of
>> ports present (dwc->num_usb2_ports), we can add compatible data for
>> sc8280-mp and provide input to driver telling num ports is 4.
> 
> That may also work as a way to avoid parsing the xhci registers, but I'm
> still not sure why simply counting the PHYs in DT would not work.
> 
> Johan