linux-kernel - Re: [PATCH v4 0/3] Skip phy initialization for DWC3 USB Controllers

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Message-ID: <3c52770a-5a04-99b3-0875-d902142a336c@synopsys.com>
Date:   Fri, 29 Apr 2022 19:10:56 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Pavan Kondeti <quic_pkondeti@...cinc.com>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>
CC:     Sandeep Maheswaram <quic_c_sanm@...cinc.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Felipe Balbi <balbi@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Doug Anderson <dianders@...omium.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        Mathias Nyman <mathias.nyman@...el.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "quic_ppratap@...cinc.com" <quic_ppratap@...cinc.com>,
        "quic_kriskura@...cinc.com" <quic_kriskura@...cinc.com>,
        "quic_vpulyala@...cinc.com" <quic_vpulyala@...cinc.com>
Subject: Re: [PATCH v4 0/3] Skip phy initialization for DWC3 USB Controllers

Pavan Kondeti wrote:
> Hi Thinh,
> 
> On Tue, Apr 26, 2022 at 01:12:17AM +0000, Thinh Nguyen wrote:
>> Hi,
>>
>> Pavan Kondeti wrote:
>>> Hi Mathias,
>>>
>>> On Thu, Apr 21, 2022 at 10:30:52AM +0530, Sandeep Maheswaram wrote:
>>>> Runtime suspend of phy drivers was failing from DWC3 driver as
>>>> runtime usage value is 2 because the phy is initialized from
>>>> DWC3 core and HCD core.
>>>> Some controllers like DWC3 and CDNS3 manage phy in their core drivers.
>>>> This property can be set to avoid phy initialization in HCD core.
>>>>
>>>> v4:
>>>> Added the device tree binding patch in the series.
>>>>
>>>> v3:
>>>> Coming back to this series based on discussion at below thread
>>>> https://urldefense.com/v3/__https://patchwork.kernel.org/project/linux-arm-msm/patch/1648103831-12347-4-git-send-email-quic_c_sanm@quicinc.com/__;!!A4F2R9G_pg!fykTNTBuKk9ci6zKdcuQNbuZQdVi_HekU3jetzud-PQVhbRaVhhZHKz0k_LfG0cgwaX4bQM5bLI0ep6tYyikgvYK7b5SdA$ 
>>>> Dropped the dt bindings PATCH 1/3 in v2
>>>> https://urldefense.com/v3/__https://patchwork.kernel.org/project/linux-arm-msm/cover/1636353710-25582-1-git-send-email-quic_c_sanm@quicinc.com/__;!!A4F2R9G_pg!fykTNTBuKk9ci6zKdcuQNbuZQdVi_HekU3jetzud-PQVhbRaVhhZHKz0k_LfG0cgwaX4bQM5bLI0ep6tYyikgva2VXahOQ$  
>>>>
>>>> v2:
>>>> Updated the commit descriptions.
>>>> Changed subject prefix from dwc to dwc3.
>>>> Increased props array size.
>>>>
>>>>
>>>> Sandeep Maheswaram (3):
>>>>   dt-bindings: usb: usb-xhci: Add bindings for usb-skip-phy-init
>>>>     property
>>>>   usb: host: xhci-plat: Add device property to set XHCI_SKIP_PHY_INIT
>>>>     quirk
>>>>   usb: dwc3: host: Set the property usb-skip-phy-init
>>>>
>>>>  Documentation/devicetree/bindings/usb/usb-xhci.yaml | 4 ++++
>>>>  drivers/usb/dwc3/host.c                             | 4 +++-
>>>>  drivers/usb/host/xhci-plat.c                        | 3 +++
>>>>  3 files changed, 10 insertions(+), 1 deletion(-)
>>>>
>>>
>>> This is the latest series with bindings added as per Greg's comment. Can you
>>> please pick up this series if you don't have any further comments.
>>>
>>
>> We've had this conversation going on for a while. Seems there's no good
>> one solution with everyone fully getting on-board.
>>
>> I've tried to get some of the quirks out before also, but ran into the
>> same problem. [1]
>>
>> As Mathias noted [2] before, maybe we can create a new xhci-snps
>> platform glue driver.
>>
>> The problem with the current implementation is passing dwc3's related
>> info to xhci-plat generic driver is very clunky. We can teach the new
>> glue driver with all the info necessary to drive the controller.
>>
>> We can just pass the controller's version (and subversion) as a property
>> for platform device. This way, we can:
>>
>> 1) Separate the quirks from xhci-plat glue. Most common quirks can be
>> detected just base on the controller's version
>>
>> 2) Avoid having to create duplicate "snps,*" properties
>>
>> 3) Get access to the common xhci quirk flags while maintain abstraction
>>
>> 4) Potentially add compatibility string as part of the controller's
>> version and let the glue driver handle the rest
>>
>> 5) Reduce introducing new "quirks" in the future
>>
>> I can get started with this. Let me know if you have any comment.
> 
> Sorry, could not reply earlier. The proposal sounds good to me.
> 
> The xhci-plat is a thin wrapper, so having a separate wrapper for SNPS
> controller is definitely not an overkill and gives lot of flexibility
> in abstracting dwc3 specifics. Also dwc3/host.c becomes just a platform
> device creation wrapper and xHC specifics are completely taken out.
> 

Sure. I'll be away for a few weeks and come back by the end of May. I
can do that then.

Thanks,
Thinh