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

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Message-ID: <1287c649-de62-c7d8-1c1d-a30ede7505c9@synopsys.com>
Date:   Tue, 26 Apr 2022 01:12:17 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Pavan Kondeti <quic_pkondeti@...cinc.com>,
        Sandeep Maheswaram <quic_c_sanm@...cinc.com>
CC:     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

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.

Thanks,
Thinh

[1] https://lore.kernel.org/linux-usb/0fb179b977cd187f003ae18adf01bccf09d74092.1618014279.git.Thinh.Nguyen@synopsys.com/T/#ma5f7bdf29cf84b5a0077a4a0857ceb5dfe0c8564
[2] https://lore.kernel.org/linux-usb/76ecefd7-d294-485a-1e2b-e5e556e2a3f7@linux.intel.com/#R