linux-kernel - Re: [PATCH v3] usb: dwc3: qcom: Remove extcon functionality from glue

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Message-ID: <c13af350-3036-4b80-bfa9-0c3f02886fc5@oss.qualcomm.com>
Date: Wed, 16 Jul 2025 13:24:14 +0530
From: Krishna Kurapati <krishna.kurapati@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        Bjorn Andersson <bjorn.andersson@....qualcomm.com>,
        linux-arm-msm@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] usb: dwc3: qcom: Remove extcon functionality from glue



On 7/15/2025 11:31 PM, Dmitry Baryshkov wrote:
> On Tue, Jul 15, 2025 at 07:47:20PM +0200, Greg Kroah-Hartman wrote:
>> On Mon, Jul 14, 2025 at 10:17:02AM +0530, Krishna Kurapati wrote:
>>> Deprecate usage of extcon functionality from the glue driver. Now
>>> that the glue driver is a flattened implementation, all existing
>>> DTs would eventually move to new bindings. While doing so let them
>>> make use of role-switch/ typec frameworks to provide role data
>>> rather than using extcon.
>>

Hi Greg,

  Thanks for the comments. We wanted the users of these new bindings to 
start using role switch instead of extcon.

>> "Deprecate"?  Looks like you are just deleting all of this code, what is
>> going to break when this is removed?  Are there any in-kernel users of
>> it?

Currently, there are no in-kernel users of this new bindings using extcon.

>>
>>> On upstream, summary of targets/platforms using extcon is as follows:
>>>
>>> 1. MSM8916 and MSM8939 use Chipidea controller, hence the changes have no
>>> effect on them.
>>
>> Ok, so those are fine, but:
>>
>>> 2. Of the other extcon users, most of them use "linux,extcon-usb-gpio"
>>> driver which relies on id/vbus gpios to inform role changes. This can be
>>> transitioned to role switch based driver (usb-conn-gpio) while flattening
>>> those platforms to move away from extcon and rely on role
>>> switching.
>>
>> When is that going to happen?  Where are those patches?
> 
> This should be better explained in the commit message, I agree here.
> 
> Krishna, please point out that existing extcon platforms use legacy glue
> driver (due to using legacy DT bindings), while this patch touches only
> the new ("flattened") DWC3 driver.
> 

Sure, will add it to commit message saying that there are no in-kernel 
extcon users of new bindings.

>>
>>> 3. The one target that uses dwc3 controller and extcon and is not based
>>> on reading gpios is "arch/arm64/boot/dts/qcom/msm8996-xiaomi-common.dtsi".
>>> This platform uses TI chip to provide extcon. If usb on this platform is
>>> being flattneed, then effort should be put in to define a usb-c-connector
>>> device in DT and make use of role switch functionality in TUSB320L driver.
>>
>> Again, when is that going to be changed?  We can't break in-kernel users
>> :(
>>

I think if someone is updating the bindings to flattened implementation, 
they need to use Type-C and role switching framework instead of extcon 
since this chip is a Typec port controller one.

Regards,
Krishna,