linux-kernel - Re: [PATCH 1/6] dt-bindings: usb: dwc3: Clean up hs_phy

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Message-ID: <004ddc69-1566-4de4-b260-0fca96a9395f@quicinc.com>
Date:   Fri, 24 Nov 2023 23:09:04 +0530
From:   Krishna Kurapati PSSNV <quic_kriskura@...cinc.com>
To:     Johan Hovold <johan@...nel.org>
CC:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, <quic_wcheng@...cinc.com>,
        <linux-arm-msm@...r.kernel.org>, <linux-usb@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <quic_ppratap@...cinc.com>, <quic_jackp@...cinc.com>
Subject: Re: [PATCH 1/6] dt-bindings: usb: dwc3: Clean up hs_phy_irq in
 bindings


>>
>> Yes. From whatever targets I was able to find, only one of them didn't
>> have the power_event irq. Rest all of them had. I will recheck that
>> particular one again.
> 
> Please do. The driver polls the corresponding status register on all
> platforms currently, and perhaps this interrupt can one day be used to
> get rid of the polling.
>   

Ok, I just rechecked and case is, I am not able to get my hands on the 
doc. I can't say for sure that the target is missing the pwr_event 
interrupt. I say we can safely add the target assuming pwr_event is 
present for ipq9574. Every target so far even on downstream has this IRQ 
present in hw.

>>> Note that DP comes before DM above as that seems like the natural order
>>> of these (plus before minus).
>>>
>>> Now if the HS interrupt is truly unusable, I guess we can consider
>>> dropping it throughout and the above becomes just three permutations
>>> instead, which can even be expressed along the lines of:
>>
>> Infact, I wanted to do this but since you mentioned before that if HW
>> has it, we must describe it, I kept it in. But since this functionality
>> is confirmed to be mutually exclusive of qusb2/{dp/dm}, I am aligned to
>> skip it in bindings and drop it in DT.
> 
> As I mentioned elsewhere, it depends on whether it can be used at all.
> Not simply whether there is some other mechanism that can be used in its
> stead. Such a decision should be left up to the implementation.
> 
> That's why I said "truly unusable" above. It's still not clear to me
> whether that is the case or not.
> 

I looked at the code of  4.4, 4.14/ 4.19/ 5.4/ 5.10/ 5.15/ 6.1 and none 
of them implement the hs_phy_irq.

>>> 	- anyOf:
>>> 	  - items:
>>> 	    - const: qusb2_phy
>>> 	  - items:
>>> 	    - const: dp_hs_phy_irq
>>> 	    - const: dm_hs_phy_irq
>>> 	- const: pwr_event
>>> 	- const: ss_phy_irq	(optional)
>>>
>>
>> This must cover all cases AFAIK. How about we keep pwr_event also
>> optional for time being. The ones I am not able to find also would come
>> up under still binding block.
> 
> No, we should avoid that if we can as with two many optional things,
> these quickly gets messy (one optional interrupt at the end is fine and
> can be expressed using min/maxItems).
> 
> If the "qusb2+" combination above isn't needed, then we're down to four
> permutations, which is few enough to be spelled out explicitly even if
> we decide that the hs_phy_irq should be kept in. Without hs_phy_irq, it
> seems there's really only two permutations.
> 

My opinion would be to keep the power_event irq as mandatory and not to 
include the hs_phy_irq.

Regards,
Krishna,