linux-kernel - Re: [PATCH RESEND 2/2] dt-bindings: usb: add no-64-bit-support property

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Message-ID: <cb247586-6d36-45e4-b5b7-c49b390de406@linaro.org>
Date:   Wed, 1 Nov 2023 12:26:29 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Conor Dooley <conor@...nel.org>, Naveen Kumar <mnkumar@...gle.com>
Cc:     Mathias Nyman <mathias.nyman@...el.com>,
        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>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, royluo@...gle.com,
        devicetree@...r.kernel.org
Subject: Re: [PATCH RESEND 2/2] dt-bindings: usb: add no-64-bit-support
 property

On 01/11/2023 11:38, Conor Dooley wrote:
> On Wed, Nov 01, 2023 at 10:16:25AM +0000, Naveen Kumar wrote:
>> From: Naveen Kumar M <mnkumar@...gle.com>
>>
>> Add a new DT option to specify whether a host controller is able to
>> support 64-bit DMA memory pointers
> 
> What host controllers are broken?
> 
>> Signed-off-by: Naveen Kumar M <mnkumar@...gle.com>
>> ---
>>  Documentation/devicetree/bindings/usb/usb-xhci.yaml | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/usb/usb-xhci.yaml b/Documentation/devicetree/bindings/usb/usb-xhci.yaml
>> index 180a261c3e8f..20dc134004f3 100644
>> --- a/Documentation/devicetree/bindings/usb/usb-xhci.yaml
>> +++ b/Documentation/devicetree/bindings/usb/usb-xhci.yaml
>> @@ -25,6 +25,10 @@ properties:
>>      description: Set if the controller has broken port disable mechanism
>>      type: boolean
>>  
>> +  quirk-no-64-bit-support:
>> +    description: Set if the xHC doesn't support 64-bit DMA memory pointers
> 
> To set this property, you need to know that the host controller is
> broken, so why not just make the driver set the quirk once it sees that
> the host controller is one of the broken ones?
> Unless there are "sometimes broken" host controllers, a dedicated
> property should not be needed, right?

Yep, this looks like property specific to given XHCI controller, thus
can be implied from compatible and there is no need for new DT property
at all.

Also, there is no single DTS user of this property. It looks like you
add it for some out-of-tree vendor or non-upstreamable code, which
personally I would not care about. Feel free to prove me wrong by adding
it to respective DTS in other patchset linked here.

Best regards,
Krzysztof