linux-kernel - Re: [PATCH v2 1/5] dt-bindings: usb: snps,dwc3: Add 'snps,xhci-write-64-hi-lo-quirk' quirk

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Date: Tue, 4 Jun 2024 08:19:33 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Jung Daehwan <dh10.jung@...sung.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Thinh Nguyen
 <Thinh.Nguyen@...opsys.com>, Mathias Nyman <mathias.nyman@...el.com>,
 Felipe Balbi <balbi@...nel.org>,
 "open list:USB SUBSYSTEM" <linux-usb@...r.kernel.org>,
 "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
 <devicetree@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/5] dt-bindings: usb: snps,dwc3: Add
 'snps,xhci-write-64-hi-lo-quirk' quirk

On 03/06/2024 10:36, Jung Daehwan wrote:
> On Mon, Jun 03, 2024 at 08:57:16AM +0200, Krzysztof Kozlowski wrote:
>> On 03/06/2024 05:03, Jung Daehwan wrote:
>>> On Fri, May 31, 2024 at 10:10:30AM +0200, Krzysztof Kozlowski wrote:
>>>> On 31/05/2024 08:07, Daehwan Jung wrote:
>>>>> Add a new quirk for dwc3 core to support writing high-low order.
>>>>
>>>> This does not tell me more. Could be OS property as well... please
>>>> describe hardware and provide rationale why this is suitable for
>>>> bindings (also cannot be deduced from compatible).
>>>>
>>>>
>>>
>>> Hi,
>>>
>>> I'm sorry I didn't describe it in dt-bindings patches.
>>> It's described in cover-letter and other patches except in dt-bindings.
>>> I will add it in next submission.
>>>
>>> I've found out the limitation of Synopsys dwc3 controller. This can work
>>> on Host mode using xHCI. A Register related to ERST should be written
>>> high-low order not low-high order. Registers are always written low-high order
>>> following xHCI spec.(64-bit written is done in each 2 of 32-bit)
>>> That's why new quirk is needed for workaround. This quirk is used not in
>>> dwc3 controller itself, but passed to xhci quirk eventually. That's because
>>> this issue occurs in Host mode using xHCI.
>>>
>>
>> If there is only one register then you should just program it
>> differently and it does not warrant quirk property.
>>
> 
> Could you tell me why you think it does not warrant? I think this is
> good to use quirk.

Because it is a fixed case, deduced from compatible. No need for a
property for this.

Best regards,
Krzysztof