linux-kernel - Re: [PATCH v2 3/5] dt-bindings: usb: xhci: Add 'write-64-hi-lo-quirk' quirk

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Message-ID: <69c954ce-d7a2-420c-b3f6-72caee02d84f@kernel.org>
Date: Mon, 3 Jun 2024 08:58:10 +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 3/5] dt-bindings: usb: xhci: Add 'write-64-hi-lo-quirk'
 quirk

On 03/06/2024 05:34, Jung Daehwan wrote:
> On Fri, May 31, 2024 at 10:12:03AM +0200, Krzysztof Kozlowski wrote:
>> On 31/05/2024 08:07, Daehwan Jung wrote:
>>> xHCI specification 5.1 "Register Conventions" states that 64 bit
>>> registers should be written in low-high order. All writing operations
>>> in xhci is done low-high order following the spec.
>>
>> What is high-low / low-high order? Are you talking about endianness?
>>
> 
> It's not about endianness. It means 64 bit is written by 2 of 32 bit.
> It's when low-high / high-low order is needed.
> 
>>>
>>> Add a new quirk to support workaround for high-low order.
>>
>> Why? If they should be written low-high, then why breaking the spec? Why
>> this cannot be deduced from compatible?
>>
> 
> This quirk is for the controller that has a limitation in supporting
> separate ERSTBA_HI and ERSTBA_LO programming.
> 
> I've copied below from other reply to tell why this is needed.
> 
> 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.
> 
>> Which *upstream* hardware is affected?
>>
> 
> dwc3 and xhci are affected.

Which upstream controllers or SoCs are affected. You did not post any
user of this.

Best regards,
Krzysztof