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

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Date: Mon, 3 Jun 2024 17:25:38 +0900
From: Jung Daehwan <dh10.jung@...sung.com>
To: Krzysztof Kozlowski <krzk@...nel.org>
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 Mon, Jun 03, 2024 at 08:58:10AM +0200, Krzysztof Kozlowski wrote:
> 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.
> 

This issue is not specific on SoC side but dwc3 controller. I think it's
better to add it to dwc3 directly but I can't find dts for dwc3. Dts for
SoC, which uses dwc3 would be needed in this case, right?

Best Regards,
Jung Daehwan

> Best regards,
> Krzysztof
> 
>