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: Mon, 3 Jun 2024 12:03:16 +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 1/5] dt-bindings: usb: snps,dwc3: Add
 'snps,xhci-write-64-hi-lo-quirk' quirk

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.

Below are answers from Synopsys support center.

[Synopsys]- The host controller was design to support ERST setting
during the RUN state. But since there is a limitation in controller
in supporting separate ERSTBA_HI and ERSTBA_LO programming,
It is supported when the ERSTBA is programmed in 64bit,
or in 32 bit mode ERSTBA_HI before ERSTBA_LO

[Synopsys]- The internal initialization of event ring fetches
the "Event Ring Segment Table Entry" based on the indication of
ERSTBA_LO written.

Best Regards,
Jung Daehwan

> 
> Best regards,
> Krzysztof
> 
> 
>