linux-kernel - Re: [PATCH v15 2/9] usb: dwc3: core: Access XHCI address space temporarily to read port info

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Date: Mon, 4 Mar 2024 09:40:56 +0100
From: Johan Hovold <johan@...nel.org>
To: Krishna Kurapati PSSNV <quic_kriskura@...cinc.com>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Wesley Cheng <quic_wcheng@...cinc.com>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
	Felipe Balbi <balbi@...nel.org>, devicetree@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, quic_ppratap@...cinc.com,
	quic_jackp@...cinc.com
Subject: Re: [PATCH v15 2/9] usb: dwc3: core: Access XHCI address space
 temporarily to read port info

On Thu, Feb 29, 2024 at 05:23:08PM +0530, Krishna Kurapati PSSNV wrote:
> On 2/29/2024 3:17 PM, Johan Hovold wrote:
> > On Fri, Feb 16, 2024 at 06:27:49AM +0530, Krishna Kurapati wrote:
> >> Currently Multiport DWC3 controllers are host-only capable.
> > 
> > I already asked you to rephrase this so that it becomes clear that you
> > are describing a property of the current hardware (and similar
> > throughout the series):
> > 
> > 	https://lore.kernel.org/all/ZTI7AtCJWgAnACSh@hovoldconsulting.com/

> IMO, the statement is describing a property unique to current hardware, 
> that "If it is a multiport controller, it is then host-only capable"
> 
> I used the word "Currently" to indicate that "Today, the multiport 
> devices present...". Let me know if there is any ambiguity in the sentence.
> 
> In v13, I wrote:
> "Currently host-only capable DWC3 controllers support Multiport."
> You were right. It was ambiguous as it might refer to even single port 
> controllers.
> 
> So I changed it saying all the DWC3 multiport controllers are host only 
> capable.
> 
> How about:
> 
> "All the DWC3 Multi Port controllers that exist today only support host 
> mode"

That should be clear enough, thanks.

> >> +	/*
> >> +	 * Currently only DWC3 controllers that are host-only capable
> >> +	 * support Multiport.
> >> +	 */
> > 
> > So again, also here, rephrase the comment so that it is clear that you
> > are referring to a property of the current hardware.
> 
> I put the comment this way to indicate that we don't want to check for 
> existence of multiple ports if the controller is not "host-only" 
> capable. We should only check for multport support only if we are 
> host-only capable. I think the statement clearly tells that "check for 
> host-only" configuration before proceeding to check for xhci register reads.

Fair enough, this comment could be considered to apply only to the
implementation. Perhaps the following would be more clear though:

	Currently only DWC3 controllers that are host-only capable
	can have more than one port.

or simply

	Host-only capable controllers can have more than one port.

Both of these also gives a hint that this is a property of the hardware.

> I replied the same on:
> https://lore.kernel.org/all/279a54f2-7260-4270-83c7-d6f5c5ba0873@quicinc.com/
> 
> And since you didn't mention anything else at this part of code in your 
> return reply in:
> https://lore.kernel.org/all/ZTYyXhyZN3jBXEfm@hovoldconsulting.com/

I left in the following quote on purpose in that reply:

	> > Please rephrase accordingly throughout so that this becomes clear.

Johan