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

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Message-ID: <c4607aa4-7af7-443f-8ccc-aa4fe3ede3cc@quicinc.com>
Date: Thu, 29 Feb 2024 17:23:08 +0530
From: Krishna Kurapati PSSNV <quic_kriskura@...cinc.com>
To: Johan Hovold <johan@...nel.org>
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 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/

Hi Johan. Thanks for the review.

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"

> 
>> +static int dwc3_read_port_info(struct dwc3 *dwc)
>> +{
>> +	void __iomem *base;
>> +	u8 major_revision;
>> +	u32 offset;
>> +	u32 val;
>> +
>> +	/*
>> +	 * Remap xHCI address space to access XHCI ext cap regs since it is
>> +	 * needed to get information on number of ports present.
>> +	 */
>> +	base = ioremap(dwc->xhci_resources[0].start,
>> +		       resource_size(&dwc->xhci_resources[0]));
>> +	if (IS_ERR(base))
>> +		return PTR_ERR(base);
>> +
>> +	offset = 0;
>> +	do {
>> +		offset = xhci_find_next_ext_cap(base, offset,
>> +						XHCI_EXT_CAPS_PROTOCOL);
>> +		if (!offset)
>> +			break;
>> +
>> +		val = readl(base + offset);
>> +		major_revision = XHCI_EXT_PORT_MAJOR(val);
>> +
>> +		val = readl(base + offset + 0x08);
>> +		if (major_revision == 0x03) {
>> +			dwc->num_usb3_ports += XHCI_EXT_PORT_COUNT(val);
>> +		} else if (major_revision <= 0x02) {
>> +			dwc->num_usb2_ports += XHCI_EXT_PORT_COUNT(val);
>> +		} else {
>> +			dev_warn(dwc->dev,
>> +				 "unrecognized port major revision %d\n",
> 
> I still think you should merge this with the previous line even if you
> end up with 83 chars.
> 
>> +							major_revision);
>> +		}
>> +	} while (1);
>   
>> +	/*
>> +	 * 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.

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 thought this statement was fine to go.

> 
>> +	hw_mode = DWC3_GHWPARAMS0_MODE(dwc->hwparams.hwparams0);
>> +	if (hw_mode == DWC3_GHWPARAMS0_MODE_HOST) {
>> +		ret = dwc3_read_port_info(dwc);
>> +		if (ret)
>> +			goto err_disable_clks;
>> +	} else {
>> +		dwc->num_usb2_ports = 1;
>> +		dwc->num_usb3_ports = 1;
>> +	}
> 

Thanks for the review. Can you help let me know your review on the other 
patches as well.

Regards,
Krishna,