linux-kernel - Re: [PATCH 4/6] usb: cdns3: support power-off of controller when in host role

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Date:   Fri, 17 Nov 2023 10:58:12 +0100
From:   Théo Lebrun <theo.lebrun@...tlin.com>
To:     "Peter Chen" <peter.chen@...nel.org>
Cc:     "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Rob Herring" <robh+dt@...nel.org>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>,
        "Conor Dooley" <conor+dt@...nel.org>,
        "Roger Quadros" <rogerq@...nel.org>,
        "Pawel Laszczak" <pawell@...ence.com>,
        "Nishanth Menon" <nm@...com>,
        "Vignesh Raghavendra" <vigneshr@...com>,
        "Tero Kristo" <kristo@...nel.org>, <linux-usb@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 4/6] usb: cdns3: support power-off of controller when in
 host role

Hello,

On Fri Nov 17, 2023 at 4:38 AM CET, Peter Chen wrote:
> On 23-11-14 12:10:18, Théo Lebrun wrote:
> > Hello,
> > 
> > On Tue Nov 14, 2023 at 9:38 AM CET, Peter Chen wrote:
> > > > +	if (cdns->pdata && cdns->pdata->quirks & CDNS3_RESET_ON_RESUME)
> > > > +		cdns->xhci_plat_data->quirks |= XHCI_RESET_ON_RESUME | XHCI_SUSPEND_RESUME_CLKS;
> > > > +
> > >
> > > If you set this flag, how could you support the USB remote wakeup
> > > request? In that case, the USB bus does not expect re-enumeration.
> > 
> > We didn't support remote USB wakeup. Only S2R mattered in our case and
> > USB remote wakeup wasn't a possibility.
>
> Without this patch, will below be hit for your platform:
>
> 	/* re-initialize the HC on Restore Error, or Host Controller Error */
> 	if (temp & (STS_SRE | STS_HCE)) {
> 		reinit_xhc = true;
> 		if (!xhci->broken_suspend)
> 			xhci_warn(xhci, "xHC error in resume, USBSTS 0x%x, Reinit\n", temp);
> 	}

Yes it hits. The warning as well. How big of an issue is that?

My understanding is that this is the expected behavior with reset on
resume if we don't explicitely pass the flag XHCI_RESET_ON_RESUME. I
don't think we should be having the broken_suspend bit set as its
mentioning some specific quirk on AMD hardware.

Is the only expected difference inbetween having CDNS3_RESET_ON_RESUME &
not having it is resume time? For reference, the status read is 0x411
ie STS_HALT | STS_PCD | STS_SRE. xhc_state is zero.

Regards,

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com