linux-kernel - Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent dev

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Message-ID: <20160909013743.GB15637@b29397-desktop>
Date:   Fri, 9 Sep 2016 09:37:43 +0800
From:   Peter Chen <hzpeterchen@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Felipe Balbi <balbi@...nel.org>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Russell King - ARM Linux <linux@....linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Sekhar Nori <nsekhar@...com>,
        lkml <linux-kernel@...r.kernel.org>,
        Stuart Yoder <stuart.yoder@....com>,
        Scott Wood <oss@...error.net>,
        David Fisher <david.fisher1@...opsys.com>,
        "Thang Q. Nguyen" <tqnguyen@....com>, Leo Li <pku.leo@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH] usb: dwc3: host: inherit dma configuration from parent
 dev

On Thu, Sep 08, 2016 at 02:52:29PM +0200, Arnd Bergmann wrote:
> On Thursday, September 8, 2016 8:28:10 PM CEST Peter Chen wrote:
> > On Thu, Sep 08, 2016 at 12:17:21PM +0200, Arnd Bergmann wrote:
> > > On Thursday, September 8, 2016 12:43:06 PM CEST Felipe Balbi wrote:
> > > > Arnd Bergmann <arnd@...db.de> writes:
> > > > > On Thursday, September 8, 2016 11:29:04 AM CEST Felipe Balbi wrote:
> > > > If we have a parent device, use that as sysdev, otherwise use self as
> > > > sysdev.
> > > 
> > > But there is often a parent device in DT, as the xhci device is
> > > attached to some internal bus that gets turned into a platform_device
> > > as well, so checking whether there is a parent will get the wrong
> > > device node.
> > 
> > From my point, all platform and firmware information at dwc3 are
> > correct, so we don't need to change dwc3/core.c, only changing for
> > xhci-plat.c is ok.
> 
> Ok, thanks. That leaves the PCI glue, right?

If pci's firmware information can only get from dwc3-pci, I was wrong.
I am almost sure your patch covers all 3 cases. dwc3->sysdev covers
dwc3 core and gadget side, hcd->self.sysdev cover host side. The only
possible improvement may be how to detect pci device.

> 
> > diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c
> > index d2e3f65..563600b 100644
> > --- a/drivers/usb/core/hcd.c
> > +++ b/drivers/usb/core/hcd.c
> > @@ -1118,7 +1118,7 @@ static int register_root_hub(struct usb_hcd *hcd)
> >  		/* Did the HC die before the root hub was registered? */
> >  		if (HCD_DEAD(hcd))
> >  			usb_hc_died (hcd);	/* This time clean up */
> > -		usb_dev->dev.of_node = parent_dev->of_node;
> > +		usb_dev->dev.of_node = parent_dev->sysdev->of_node;
> >  	}
> >  	mutex_unlock(&usb_bus_idr_lock);
> > 
> > At above changes, the root hub's of_node equals to xhci-hcd sysdev's
> > of_node, which is from firmware or from its parent (it is dwc3 core
> > device).
> 
> Just to make sure I understand you right:
> 
> in the qcom,dwc3 -> dwc3 -> xhci hierarchy, this would be the
> dwc3 device, not the qcom,dwc3 device.
> 

Yes, since there is a DT node for dwc3, and firmware information is there,
that's why the original patch (Grygorii Strashko's) can work.

-- 

Best Regards,
Peter Chen