linux-kernel - Re: [PATCH] usb: dwc3: core: modify IO memory resource after deferred probe completes

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Message-ID: <20130725205224.GA12209@radagast>
Date:	Thu, 25 Jul 2013 23:52:24 +0300
From:	Felipe Balbi <balbi@...com>
To:	Paul Zimmerman <Paul.Zimmerman@...opsys.com>
CC:	"Ivan T. Ivanov" <iivanov@...sol.com>,
	"balbi@...com" <balbi@...com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: dwc3: core: modify IO memory resource after
 deferred probe completes

Hi,

On Thu, Jul 25, 2013 at 07:46:58PM +0000, Paul Zimmerman wrote:
> > diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c
> > index 607bef8..50c833f 100644
> > --- a/drivers/usb/dwc3/core.c
> > +++ b/drivers/usb/dwc3/core.c
> > @@ -384,21 +384,6 @@ static int dwc3_probe(struct platform_device *pdev)
> >  		dev_err(dev, "missing memory resource\n");
> >  		return -ENODEV;
> >  	}
> > -	dwc->xhci_resources[0].start = res->start;
> > -	dwc->xhci_resources[0].end = dwc->xhci_resources[0].start +
> > -					DWC3_XHCI_REGS_END;
> > -	dwc->xhci_resources[0].flags = res->flags;
> > -	dwc->xhci_resources[0].name = res->name;
> > -
> > -	res->start += DWC3_GLOBALS_REGS_START;
> > -
> > -	 /*
> > -	  * Request memory region but exclude xHCI regs,
> > -	  * since it will be requested by the xhci-plat driver.
> > -	  */
> > -	regs = devm_ioremap_resource(dev, res);
> > -	if (IS_ERR(regs))
> > -		return PTR_ERR(regs);
> > 
> >  	if (node) {
> >  		dwc->maximum_speed = of_usb_get_maximum_speed(node);
> > @@ -452,6 +437,22 @@ static int dwc3_probe(struct platform_device *pdev)
> >  		return -EPROBE_DEFER;
> >  	}
> > 
> > +	dwc->xhci_resources[0].start = res->start;
> > +	dwc->xhci_resources[0].end = dwc->xhci_resources[0].start +
> > +					DWC3_XHCI_REGS_END;
> > +	dwc->xhci_resources[0].flags = res->flags;
> > +	dwc->xhci_resources[0].name = res->name;
> > +
> > +	res->start += DWC3_GLOBALS_REGS_START;
> 
> Ick. The driver is modifying the struct resource passed to it by the

heh...

> platform code? That seems like a layering violation, and is fragile as
> hell. In addition to this bug, what would happen if the struct resource
> was declared 'const'?

nothing would happen if it was declared const since platform_add_device
makes a copy of what was declared, and that's always non-const.

Also, this is not *modifying* what was passed, just skipping the xHCI
address space so we don't request_mem_region() an area we won't really
handle and prevent xhci-hcd.ko from probing.

-- 
balbi

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