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SubjectRE: [PATCH] usb: dwc3: core: modify IO memory resource after deferred probe completes
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Hi,

On Fri, 2013-07-26 at 02:06 +0000, Paul Zimmerman wrote:
> > From: Felipe Balbi [mailto:balbi@ti.com]
> > Sent: Thursday, July 25, 2013 1:52 PM
> >
> > 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.
>
> OK.
>
> > 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.
>
> Hmm? platform_get_resource() returns a pointer to an entry in the
> platform_device's resource[] array. And "res->start +=" modifies the
> entry pointed at. If it didn't, the bug fixed by this patch wouldn't
> have happened.
>
> Are you sure this code will work OK if you build the driver as a module,
> modprobe it, rmmod it, and then modprobe it again? Seems like it won't,
> unless the dev->resource[] array gets reinitialized in between somehow.

In addition, I think driver is wasting memory, because on every probe
it will reallocate driver state variable. This also happens in several
other drivers which are using deferred probe.

Regards,
Ivan

>
> All this assumes I'm reading the code correctly, of course. If I'm not,
> then never mind :)
>



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