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

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Date:	Fri, 26 Jul 2013 23:32:26 +0300
From:	Felipe Balbi <balbi@...com>
To:	Paul Zimmerman <Paul.Zimmerman@...opsys.com>
CC:	"balbi@...com" <balbi@...com>,
	"Ivan T. Ivanov" <iivanov@...sol.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 Fri, Jul 26, 2013 at 06:44:23PM +0000, Paul Zimmerman wrote:
> > From: Felipe Balbi [mailto:balbi@...com]
> > Sent: Friday, July 26, 2013 2:54 AM
> > > > > 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.
> > 
> > gotta try that one... Perhaps the correct way would be to copy the
> > resource to a private struct resource and modify that one, leaving
> > pdev->resources untouched.
> 
> Maybe this is a dumb question, but why can't the driver that is going
> to use the resource after this just "know" that it has to add
> DWC3_GLOBALS_REGS_START to the start address? Are there some versions
> of the core where that is not the case?

that won't work, because dwc3.ko will already have request_mem_region()
the entire region and a subsequent request_mem_region() for xHCI space
only would fail.

> Or, maybe there should be two sets of resources?

maybe we should require two sets of resources, yes... but then there's
no point in having any host initialization whatsoever in dwc3.ko.

-- 
balbi

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