linux-kernel - Re: [resend][PATCH 01/16] dw_dmac: call .probe after we have a device in place

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Message-ID: <20130109180427.GA13897@intel.com>
Date:	Wed, 9 Jan 2013 20:04:28 +0200
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Vinod Koul <vinod.koul@...el.com>
Cc:	Andy Shevchenko <andy.shevchenko@...il.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.jf.intel.com>,
	linux-kernel@...r.kernel.org,
	Viresh Kumar <viresh.kumar@...aro.org>,
	spear-devel <spear-devel@...t.st.com>
Subject: Re: [resend][PATCH 01/16] dw_dmac: call .probe after we have a
 device in place

On Wed, Jan 09, 2013 at 07:38:48AM -0800, Vinod Koul wrote:
> On Wed, Jan 09, 2013 at 04:56:45PM +0200, Andy Shevchenko wrote:
> > On Wed, Jan 9, 2013 at 3:47 PM, Vinod Koul <vinod.koul@...el.com> wrote:
> > > On Wed, Jan 09, 2013 at 10:17:00AM +0200, Andy Shevchenko wrote:
> > >> If we don't yet have the platform device for the driver when it is being loaded
> > >> we fail to probe the driver. So instead of calling probe() directly we call
> > >> platform_driver_register(). It will call the probe() immediately if we have the
> > >> device but also makes the driver to work on platforms where the platform device
> > >> is created later.
> > > Why wont you have the platform device?
> > 
> > It's still the same device as before. The only difference is in
> > boot/initialization sequence.
> > 
> > > Is this only due to your approach of
> > > creating the device in PCI probe?
> > 
> > No. We had an issue when driver was initialized (and with old version
> > immediately probed)
> > just before it happened in the platform devices. In such case .probe() fails.
> > Above patch makes sure that platform devices are already in the
> > internal structures and we could match them safely.
> hmmm, but that its still not clear why that would happen. Driver init is called
> later when all device creation should already be done.

If the platform device is not yet created (like it might be when it is
enumerated from ACPI for example), the probe fails completely. Certainly
not the situation we want.

Calling platform_driver_register() handles both cases properly.
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