linux-kernel - Re: [PATCH 1/4] dmaengine: dw_dmac: use helper macro module_platform

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Date:	Wed, 10 Oct 2012 15:52:40 +0300
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	balbi@...com
Cc:	viresh kumar <viresh.kumar@...aro.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Vinod Koul <vinod.koul@...el.com>,
	linux-kernel@...r.kernel.org,
	spear-devel <spear-devel@...t.st.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH 1/4] dmaengine: dw_dmac: use helper macro module_platform_driver()

On Wed, Oct 10, 2012 at 3:40 PM, Felipe Balbi <balbi@...com> wrote:
> On Wed, Oct 10, 2012 at 12:21:04PM +0300, Andy Shevchenko wrote:
>> On Wed, Oct 10, 2012 at 12:08 PM, viresh kumar <viresh.kumar@...aro.org> wrote:
>> > On Wed, Oct 10, 2012 at 2:34 PM, Andy Shevchenko
>> > <andriy.shevchenko@...ux.intel.com> wrote:
>> >> On Tue, 2012-10-02 at 14:41 +0300, Andy Shevchenko wrote:
>> >>> From: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
>> >>>
>> >>> Since v3.2 we have nice macro to define the platform driver's init and exit
>> >>> calls. This patch simplifies the dw_dmac driver by using that macro.
>> >>
>> >> Actually we can't do this. It will break initialization of some other
>> >> drivers.
>> >
>> > why?
>>
>> We have spi, i2c and hsuart devices connected to the DMA controller.
>> In case we would like to use DMA we have to have the dw_dmac loaded
>> before them. Currently we have spi driver on subsys_initcall level,
>> and Mika, who is developing it, will change to module_init_call level.
>> However, it will just hide the potential issue. He also tried to use
>> deferred module loading, but we don't know if it's good solution or
>> not, and that solution requires something to stop deferring at some
>> moment.
>>
>> Might be we missed something and there is a better solution.
>
> if they can only work with DMA, they should return -EPROBE_DEFER so
> their probe() function can be called after DMA driver has finished
> probing.

They could work either with DMA or via PIO mode.
How does the driver know when to stop to return -EPROBE_DEFER?

-- 
With Best Regards,
Andy Shevchenko
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