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

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Date:	Wed, 10 Oct 2012 16:42:00 +0300
From:	Felipe Balbi <balbi@...com>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
Cc:	balbi@...com, 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()

Hi,

On Wed, Oct 10, 2012 at 03:52:40PM +0300, Andy Shevchenko wrote:
> 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?

Why would you even allow to work as PIO-only ? Who would even want to
use the driver as PIO only ?

In any case, you can add a Kconfig choice like WHATEVER_PIO_ONLY and
only return -EPROBE_DEFER ifndef WHATEVER_PIO_ONLY.

-- 
balbi

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