linux-kernel - A proposal to check the device in generic way

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Date:	Mon, 11 Mar 2013 11:32:31 +0000
From:	"Shevchenko, Andriy" <andriy.shevchenko@...el.com>
To:	linux-kernel <linux-kernel@...r.kernel.org>,
	"Koul, Vinod" <vinod.koul@...el.com>,
	Arnd Bergmann <arnd.bergmann@...aro.org>
CC:	Viresh Kumar <viresh.kumar@...aro.org>,
	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: A proposal to check the device in generic way

Hello.

Currently in linux-next we have the following things:

$ git grep -n 'chan->device->dev->driver' drivers/dma/

drivers/dma/amba-pl08x.c:1594:  if (chan->device->dev->driver !=
&pl08x_amba_driver.drv)
drivers/dma/dmaengine.c:190:    return chan->device->dev->driver->owner;
drivers/dma/edma.c:609: if (chan->device->dev->driver ==
&edma_driver.driver) {
drivers/dma/omap-dma.c:654:     if (chan->device->dev->driver ==
&omap_dma_driver.driver) {
drivers/dma/pl330.c:2374:       if (chan->device->dev->driver !=
&pl330_driver.drv)
drivers/dma/sa11x0-dma.c:1080:  if (chan->device->dev->driver ==
&sa11x0_dma_driver.driver) 

I think it's a non-generic way to check which driver provides a channel
into filter function. First of all, I don't get why that comparison goes
as deep as driver structure. Isn't clearer to check chan->device->dev
against the struct dev passed in the custom parameter structure? Like:

struct filter_params {
 struct dev *dev;
 void *param;
};

bool filter_fn(struct dma_chan *chan, void *fparams)
{
  struct filter_params *p = fparams;
  if (chan->device->dev != p->dev)
   return false;
 ...
}

In case my idea has a right to live, what about to move such check inside
DMA engine code?

Opinions, comments?

Earlier I tried to discuss this with Arnd here: http://www.spinics.net/lists/arm-kernel/msg220716.html

-- 
Andy Shevchenko <andriy.shevchenko@...el.com>
Intel Finland Oy

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