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

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Date:	Mon, 11 Mar 2013 12:42:40 +0000
From:	"Shevchenko, Andriy" <andriy.shevchenko@...el.com>
To:	Guennadi Liakhovetski <g.liakhovetski@....de>
CC:	linux-kernel <linux-kernel@...r.kernel.org>,
	"Koul, Vinod" <vinod.koul@...el.com>,
	Arnd Bergmann <arnd.bergmann@...aro.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Russell King <linux@....linux.org.uk>
Subject: Re: A proposal to check the device in generic way

On Mon, 2013-03-11 at 13:26 +0100, Guennadi Liakhovetski wrote: 
> > 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;
> > };
> 
> I don't think you always know which DMA device you want to use with this 
> DMA client - sometimes there are several DMA engine devices, that can be 
> used with your DMA client, or even if it's only one, you don't necessarily 
> have a pointer to it in your DMA client.

Ah, right. But let's assume we will use filter_fn in conjunction with
xlate_fn. In that case we will have explicit understanding for which
device we registered specific xlate_fn. So, xlate_fn could provide
struct device pointer to be compared with, though I prefer to have more
suitable mechanism instead of filter_fn.

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