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SubjectRe: A proposal to check the device in generic way
Date
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@intel.com>
Intel Finland Oy
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