Hello,
On Monday, June 20, 2011 4:33 PM KyongHo Cho wrote:
> On Mon, Jun 20, 2011 at 4:50 PM, Marek Szyprowski
> <m.szyprowski@xxxxxxxxxxx> wrote:
> > +static inline void set_dma_ops(struct device *dev, struct dma_map_ops
> *ops)
> > +{
> > + dev->archdata.dma_ops = ops;
> > +}
> > +
>
> Who calls set_dma_ops()?
> In the mach. initialization part?
Yes, some board, machine or device bus initialization code is supposed to
call this function. Just 'git grep dma_set_ops' and you will see. In my
patch series one of the clients of set_dma_ops function is dmabounce
framework (it is called in dmabounce_register_dev() function).
> What if a device driver does not want to use arch's dma_map_ops
> when machine init procedure set a dma_map_ops?
Could you elaborate on this case? The whole point of dma-mapping framework
is to hide the implementation of DMA mapping operation from the driver.
The driver should never fiddle with dma map ops directly.
> Even though, may arch defiens their dma_map_ops in archdata of device
> structure,
> I think it is not a good idea that is device structure contains a
> pointer to dma_map_ops
> that may not be common to all devices in a board.
It is up to the board/bus startup code to set dma ops correctly.
> I also think that it is better to attach and to detach dma_map_ops
> dynamically.
What's the point of such operations? Why do you want to change dma
mapping methods in runtime?
> Moreover, a mapping is not permanent in our Exynos platform
> because a System MMU may be turned off while runtime.
This is theoretically possible. The System MMU (Samsung IOMMU
controller) driver can change dma_map_ops back to NULL on remove moving
back the client device to generic ARM dma mapping implementation.
> DMA API must come with IOMMU API to initialize IOMMU in runtime.
I don't understand what's the problem here.
Best regards
--
Marek Szyprowski
Samsung Poland R&D Center
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