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SubjectDMABOUNCE in pci-rcar
Hi Magnus,

I noticed during randconfig testing that you enabled DMABOUNCE for the
pci-rcar-gen2 driver as posted in this patch

I didn't see the original post unfortunately, but I fear we have to
revert it and come up with a better solution, as your approach seems
wrong on a number of levels:

* We really don't want any new users of DMABOUNCE on ARM but instead leave
it to the PXA/IXP/SA1100 based platforms using it today.

* If your SoCs have an IOMMU, you should really use it, as that would
give you much better performance than bounce buffers anyway

* If the hardware is so screwed up that you have to use bounce buffers,
use the SWIOTLB code that is reasonably modern.

* The window base and size in the driver should not be hardcoded, as
this is likely not a device specific property but rather an artifact of
how it's connected. Use the standard "dma-ranges" property.

* You should not need your own dma_map_ops in the driver. What you
do there isn't really specific to your host but should live in some
place where it can be shared with other drivers.

* The implementation of the dma_map_ops is wrong: at the very least,
you cannot use the dma_mask of the pci host when translating
calls from the device, since each pci device can have a different
dma mask that is set by the driver if it needs larger or smaller
than 32-bit DMA space.

* The block bounce code can't be enabled if CONFIG_BLOCK is disabled,
this is how I noticed your changes.

* The block layer assumes that it will bounce any highmem pages,
but that isn't necessarily what you want here: if you have 2GB
of lowmem space (CONFIG_VMSPLIT_2G) or more, you will also have
lowmem pages that need bouncing.

* (completely unrelated, I noticed you set up a bogus I/O space
window. Don't do that, you will get get a panic if a device happens
to use it. Not providing an resource should work fine though)

On the bright side, your other changes in the same series all look
good. Thanks especially for sorting out the probe() function, I was
already wondering if we could change that the way you did.


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