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Commit 4c612add authored by Eugeniy Paltsev's avatar Eugeniy Paltsev Committed by Vineet Gupta
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ARC: dma [non IOC]: fix arc_dma_sync_single_for_(device|cpu) 

ARC backend for dma_sync_single_for_(device|cpu) was broken as it was
not honoring the @dir argument and simply forcing it based on the call:
 - arc_dma_sync_single_for_device(dir) assumed DMA_TO_DEVICE (cache wback)
 - arc_dma_sync_single_for_cpu(dir) assumed DMA_FROM_DEVICE (cache inv)

This is not true given the DMA API programming model and has been
discussed here [1] in some detail.

Interestingly while the deficiency has been there forever, it only started
showing up after 4.17 dma common ops rework, commit a8eb92d0
("arc: fix arc_dma_{map,unmap}_page") which wired up these calls under the
more commonly used dma_map_page API triggering the issue.

[1]: https://lkml.org/lkml/2018/5/18/979


Fixes: commit a8eb92d0 ("arc: fix arc_dma_{map,unmap}_page")
Cc: stable@kernel.org # v4.17+
Signed-off-by: default avatarEugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: default avatarVineet Gupta <vgupta@synopsys.com>
[vgupta: reworked changelog]
parent 6d20caed

arch/arc/mm/dma.c

+47 −2
Original line number Diff line number Diff line
@@ -129,14 +129,59 @@ int arch_dma_mmap(struct device *dev, struct vm_area_struct *vma, 
	return ret;

}



/*

 * Cache operations depending on function and direction argument, inspired by

 * https://lkml.org/lkml/2018/5/18/979

 * "dma_sync_*_for_cpu and direction=TO_DEVICE (was Re: [PATCH 02/20]

 * dma-mapping: provide a generic dma-noncoherent implementation)"

 *

 *          |   map          ==  for_device     |   unmap     ==  for_cpu

 *          |----------------------------------------------------------------

 * TO_DEV   |   writeback        writeback      |   none          none

 * FROM_DEV |   invalidate       invalidate     |   invalidate*   invalidate*

 * BIDIR    |   writeback+inv    writeback+inv  |   invalidate    invalidate

 *

 *     [*] needed for CPU speculative prefetches

 *

 * NOTE: we don't check the validity of direction argument as it is done in

 * upper layer functions (in include/linux/dma-mapping.h)

 */



void arch_sync_dma_for_device(struct device *dev, phys_addr_t paddr,

		size_t size, enum dma_data_direction dir)

{

	switch (dir) {

	case DMA_TO_DEVICE:

		dma_cache_wback(paddr, size);

		break;



	case DMA_FROM_DEVICE:

		dma_cache_inv(paddr, size);

		break;



	case DMA_BIDIRECTIONAL:

		dma_cache_wback_inv(paddr, size);

		break;



	default:

		break;

	}

}



void arch_sync_dma_for_cpu(struct device *dev, phys_addr_t paddr,

		size_t size, enum dma_data_direction dir)

{

	switch (dir) {

	case DMA_TO_DEVICE:

		break;



	/* FROM_DEVICE invalidate needed if speculative CPU prefetch only */

	case DMA_FROM_DEVICE:

	case DMA_BIDIRECTIONAL:

		dma_cache_inv(paddr, size);

		break;



	default:

		break;

	}

}