Commit 2042c352 authored by Balbir Singh's avatar Balbir Singh Committed by Marek Szyprowski
Browse files

dma/mapping.c: dev_dbg support for dma_addressing_limited 

In the debug and resolution of an issue involving forced use of bounce
buffers, 7170130e ("x86/mm/init: Handle the special case of device
private pages in add_pages(), to not increase max_pfn and trigger
dma_addressing_limited() bounce buffers"). It would have been easier
to debug the issue if dma_addressing_limited() had debug information
about the device not being able to address all of memory and thus forcing
all accesses through a bounce buffer. Please see[2]

Implement dev_dbg to debug the potential use of bounce buffers
when we hit the condition. When swiotlb is used,
dma_addressing_limited() is used to determine the size of maximum dma
buffer size in dma_direct_max_mapping_size(). The debug prints could be
triggered in that check as well (when enabled).

Link: https://lore.kernel.org/lkml/20250401000752.249348-1-balbirs@nvidia.com/ [1]
Link: https://lore.kernel.org/lkml/20250310112206.4168-1-spasswolf@web.de/

 [2]

Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kees Cook <kees@kernel.org>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Bert Karwatzki <spasswolf@web.de>
Cc: Christoph Hellwig <hch@infradead.org>

Signed-off-by: default avatarBalbir Singh <balbirs@nvidia.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarMarek Szyprowski <m.szyprowski@samsung.com>
Link: https://lore.kernel.org/r/20250414113752.3298276-1-balbirs@nvidia.com
parent d7b98ae5

kernel/dma/mapping.c

+10 −1
Original line number Diff line number Diff line
@@ -918,7 +918,7 @@ EXPORT_SYMBOL(dma_set_coherent_mask); 
 * the system, else %false.  Lack of addressing bits is the prime reason for

 * bounce buffering, but might not be the only one.

 */

bool dma_addressing_limited(struct device *dev)

static bool __dma_addressing_limited(struct device *dev)

{

	const struct dma_map_ops *ops = get_dma_ops(dev);
@@ -930,6 +930,15 @@ bool dma_addressing_limited(struct device *dev) 
		return false;

	return !dma_direct_all_ram_mapped(dev);

}



bool dma_addressing_limited(struct device *dev)

{

	if (!__dma_addressing_limited(dev))

		return false;



	dev_dbg(dev, "device is DMA addressing limited\n");

	return true;

}

EXPORT_SYMBOL_GPL(dma_addressing_limited);



size_t dma_max_mapping_size(struct device *dev)