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f7ae20f2fc
There are bunch of codes in driver like
if (dma_set_mask_and_coherent(dev, DMA_BIT_MASK(64)))
dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32))
Actually it is wrong because if dma_set_mask_and_coherent(64) fails,
dma_set_mask_and_coherent(32) will fail for the same reason.
And dma_set_mask_and_coherent(64) never returns failure.
According to the definition of dma_set_mask(), it indicates the width of
address that device DMA can access. If it can access 64-bit address, it
must access 32-bit address inherently. So only need set biggest address
width.
See below code fragment:
dma_set_mask(mask)
{
mask = (dma_addr_t)mask;
if (!dev->dma_mask || !dma_supported(dev, mask))
return -EIO;
arch_dma_set_mask(dev, mask);
*dev->dma_mask = mask;
return 0;
}
dma_supported() will call dma_direct_supported or iommux's dma_supported
call back function.
int dma_direct_supported(struct device *dev, u64 mask)
{
u64 min_mask = (max_pfn - 1) << PAGE_SHIFT;
/*
* Because 32-bit DMA masks are so common we expect every architecture
* to be able to satisfy them - either by not supporting more physical
* memory, or by providing a ZONE_DMA32. If neither is the case, the
* architecture needs to use an IOMMU instead of the direct mapping.
*/
if (mask >= DMA_BIT_MASK(32))
return 1;
...
}
The iommux's dma_supported() actually means iommu requires devices's
minimized dma capability.
An example:
static int sba_dma_supported( struct device *dev, u64 mask)()
{
...
* check if mask is >= than the current max IO Virt Address
* The max IO Virt address will *always* < 30 bits.
*/
return((int)(mask >= (ioc->ibase - 1 +
(ioc->pdir_size / sizeof(u64) * IOVP_SIZE) )));
...
}
1 means supported. 0 means unsupported.
Correct document to make it more clear and provide correct sample code.
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
[jc: fixed then/than typo]
Link: https://lore.kernel.org/r/20240401174159.642998-1-Frank.Li@nxp.com
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| .. | ||
| irq | ||
| wrappers | ||
| asm-annotations.rst | ||
| assoc_array.rst | ||
| boot-time-mm.rst | ||
| cachetlb.rst | ||
| circular-buffers.rst | ||
| cpu_hotplug.rst | ||
| debug-objects.rst | ||
| debugging-via-ohci1394.rst | ||
| dma-api-howto.rst | ||
| dma-api.rst | ||
| dma-attributes.rst | ||
| dma-isa-lpc.rst | ||
| entry.rst | ||
| errseq.rst | ||
| genalloc.rst | ||
| generic-radix-tree.rst | ||
| genericirq.rst | ||
| gfp_mask-from-fs-io.rst | ||
| idr.rst | ||
| index.rst | ||
| kernel-api.rst | ||
| kobject.rst | ||
| kref.rst | ||
| librs.rst | ||
| local_ops.rst | ||
| maple_tree.rst | ||
| memory-allocation.rst | ||
| memory-hotplug.rst | ||
| mm-api.rst | ||
| netlink.rst | ||
| packing.rst | ||
| padata.rst | ||
| pin_user_pages.rst | ||
| printk-basics.rst | ||
| printk-formats.rst | ||
| printk-index.rst | ||
| protection-keys.rst | ||
| rbtree.rst | ||
| refcount-vs-atomic.rst | ||
| symbol-namespaces.rst | ||
| this_cpu_ops.rst | ||
| timekeeping.rst | ||
| tracepoint.rst | ||
| unaligned-memory-access.rst | ||
| watch_queue.rst | ||
| workqueue.rst | ||
| xarray.rst | ||