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
Documentation/DMA-API.txt has moved to Documentation/core-api/dma-api.rst
Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
Message-ID: <20231101070201.4066998-1-lizhijian@fujitsu.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
All architecture-independent users of virt_to_bus() and bus_to_virt()
have been fixed to use the dma mapping interfaces or have been
removed now. This means the definitions on most architectures, and the
CONFIG_VIRT_TO_BUS symbol are now obsolete and can be removed.
The only exceptions to this are a few network and scsi drivers for m68k
Amiga and VME machines and ppc32 Macintosh. These drivers work correctly
with the old interfaces and are probably not worth changing.
On alpha and parisc, virt_to_bus() were still used in asm/floppy.h.
alpha can use isa_virt_to_bus() like x86 does, and parisc can just
open-code the virt_to_phys() here, as this is architecture specific
code.
I tried updating the bus-virt-phys-mapping.rst documentation, which
started as an email from Linus to explain some details of the Linux-2.0
driver interfaces. The bits about virt_to_bus() were declared obsolete
backin 2000, and the rest is not all that relevant any more, so in the
end I just decided to remove the file completely.
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Acked-by: Helge Deller <deller@gmx.de> # parisc
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Frank Li