On Thursday 18 December 2014 17:07:04 Murali Karicheri wrote:
> Add of_pci_dma_configure() to allow updating the dma configuration
> of the pci device using the configuration from the parent of
> the root bridge device.
>
> Signed-off-by: Murali Karicheri <m-karicheri2@xxxxxx>
Much better!
There is one detail that we should get right from the start here,
which is currently wrong in the platform device code, but I have so
far not dared change it:
> + /*
> + * Set default dma-mask to 32 bit. Drivers are expected to setup
> + * the correct supported dma_mask.
> + */
> + dev->coherent_dma_mask = DMA_BIT_MASK(32);
The 32-bit mask is indeed correct as the default for almost all cases,
and we must not set it larger than DMA_BIT_MASK(32). There is one
corner case though, which happens on some shmobile machines that have
a 31-bit mask on the PCI host, and I think we should use that as the
default.
> + /*
> + * Set it to coherent_dma_mask by default if the architecture
> + * code has not set it.
> + */
> + if (!dev->dma_mask)
> + dev->dma_mask = &dev->coherent_dma_mask;
> +
> + ret = of_dma_get_range(parent_np, &dma_addr, &paddr, &size);
> + if (ret < 0) {
> + dma_addr = offset = 0;
> + size = dev->coherent_dma_mask;
Can you check one thing here? I believe the size argument as returned
from of_dma_get_range is inclusive (e.g. 0x100000000), while the coherent
mask by definition is exlusive (e.g. 0xffffffff), so the size needs to
be adapted here. I haven't checked all the code here though, so I may
be wrong.
> + } else {
> + offset = PFN_DOWN(paddr - dma_addr);
> + dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", dev->dma_pfn_offset);
> + }
> + dev->dma_pfn_offset = offset;
> +
> + coherent = of_dma_is_coherent(parent_np);
> + dev_dbg(dev, "device is%sdma coherent\n",
> + coherent ? " " : " not ");
> +
> + arch_setup_dma_ops(dev, dma_addr, size, NULL, coherent);
Basically, I would use limit the size argument we pass into
arch_setup_dma_ops to the minimum of 'size' and 'dma_mask' here,
after converting into the same format. We should make sure we do the
same thing for platform_device as well, so it might be better to do
it inside of arch_setup_dma_ops instead.
Arnd
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