[PATCH v2] of: Restrict DMA configuration

[Rob Herring]

On Thu, Aug 31, 2017 at 5:32 AM, Robin Murphy <robin.murphy at arm.com> wrote:
> Moving DMA configuration to happen later at driver probe time had the
> unnoticed side-effect that we now perform DMA configuration for *every*
> device represented in DT, rather than only those explicitly created by
> the of_platform and PCI code.
>
> As Christoph points out, this is not really the best thing to do. Whilst
> there may well be other DMA-capable buses that can benefit from having
> their children automatically configured after the bridge has probed,
> there are also plenty of others like USB, MDIO, etc. that definitely do
> not support DMA and should not be indiscriminately processed.
>
> The good news is that in most cases the DT "dma-ranges" property serves
> as an appropriate indicator - per a strict interpretation of the spec,
> anything lacking a "dma-ranges" property should be considered not to
> have a mapping of DMA address space from its children to its parent,
> thus anything for which of_dma_get_range() does not succeed does not
> need DMA configuration. Certain bus types have a general expectation of
> DMA capability and carry a well-established precedent that an absent
> "dma-ranges" implies the same as the empty property, so we automatically
> opt those in to DMA configuration regardless, to avoid regressing most
> existing platforms.
>
> Fixes: 09515ef5ddad ("of/acpi: Configure dma operations at probe time for platform/amba/pci bus devices")
> Reported-by: Christoph Hellwig <hch at lst.de>
> Signed-off-by: Robin Murphy <robin.murphy at arm.com>
> ---
>
> v2: Updated commit message to be more reasonable
>
>  drivers/of/device.c | 48 ++++++++++++++++++++++++++++++++----------------
>  1 file changed, 32 insertions(+), 16 deletions(-)

Acked-by: Rob Herring <robh at kernel.org>