On Mon, Dec 05, 2016 at 12:26:19PM +0000, Lorenzo Pieralisi wrote:

The introduction of acpi_dma_configure() allows to configure DMA
and related IOMMU for any device that is DMA capable. To achieve
that goal it ensures DMA masks are set-up to sane default values
before proceeding with IOMMU and DMA ops configuration.

On x86/ia64 systems, through acpi_bind_one(), acpi_dma_configure() is
called for every device that has an ACPI companion, in that every device
is considered DMA capable on x86/ia64 systems (ie acpi_get_dma_attr() API),
which has the side effect of initializing dma masks also for
pseudo-devices (eg CPUs and memory nodes) and potentially for devices
whose dma masks were not set-up before the acpi_dma_configure() API was
introduced, which may have noxious side effects.

Therefore, in preparation for IORT firmware specific DMA masks set-up,
wrap the default DMA masks set-up in acpi_dma_configure() inside an IORT
specific wrapper that reverts to a NOP on x86/ia64 systems, restoring the
default expected behaviour on x86/ia64 systems and keeping DMA default
masks set-up on IORT based (ie ARM) arch configurations.

Signed-off-by: Lorenzo Pieralisi <redacted>
Cc: Will Deacon <redacted>
Cc: Hanjun Guo <redacted>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Tomasz Nowicki <redacted>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: "Rafael J. Wysocki" <redacted>
Cc: Sricharan R <redacted>
---
Joerg,

pending Rafael's ACK on it, given the 4.10 release timing and that the
series is queued via the IOMMU tree please consider applying this patch to
your arm/smmu branch for 4.10, it is not fixing a bug but it is modifying
the x86/ia64 code path; I prefer preventing any issue related to default
dma masks on x86/ia64 so I hope it can get merged along with the rest of
the ACPI IORT SMMU series.

Thanks a lot and apologies,
Lorenzo

 drivers/acpi/arm64/iort.c | 22 ++++++++++++++++++++++
 drivers/acpi/scan.c       | 14 +-------------
 include/linux/acpi_iort.h |  2 ++
 3 files changed, 25 insertions(+), 13 deletions(-)

Looks straightforward to me:

Acked-by: Will Deacon <redacted>

Joerg can probably just pick this on top of his queue.

Will