Re: [PATCH v2] of: Fix "dma-ranges" handling for bus controllers

From: Robin Murphy
Date: Tue Oct 04 2022 - 07:11:00 EST

On 2022-09-30 20:39, Rob Herring wrote:
On Thu, 29 Sep 2022 13:48:38 +0100, Robin Murphy wrote:
Commit 951d48855d86 ("of: Make of_dma_get_range() work on bus nodes")
relaxed the handling of "dma-ranges" for any leaf node on the assumption
that it would still represent a usage error for the property to be
present on a non-bus leaf node. However there turns out to be a fiddly
case where a bus also represents a DMA-capable device in its own right,
such as a PCIe root complex with an integrated DMA engine on its
platform side. In such cases, "dma-ranges" translation is entirely valid
for devices discovered behind the bus, but should not be erroneously
applied to the bus controller device itself which operates in its
parent's address space. Fix this by restoring the previous behaviour for
the specific case where a device is configured via its own OF node,
since it is logical to assume that a device should never represent its
own parent bus.

Reported-by: Serge Semin <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Robin Murphy <robin.murphy@xxxxxxx>

v2: Fix !HAS_DMA build error

drivers/of/address.c | 4 +++-
drivers/of/device.c | 9 ++++++++-
drivers/of/of_private.h | 5 +++++
3 files changed, 16 insertions(+), 2 deletions(-)

Applied, thanks!

I assume this was not tagged with Fixes or stable because there is not
yet a user that needs it? I didn't add it either because I'm a bit
worried about regressions and applying this just before the merge
window. So send it to stable later if anyone cares.

Indeed this was only brought to light by a patch series that Serge is working on, so although it's technically a fix I don't believe it's affecting any in-tree users yet, thus doesn't warrant backporting.