Re: [PATCH] arm64: dts: juno: Fix DMA address translations by adding SOC bus node

[Sudeep Holla <sudeep.holla@arm.com>]

On Thu, Nov 28, 2019 at 11:50:54AM +0000, Robin Murphy wrote:
> Hi Sudeep,
> 
> On 2019-11-26 4:53 pm, Sudeep Holla wrote:
> > Commit 951d48855d86 ("of: Make of_dma_get_range() work on bus nodes")
> > reworked the logic such that of_dma_get_range() works correctly
> > starting from a bus node containing "dma-ranges".
> > 
> > Since on Juno we don't have a SoC level bus node and "dma-ranges" is
> > present only in the root node, we get the following error:
> > 
> > OF: translation of DMA address(0) to CPU address failed node(/sram@2e000000)
> > OF: translation of DMA address(0) to CPU address failed node(/uart@7ff80000)
> > ...
> > OF: translation of DMA address(0) to CPU address failed node(/mhu@2b1f0000)
> > OF: translation of DMA address(0) to CPU address failed node(/iommu@2b600000)
> > OF: translation of DMA address(0) to CPU address failed node(/iommu@2b600000)
> > OF: translation of DMA address(0) to CPU address failed node(/iommu@2b600000)
> > 
> > Let's fix it by adding a SoC bus node and moving all the devices along
> > with the "dma-ranges" inside it.
> > 
> > Cc: Rob Herring <robh+dt@kernel.org>
> > Cc: Liviu Dudau <liviu.dudau@arm.com>
> > Cc: Robin Murphy <robin.murphy@arm.com>
> > Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> > Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> > ---
> >   arch/arm64/boot/dts/arm/juno-base.dtsi        | 162 +++++++++---------
> >   arch/arm64/boot/dts/arm/juno-clocks.dtsi      |   2 +
> >   arch/arm64/boot/dts/arm/juno-cs-r1r2.dtsi     |   2 +
> >   arch/arm64/boot/dts/arm/juno-motherboard.dtsi |   2 +
> >   4 files changed, 88 insertions(+), 80 deletions(-)
> > 
> > Hi Rob, Robin,
> > 
> > Let me know if this is correct fix for the issue I am seeing with linux-next
> > on Juno. This patch is generated with -b for ease of review. With lots of
> > indentation, actual delta is:
> > 
> > 4 files changed, 1274 insertions(+), 1266 deletions(-)
> 
> Other than a few nits - the GIC should probably be under the soc node as
> it's an MMIO device, while the clocks shouldn't; the dtsi's could probably
> avoid churn with a "&soc {...}" phandle - I think this is a reasonable thing
> to do, as it's generally the preferred structure.
>

I agree and am still in confusion as what to put inside soc or not.

> The cruder but far simpler alternative would be to just drop the dma-ranges
> property - I'm not sure the effort to make all 64-bit platforms describe
> their dma-ranges has really panned out, and it isn't actually necessary for
> Juno (which is why it didn't seem like sufficient reason to do all this
> restructuring at the time, and instead I took a very liberal interpretation
> of the spec to sneak it into the root node).
>

I think I prefer that for v5.5 as a fix as this is much bigger churn. We
can do that for v5.6 if required. Let me know if you disagree. I can simply
revert your original patch adding dma-ranges for now and we can add it
later with all the soc structure.

--
Regards,
Sudeep