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SubjectRe: [PATCH V7 1/2] arm64: dtsi: Fix SDMMC address range
On Wed, Jan 02, 2019 at 11:36:47AM -0800, Sowjanya Komatineni wrote:
> This patch fixes the SDMMC Controllers address space to be exact
> defined register address range as per the design.
>
> SDMMC Controller supporting Command Queue has CQHCI registers at
> offset 0xF000.
>
> This fix helps to identify the Tegra SDMMC Controllers supporting
> Command Queue based on the size of address space.
>
> Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
> ---
> arch/arm64/boot/dts/nvidia/tegra186.dtsi | 6 +++---
> arch/arm64/boot/dts/nvidia/tegra194.dtsi | 4 ++--
> 2 files changed, 5 insertions(+), 5 deletions(-)

After applying these patches I'm having second thoughts about the DT
aspect of this. I know you and Timo had originally argued to advertise
the capability via an extra property in DT instead of updating the reg
property. In retrospect, I think that's the right thing to do, after
all.

The problem I'm running into is that if I apply patch 2/2 without the
first patch, then both Jetson TX2 and Jetson AGX Xavier crash on boot
because they try to access these registers (the I/O memory size is
0x10000 for all controllers). So we're effectively breaking ABI with
existing device trees.

I don't know of a way to work around that other than the separate
property. Would you mind changing the series to contain:

1) a patch updating the device tree bindings with the new
optional property that would mark SDMMC4 as CQE capable
(make sure to Cc devicetree@vger.kernel.org on that patch)

2) replace this patch by one which only adds the new
"supports-cqe" property

3) update the second patch to make the decision based on the
flag rather than the I/O memory size

Sorry for the back and forth on this. I evidently hadn't thought this
through.

Thierry
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