On 10/07/2015 09:26 AM, Jon Hunter wrote:
On 06/10/15 23:57, Stephen Warren wrote:
On 10/06/2015 03:16 AM, Jon Hunter wrote:
On 05/10/15 14:12, Mark Rutland wrote:
On Mon, Oct 05, 2015 at 01:10:06PM +0100, Jon Hunter wrote:
Add device-tree binding documentation for the Tegra210 Audio DMA
controller.
Signed-off-by: Jon Hunter <jonathanh@xxxxxxxxxx>
---
.../devicetree/bindings/dma/tegra210-adma.txt | 63
++++++++++++++++++++++
1 file changed, 63 insertions(+)
create mode 100644
Documentation/devicetree/bindings/dma/tegra210-adma.txt
diff --git a/Documentation/devicetree/bindings/dma/tegra210-adma.txt
b/Documentation/devicetree/bindings/dma/tegra210-adma.txt
new file mode 100644
index 000000000000..df0e46868a63
--- /dev/null
+++ b/Documentation/devicetree/bindings/dma/tegra210-adma.txt
@@ -0,0 +1,63 @@
+* NVIDIA Tegra Audio DMA (ADMA) controller
+
+Required properties:
+- compatible: Must be "nvidia,tegra210-adma".
+- reg: Should contain DMA registers location and length. This
should be
+ a single entry that includes all of the per-channel registers in one
+ contiguous bank.
+- interrupt-parent: Phandle to the interrupt parent controller.
+- interrupts: Should contain all of the per-channel DMA interrupts in
+ ascending order with respect to the DMA channel index.
+- clocks: Must contain one entry for the ADMA module clock,
"adma_ape".
+- clock-names: Must contain the entry "adma_ape".
+- dma-channels: Must be 22. Defines the number of DMA channels
supported
+ by the DMA controller.
If this has to be a fixed value, why is it necessary? Why does the
driver not just know this?
Are there other instances of this IP block where this differs?
So this will change for future devices and yes it may seem silly now to
have something that fixed and appears to be constant but I was trying to
future proof the binding. May be the comment should read "For tegra210
must be 22", however, I thought the compatible string would imply this.
Typically you'd want a table in the driver that maps from compatible
value to the set of per-SoC data that's associated with the compatible
value. Then, you don't need to put this data into the DT.
Yes I have seen that which I was not sure that I was a fan of, given
that we have DT and its purpose is to describe the hardware. So may be
the problem I have is deciding on which hardware parameters should be
described in DT versus those that should be place in the driver itself.
I am not sure if there is a rule of thumb for this type of thing?
It seems to be a matter of preference.
I think DT is mainly about identifying which HW is present. Facets of
the HW that are fixed (100% derivable from the compatible value) belong
in the driver. If we took the opposite view, we should put a description
of every register/field layout in the DT in case they change on new HW
and we don't want to edit the driver code to take account of that, and
in fact should put byte code into the DT since simple data might not be
enough to allow us not to edit the driver. Facets that vary between
boards, use-cases, etc. are the main benefit of DT in my opinion, not
slow-moving data specific to SoCs.
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