Re: [PATCH v3 04/13] of: document new emc-timings subnode in nvidia,tegra124-car

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On 11/07/2014 12:12 AM, Rob Herring wrote:
On Thu, Nov 6, 2014 at 12:37 AM, Alexandre Courbot <acourbot@xxxxxxxxxx> wrote:
On 10/30/2014 01:22 AM, Tomeu Vizoso wrote:

The EMC clock needs some extra information for changing its rate.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@xxxxxxxxxxxxx>
---
   .../bindings/clock/nvidia,tegra124-car.txt         | 46
+++++++++++++++++++++-
   1 file changed, 44 insertions(+), 2 deletions(-)

diff --git
a/Documentation/devicetree/bindings/clock/nvidia,tegra124-car.txt
b/Documentation/devicetree/bindings/clock/nvidia,tegra124-car.txt
index ded5d62..42e0588 100644
--- a/Documentation/devicetree/bindings/clock/nvidia,tegra124-car.txt
+++ b/Documentation/devicetree/bindings/clock/nvidia,tegra124-car.txt
@@ -19,12 +19,35 @@ Required properties :
     In clock consumers, this cell represents the bit number in the CAR's
     array of CLK_RST_CONTROLLER_RST_DEVICES_* registers.

+The node should contain a "emc-timings" subnode for each supported RAM
type (see
+field RAM_CODE in register PMC_STRAPPING_OPT_A), with its unit address
being its
+RAM_CODE.
+
+Required properties for "emc-timings" nodes :
+- nvidia,ram-code : Should contain the value of RAM_CODE this timing set
+  is used for.
+
+Each "emc-timings" node should contain a "timing" subnode for every
supported
+EMC clock rate. The "timing" subnodes should have the clock rate in Hz as
their
+unit address.


This seems to be a quite liberal use of unit addresses (same in the next
patch) - is this allowed by DT?

No, unit address should match a reg property.

Mmm, would you have any suggestion as to how this can be fixed? Right now what I can think of is either to replace the "clock-frequency" property by "reg" (which would be confusing), or to use a different naming scheme, e.g. timing-12750000. IIUC the naming is not essential for properly parsing these nodes, so maybe the second solution is the way to go?


+
+Required properties for "timing" nodes :
+- clock-frequency : Should contain the memory clock rate to which this
timing
+relates.
+- nvidia,parent-clock-frequency : Should contain the rate at which the
current
+parent of the EMC clock should be running at this timing.
+- clocks : Must contain an entry for each entry in clock-names.
+  See ../clocks/clock-bindings.txt for details.
+- clock-names : Must include the following entries:
+  - emc-parent : the clock that should be the parent of the EMC clock at
this
+timing.
+
   Example SoC include file:

   / {
-       tegra_car: clock {
+       tegra_car: clock@0,60006000 {

The comma here is wrong. Commas should be used when you have something
like PCI bus:dev:func for addressing.

                 compatible = "nvidia,tegra124-car";
-               reg = <0x60006000 0x1000>;
+               reg = <0x0 0x60006000 0x0 0x1000>;

The number of cell's is really irrelevant to the example.

                 #clock-cells = <1>;
                 #reset-cells = <1>;
         };
@@ -60,4 +83,23 @@ Example board file:
         &tegra_car {
                 clocks = <&clk_32k> <&osc>;
         };
+
+       clock@0,60006000 {
+               emc-timings@3 {
+                       nvidia,ram-code = <3>;
+
+                       timing@12750000 {
+                               clock-frequency = <12750000>;
+                               nvidia,parent-clock-frequency =
<408000000>;
+                               clocks = <&tegra_car TEGRA124_CLK_PLL_P>;
+                               clock-names = "emc-parent";

Why do you need both clocks and hardcoded values? clock-frequency is
the desired freq you want to set TEGRA124_CLK_PLL_P to?

That would be nvidia,parent-clock-frequency IIUC, while clock-frequency is the resulting EMC clock.


The clocks property really belongs as part of the memory controller
node or a memory device node.

I would tend to agree here. Tomeu, does it make sense to move these properties to the EMC driver instead?
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