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SubjectRe: [PATCH v3 04/13] of: document new emc-timings subnode in nvidia,tegra124-car
On 11/07/2014 12:12 AM, Rob Herring wrote:
> On Thu, Nov 6, 2014 at 12:37 AM, Alexandre Courbot <acourbot@nvidia.com> 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@collabora.com>
>>> ---
>>> .../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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