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

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Message-ID: <545C5927.3010001@nvidia.com>
Date:	Fri, 7 Nov 2014 14:31:19 +0900
From:	Alexandre Courbot <acourbot@...dia.com>
To:	Rob Herring <robherring2@...il.com>
CC:	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	Rob Herring <robh+dt@...nel.org>,
	"Pawel Moll" <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"Stephen Warren" <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	Peter De Schrijver <pdeschrijver@...dia.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [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@...dia.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@...labora.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@...50000 {
>>> +                               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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