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

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Date:	Thu, 6 Nov 2014 10:11:00 +0100
From:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:	Alexandre Courbot <acourbot@...dia.com>
Cc:	"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 6 November 2014 07:37, 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?

Well, it's not that different from using the register address. I think
it helps with readability more than an arbitrary index.

>> +
>> +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 {
>>                 compatible = "nvidia,tegra124-car";
>> -               reg = <0x60006000 0x1000>;
>> +               reg = <0x0 0x60006000 0x0 0x1000>;
>>                 #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";
>> +                       };
>> +                       timing@...00000 {
>> +                               clock-frequency = <20400000>;
>> +                               nvidia,parent-clock-frequency =
>> <408000000>;
>> +                               clocks = <&tegra_car TEGRA124_CLK_PLL_P>;
>> +                               clock-names = "emc-parent";
>> +                       };
>> +               };
>> +       };
>
>
> At first it seems confusing to see a top-level node without a compatible
> property, until you realize it has already been defined before.
>
> In patch 05, you put "Example board file:" above a similar node, which is
> enough to lift that ambiguity - could you do the same here?

Oh, actually it was already in the file. I took this idea from here
for patch 05.

Thanks,

Tomeu

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