linux-kernel - Re: [PATCH] dt-bindings: display: stm32: add pixel clock mandatory property

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Message-ID: <e7f46e2c-2cd9-bdd4-221a-109cdc9852b1@st.com>
Date:   Fri, 27 Oct 2017 14:52:21 +0000
From:   Philippe CORNU <philippe.cornu@...com>
To:     Rob Herring <robh@...nel.org>
CC:     Arnd Bergmann <arnd@...db.de>,
        Russell King <linux@...linux.org.uk>,
        "Mark Rutland" <mark.rutland@....com>,
        Archit Taneja <architt@...eaurora.org>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        David Airlie <airlied@...ux.ie>,
        "Philipp Zabel" <p.zabel@...gutronix.de>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Bhumika Goyal <bhumirks@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Yannick FERTRE <yannick.fertre@...com>,
        Vincent ABRIOU <vincent.abriou@...com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Gabriel FERNANDEZ <gabriel.fernandez@...com>,
        Ludovic BARRE <ludovic.barre@...com>,
        Fabien DESSENNE <fabien.dessenne@...com>,
        "Mickael REULIER" <mickael.reulier@...com>
Subject: Re: [PATCH] dt-bindings: display: stm32: add pixel clock mandatory
 property

Hi Rob,

On 10/27/2017 04:38 PM, Rob Herring wrote:
> On Thu, Oct 26, 2017 at 06:12:36PM +0200, Philippe Cornu wrote:
>> Add the DPI/RGB input pixel clock in mandatory properties
>> because it really offers a better preciseness for timing
>> computations.
>> Note: Fix also the DSI panel example where "ref" & "pclk"
>> clocks were swapped.
>>
>> Signed-off-by: Philippe Cornu <philippe.cornu@...com>
>> ---
>>   Documentation/devicetree/bindings/display/st,stm32-ltdc.txt | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/devicetree/bindings/display/st,stm32-ltdc.txt b/Documentation/devicetree/bindings/display/st,stm32-ltdc.txt
>> index 0292522..99823fb 100644
>> --- a/Documentation/devicetree/bindings/display/st,stm32-ltdc.txt
>> +++ b/Documentation/devicetree/bindings/display/st,stm32-ltdc.txt
>> @@ -28,6 +28,7 @@ Mandatory properties specific to STM32 DSI:
>>   - #size-cells: Should be <0>.
>>   - compatible: "st,stm32-dsi".
>>   - clock-names:
>> +  - DPI/RGB input pixel clock string name, must be "px_clk".
>>     - phy pll reference clock string name, must be "ref".
> 
> Where's pclk?

pclk is described in the generic part 
(Documentation/devicetree/bindings/display/bridge/dw_mipi_dsi.txt) as 
mandatory.

In st,stm32-ltdc.txt (specific part), I have documented that "For all 
mandatory properties & nodes, please refer to the related documentation 
in [5]".

Do you think it is clear enough?

> 
> The new clock should be last to be backwards compatible.
> 

ok.

Many thanks for your review and your support,

Philippe :-)

>>   - resets: see [5].
>>   - reset-names: see [5].
>> @@ -97,8 +98,9 @@ Example 2: DSI panel
>>   			#size-cells = <0>;
>>   			compatible = "st,stm32-dsi";
>>   			reg = <0x40016c00 0x800>;
>> -			clocks = <&rcc 1 CLK_F469_DSI>, <&clk_hse>;
>> -			clock-names = "ref", "pclk";
>> +			clocks = <&rcc 1 CLK_F469_DSI>, <&rcc 1 CLK_LCD>,
>> +				 <&clk_hse>;
>> +			clock-names = "pclk", "px_clk", "ref";
>>   			resets = <&rcc STM32F4_APB2_RESET(DSI)>;
>>   			reset-names = "apb";
>>   
>> -- 
>> 1.9.1
>>