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Subject: Re: [PATCH] arm64: dts: stingray: use NUM_SATA to configure number of
 sata ports
To:     Scott Branden <scott.branden@broadcom.com>,
        Rob Herring <robh+dt@kernel.org>
Cc:     Mark Rutland <mark.rutland@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>, Ray Jui <rjui@broadcom.com>,
        BCM Kernel Feedback <bcm-kernel-feedback-list@broadcom.com>,
        devicetree@vger.kernel.org,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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From:   Florian Fainelli <f.fainelli@gmail.com>
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Date:   Wed, 13 Jun 2018 17:46:32 -0700
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On 06/13/2018 01:18 PM, Scott Branden wrote:
> Hi Rob,
> 
> Thanks for comment - reply inline.
> 
> 
> On 18-06-13 12:31 PM, Florian Fainelli wrote:
>> On 06/12/2018 03:54 PM, Rob Herring wrote:
>>> On Thu, Jun 7, 2018 at 12:53 PM, Scott Branden
>>> <scott.branden@broadcom.com> wrote:
>>>> Hi Rob,
>>>>
>>>> Could you please kindly comment on change below.
>>>>
>>>> It allows board variants to be added easily via a simple define for
>>>> different number of SATA ports.
>>>>
>>>>
>>>>
>>>> On 18-06-04 09:22 AM, Florian Fainelli wrote:
>>>>> On 05/18/2018 11:34 AM, Scott Branden wrote:
>>>>>> Move remaining sata configuration to stingray-sata.dtsi and enable
>>>>>> ports based on NUM_SATA defined.
>>>>>> Now, all that needs to be done is define NUM_SATA per board.
>>>>> Rob could you review this and let us know if this approach is okay or
>>>>> not? Thank you!
>>>>>
>>>>>> Signed-off-by: Scott Branden <scott.branden@broadcom.com>
>>>>>> ---
>>>>>> diff --git a/arch/arm64/boot/dts/broadcom/stingray/stingray-sata.dtsi
>>>>>> b/arch/arm64/boot/dts/broadcom/stingray/stingray-sata.dtsi
>>>>>> index 8c68e0c..7f6d176 100644
>>>>>> --- a/arch/arm64/boot/dts/broadcom/stingray/stingray-sata.dtsi
>>>>>> +++ b/arch/arm64/boot/dts/broadcom/stingray/stingray-sata.dtsi
>>>>>> @@ -43,7 +43,11 @@
>>>>>>                          interrupts = <GIC_SPI 321
>>>>>> IRQ_TYPE_LEVEL_HIGH>;
>>>>>>                          #address-cells = <1>;
>>>>>>                          #size-cells = <0>;
>>>>>> +#if (NUM_SATA > 0)
>>>>>> +                       status = "okay";
>>>>>> +#else
>>>>>>                          status = "disabled";
>>>>>> +#endif
>>> This only works if ports are contiguously enabled (0-N). You might not
>>> care, but it is not a pattern that works in general.
> Correct - all board designs that include this dtsi file follow such
> commonality (ie. design with SATA0 first, etc).  By having common board
> designs it allows for commonality in dts files rather than duplicating
> information everywhere.  If somebody designs a bizarro board they are
> free to create their own dts file of course.
>>>   And I'm not a fan
>>> of C preprocessing in DT files in general beyond just defines for
>>> single numbers.
> The use of a define to specify the number of SATA ports in the board
> design meets our requirements of being able to maintain many boards.  We
> need a method to specify the number of ports in the board design rather
> than copying and pasting the information in many dts files.  If you have
> an alternative upstreamable mechanism to manage the configuration of
> many boards without copy and paste that would be ideal?

We had discussed this off-list, but I really think you should be having
some sort of higher level scripting engine which is able to generate
valid per-board DTS files and not have the kernel and its use of the C
pre-processor attempt to solve your problems because a) it's the wrong
place, and b) it is limited.
--
Florian