linux-kernel - Re: [PATCH v2 0/4] Add overlays to disable optional hardware in k3-am6xx-phycore-som boards

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Message-ID: <629a95ac-3f40-412f-b983-312f434bfb2f@ti.com>
Date: Wed, 12 Jun 2024 15:49:46 +0530
From: Vignesh Raghavendra <vigneshr@...com>
To: Nathan Morrisson <nmorrisson@...tec.com>, <nm@...com>, <kristo@...nel.org>,
        <robh@...nel.org>, <krzk+dt@...nel.org>, <conor+dt@...nel.org>
CC: <linux-arm-kernel@...ts.infradead.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <upstream@...ts.phytec.de>,
        <w.egorov@...tec.de>
Subject: Re: [PATCH v2 0/4] Add overlays to disable optional hardware in
 k3-am6xx-phycore-som boards



On 05/06/24 04:45, Nathan Morrisson wrote:
> Hi Vignesh,
> 
> On 6/3/24 10:41 AM, Vignesh Raghavendra wrote:
>> Hi Nathan,
>>
>> On 29/05/24 04:21, Nathan Morrisson wrote:
>>> Add three overlays to disable the eth phy, rtc, and spi nor. These
>>> overlays will be used to disable device tree nodes for components
>>> that are optionally not populated.
>>>
>>> v2:
>>>    - Add build time tests in makefile
>>>
>>> Nathan Morrisson (4):
>>>    arm64: dts: ti: k3-am64-phycore-som: Add serial_flash label
>>
>>>    arm64: dts: ti: k3-am6xx-phycore-som: Add overlay to disable eth phy
>>>    arm64: dts: ti: k3-am6xx-phycore-som: Add overlay to disable rtc
>>>    arm64: dts: ti: k3-am6xx-phycore-som: Add overlay to disabl spi nor
>>>
>>>   arch/arm64/boot/dts/ti/Makefile               | 17 +++++++++++++++++
>>>   .../boot/dts/ti/k3-am64-phycore-som.dtsi      |  2 +-
>>>   .../ti/k3-am6xx-phycore-disable-eth-phy.dtso  | 19 +++++++++++++++++++
>>>   .../dts/ti/k3-am6xx-phycore-disable-rtc.dtso  | 15 +++++++++++++++
>>>   .../ti/k3-am6xx-phycore-disable-spi-nor.dtso  | 15 +++++++++++++++
>>>   5 files changed, 67 insertions(+), 1 deletion(-)
>>>   create mode 100644
>>> arch/arm64/boot/dts/ti/k3-am6xx-phycore-disable-eth-phy.dtso
>>>   create mode 100644
>>> arch/arm64/boot/dts/ti/k3-am6xx-phycore-disable-rtc.dtso
>>>   create mode 100644
>>> arch/arm64/boot/dts/ti/k3-am6xx-phycore-disable-spi-nor.dtso
>>>
>> I am not sure if this a common practice to have overlays to disable
>> missing components (at least I dont see such dtso in kernel). I would
>> like to see an what DT maintainers feel as such dtsos can explode in
>> numbers.
>>
>> Is this something that U-Boot can detect and fix up for the Linux DT?

> We have an EEPROM on our board with information on what is populated on     
> that particular board. We will apply these overlays based on that EEPROM
> data.

Typical usage of overlay is to keep the minimum in baseboard and enable
optional components in the overlay. But it would also depend on whats
information is present in the EEPROM.

Could you provide bit more color on whats in EEPROM and how each overlay
would be applied? Please add the same to commit message and respin.

>>
>> Unpopulated SPI flash and RTC should ideally not be an issue as drivers
>> would gracefully fail albeit with some sort of error msg.
>> Not so sure about Eth PHYs though.
>>
>> Also, Are these dtso's mutually exclusive? ie can SoM have SPI flash but
>> not RTC, have RTC and SPI Flash but no ETH PHY?
> 
> They are not mutually exclusive, you could have any combination of
> overlays applied.
> 
> 
> Regards,
> 
> Nathan
> 
>>

-- 
Regards
Vignesh