linux-kernel - Re: [PATCH 2/2] soc: nxp: Add a simple NXP LPC32xx socinfo driver

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Message-ID: <1a336af6-6c27-4211-9c8c-ede4d091eb17@mleia.com>
Date: Fri, 2 Jan 2026 15:21:44 +0200
From: Vladimir Zapolskiy <vz@...ia.com>
To: Krzysztof Kozlowski <krzk@...nel.org>, Arnd Bergmann <arnd@...db.de>
Cc: Piotr Wojtaszczyk <piotr.wojtaszczyk@...esys.com>,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] soc: nxp: Add a simple NXP LPC32xx socinfo driver

On 1/2/26 14:54, Krzysztof Kozlowski wrote:
> On 02/01/2026 13:36, Vladimir Zapolskiy wrote:
>> On 1/2/26 11:58, Krzysztof Kozlowski wrote:
>>> On 02/01/2026 00:56, Vladimir Zapolskiy wrote:
>>>> Add NXP LPC32xx specific driver to get unique SoC ID from System Control
>>>> Block registers and export it to userspace.
>>>>
>>>> Signed-off-by: Vladimir Zapolskiy <vz@...ia.com>
>>>> ---
>>>>    drivers/soc/Kconfig           |   1 +
>>>>    drivers/soc/Makefile          |   1 +
>>>>    drivers/soc/nxp/Kconfig       |  16 +++++
>>>>    drivers/soc/nxp/Makefile      |   2 +
>>>>    drivers/soc/nxp/lpc32xx-soc.c | 114 ++++++++++++++++++++++++++++++++++
>>>>    5 files changed, 134 insertions(+)
>>>>    create mode 100644 drivers/soc/nxp/Kconfig
>>>>    create mode 100644 drivers/soc/nxp/Makefile
>>>>    create mode 100644 drivers/soc/nxp/lpc32xx-soc.c
>>>>
>>>> diff --git a/drivers/soc/Kconfig b/drivers/soc/Kconfig
>>>> index a2d65adffb80..c21b0d2f58fc 100644
>>>> --- a/drivers/soc/Kconfig
>>>> +++ b/drivers/soc/Kconfig
>>>> @@ -18,6 +18,7 @@ source "drivers/soc/loongson/Kconfig"
>>>>    source "drivers/soc/mediatek/Kconfig"
>>>>    source "drivers/soc/microchip/Kconfig"
>>>>    source "drivers/soc/nuvoton/Kconfig"
>>>> +source "drivers/soc/nxp/Kconfig"
>>>>    source "drivers/soc/pxa/Kconfig"
>>>>    source "drivers/soc/qcom/Kconfig"
>>>>    source "drivers/soc/renesas/Kconfig"
>>>> diff --git a/drivers/soc/Makefile b/drivers/soc/Makefile
>>>> index 47a3925ff84c..a04c21a8a5a4 100644
>>>> --- a/drivers/soc/Makefile
>>>> +++ b/drivers/soc/Makefile
>>>> @@ -24,6 +24,7 @@ obj-y				+= loongson/
>>>>    obj-y				+= mediatek/
>>>>    obj-y				+= microchip/
>>>>    obj-y				+= nuvoton/
>>>> +obj-y				+= nxp/
>>>>    obj-y				+= pxa/
>>>>    obj-y				+= qcom/
>>>>    obj-y				+= renesas/
>>>
>>> Missing maintainers entry.
>>>
>>>
>>>> +
>>>> +static int lpc32xx_soc_probe(struct platform_device *pdev)
>>>> +{
>>>> +	struct soc_device_attribute *soc_dev_attr;
>>>> +	struct device *dev = &pdev->dev;
>>>> +	struct soc_device *soc_dev;
>>>> +	struct regmap *scb;
>>>> +	u32 serial_id[4];
>>>> +	int ret;
>>>> +
>>>> +	soc_dev_attr = devm_kzalloc(dev, sizeof(*soc_dev_attr), GFP_KERNEL);
>>>> +	if (!soc_dev_attr)
>>>> +		return -ENOMEM;
>>>> +
>>>> +	soc_dev_attr->family = "NXP LPC32xx";
>>>> +
>>>> +	ret = of_property_read_string(of_root, "model", &soc_dev_attr->machine);
>>>> +	if (ret)
>>>> +		return ret;
>>>> +
>>>> +	scb = syscon_regmap_lookup_by_compatible("nxp,lpc3220-scb");
>>>
>>> This is undocumented ABI.
>>
>> What is the expected level of documentation for syscon?
> 
> git grep nxp,lpc3220-scb
> 
> gives me 0 results.
> 
> Documentation is supposed to be in this patchset. If it is not, you have
> changelog part to explain dependencies and unusual things.

The documentation is under review, as a DT maintainer you are in To: list
and should have it in the mailbox, for anyone's convenience the dependency
is mentioned in the cover letter to this changeset also.

>>
>>> Anyway, you should look up devices via phandles.
>>>
>>
>> I may miss the context, was syscon_regmap_lookup_by_compatible() deprecated?
> 
> Not deprecated. It has its own purpose, so you can explain why here you
> cannot have phandle.
> 
> Without phandle you do not have proper device probe ordering and you do
> not properly express the dependency between hardware modules. Maybe this
> is not even real hardware, which you attach your driver to, so that's
> another thing to consider. Anyway, commit msg should explain all these.

Ack.

>>
>> Most of drivers/soc uses syscon_regmap_lookup_by_compatible() variant over
>> syscon_regmap_lookup_by_phandle(), and overall
> 
> They have their own reason.

Here the reason to use syscon by a compatible is the same reason as it's
among the sibling drivers, I'll specify it in the commit message, thanks.

FWIW there is no intention to convert the SCB register region into its
owm device.

>>
>> % git grep syscon_regmap_lookup_by_compatible v6.19-rc1 | wc -l
>> 105
>>

-- 
Best wishes,
Vladimir