linux-kernel - Re: [PATCH] firmware: smccc: default ARM_SMCCC_SOC

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Message-ID: <ax35tcjafo2qvvjpg2al5o6gz7khbwmtp2jrh5xemiwjq6rpo7@64cown27pueg>
Date: Thu, 15 Jan 2026 22:40:15 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Satya Durga Srinivasu Prabhala <satya.prabhala@....qualcomm.com>
Cc: Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Sudeep Holla <sudeep.holla@....com>, linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        trilok.soni@....qualcomm.com
Subject: Re: [PATCH] firmware: smccc: default ARM_SMCCC_SOC_ID to disabled

On Thu, Jan 15, 2026 at 12:14:15PM -0800, Satya Durga Srinivasu Prabhala wrote:
> 
> On 1/14/2026 11:37 AM, Dmitry Baryshkov wrote:
> > On Wed, Jan 14, 2026 at 10:04:21AM -0800, Satya Durga Srinivasu Prabhala wrote:
> > > Hello Dmitry,
> > > 
> > > On 1/13/2026 3:25 AM, Dmitry Baryshkov wrote:
> > > > On Mon, Jan 12, 2026 at 10:24:06PM -0800, Satya Durga Srinivasu Prabhala wrote:
> > > > > The ARM SMCCC SoC ID driver is currently enabled by default and publishes
> > > > > SMCCC-provided SoC identification into /sys/bus/soc/devices/socX/*.
> > > > > 
> > > > > On platforms where a vendor SoC driver already exposes widely-consumed
> > > > > attributes (e.g. Qualcomm socinfo [1]), enabling the SMCCC driver changes
> > > > > the format of /sys/devices/soc0/soc_id (e.g. "jep106:XXYY:ZZZZ" instead
> > > > > of a vendor logical ID like "519") and breaks existing userspace consumers.
> > > > > 
> > > > > Flip the default of CONFIG_ARM_SMCCC_SOC_ID from y to n. Platforms that
> > > > > prefer SMCCC over a vendor driver can explicitly enable it.
> > > > NAK, the userspace should not depend on the exact kernel configuration.
> > > > Consider working with distribution kernels, which would enable this
> > > > driver anyway.
> > > As I mentioned in the other replies, vendor interface exists before the
> > > standard
> > > interface and user space heavily relies on soc0 already. If not disabling
> > > the
> > > SMCCC SOC ID by default. I believe, we should  at-least have a way to make
> > > sure vendors can disable SMCCC SOC ID by some means or have vendor
> > > interface takes precedence.
> > Please correct me if I'm wrong, what do you observe? SMCCC device on
> > soc0 and qcom_socinfo at soc1?
> 
> Yes, that is absolutely correct, Dmitry.
> 
> > In such a case the ABI file, Documentation/ABI/testing/sysfs-devices-soc clearly
> > defines that there might be several different SoC devices (identified by
> > different drivers, etc). If the userspace depends on qcom_socinfo device
> > being soc0, then the userspace is broken.
> 
> 
> Yes, there is no question about that. User space had certain assumption on
> SoC Devices. The point to note is, user space had those assumptions based on
> vendor interfaces which existed from long time.

As I wrote in another email, you are correct here. But not precise.
Userspace had certain assumptions regarding vendor _firmware_.

The whole situation is different from e.g. somebody deciding to add
soc_device_register() call to the BT/WiFi SoC driver. In the latter case
it would be a kernel regressing the userspace (which is generally
disallowed). In you case it's Qualcomm firmware regressing
Qualcomm-specific Android userspace.

> > Last, but not least, the soc_id format is documented in the ABI
> > document. It is clearly allowed to have jep106 format in the soc_id. So,
> > I think, you have two options: disable SMCCC 1.2+ in the firmware or
> > adapt the userspace. You can't control e.g. the kernel that will be
> > running on your platform (it very well can be a standard distro kernel
> > from Debian, Ubuntu or Fedora, which obviously will have that driver
> > enabled).
> 
> 
> IMHO, vendors at-least should have a way to choose what interface needs to
> be
> exposed to user space (vendor vs SMCCC).

But you already have. Kconfig options, etc. What you can do is turn
ARM_SMCCC_SOC_ID into a module (I'm not sure if SMCCC maintainers would
agree to that, but at least it is something which makes sense to me).

> > > Best,
> > > Satya
> > > > > This avoids unexpected format changes and keeps the generic SoC sysfs
> > > > > stable on systems that rely on vendor-specific identification.
> > > > > 
> > > > > [1]
> > > > > Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/soc/qcom/socinfo.c
> > > > > 
> > > > > Signed-off-by: Satya Durga Srinivasu Prabhala <satya.prabhala@....qualcomm.com>
> > > > > ---
> > > > >    drivers/firmware/smccc/Kconfig | 5 ++++-
> > > > >    1 file changed, 4 insertions(+), 1 deletion(-)
> > > > > 

-- 
With best wishes
Dmitry