linux-kernel - Re: [PATCH v1 3/3] soc: aspeed: lpc-pcc: Add PCC controller support

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Message-ID: <6fd7cd57261ddf9831f57dc4c637b24e9f8982d9.camel@codeconstruct.com.au>
Date: Tue, 18 Feb 2025 11:26:53 +1030
From: Andrew Jeffery <andrew@...econstruct.com.au>
To: Krzysztof Kozlowski <krzk@...nel.org>, Kevin Chen
 <kevin_chen@...eedtech.com>, lee@...nel.org, robh@...nel.org,
 krzk+dt@...nel.org,  conor+dt@...nel.org, joel@....id.au,
 chiawei_wang@...eedtech.com,  linux-aspeed@...ts.ozlabs.org,
 linux-arm-kernel@...ts.infradead.org,  linux-kernel@...r.kernel.org
Cc: "tomer.maimon" <tomer.maimon@...oton.com>
Subject: Re: [PATCH v1 3/3] soc: aspeed: lpc-pcc: Add PCC controller support

On Mon, 2025-02-17 at 13:00 +0100, Krzysztof Kozlowski wrote:
> On 17/02/2025 12:48, Kevin Chen wrote:
> > +
> > +       pcc->mdev.parent = dev;
> > +       pcc->mdev.minor = MISC_DYNAMIC_MINOR;
> > +       pcc->mdev.name = devm_kasprintf(dev, GFP_KERNEL, "%s%d",
> > DEVICE_NAME,
> > +                                       pcc->mdev_id);
> > +       pcc->mdev.fops = &pcc_fops;
> > +       rc = misc_register(&pcc->mdev);
> > +       if (rc) {
> > +               dev_err(dev, "Couldn't register misc device\n");
> > +               goto err_free_kfifo;
> > +       }
> 
> You cannot expose user-space interfaces from SoC drivers. Use
> appropriate subsystem for this with proper ABI documentation.
> 
> See:
> https://lore.kernel.org/all/bc5118f2-8982-46ff-bc75-d0c71475e909@app.fastmail.com/
> and more discussions on LKML

Further, drivers/misc/aspeed-lpc-snoop.c already exists:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9f4f9ae81d0affc182f54dd00285ddb90e0b3ae1

Kevin: Did you consider reworking it?

Nuvoton have a similar capability in their NPCM BMC SoC(s) with the
"BPC" ("BIOS POST Code" controller). There should be some consensus on
the binding and userspace interface.

Andrew