linux-kernel - Re: [PATCH v6 2/7] reset: mchp: sparx5: Use the second reg item when cpu-syscon is not present

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Message-Id: <d244471d-b85e-49e8-8359-60356024ce8a@app.fastmail.com>
Date: Mon, 30 Sep 2024 13:57:01 +0000
From: "Arnd Bergmann" <arnd@...db.de>
To: "Herve Codina" <herve.codina@...tlin.com>,
 "Geert Uytterhoeven" <geert@...ux-m68k.org>,
 "Andy Shevchenko" <andy.shevchenko@...il.com>,
 "Simon Horman" <horms@...nel.org>, "Lee Jones" <lee@...nel.org>,
 "derek.kiernan@....com" <derek.kiernan@....com>,
 "dragan.cvetic@....com" <dragan.cvetic@....com>,
 "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
 "Bjorn Helgaas" <bhelgaas@...gle.com>,
 "Philipp Zabel" <p.zabel@...gutronix.de>,
 "Lars Povlsen" <lars.povlsen@...rochip.com>,
 "Steen Hegelund" <Steen.Hegelund@...rochip.com>,
 "Daniel Machon" <daniel.machon@...rochip.com>, UNGLinuxDriver@...rochip.com,
 "Rob Herring" <robh@...nel.org>, "Krzysztof Kozlowski" <krzk+dt@...nel.org>,
 "Conor Dooley" <conor+dt@...nel.org>,
 "Saravana Kannan" <saravanak@...gle.com>
Cc: "David S . Miller" <davem@...emloft.net>,
 "Eric Dumazet" <edumazet@...gle.com>, "Jakub Kicinski" <kuba@...nel.org>,
 "Paolo Abeni" <pabeni@...hat.com>,
 "Horatiu Vultur" <horatiu.vultur@...rochip.com>,
 "Andrew Lunn" <andrew@...n.ch>, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, Netdev <netdev@...r.kernel.org>,
 linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 "Allan Nielsen" <allan.nielsen@...rochip.com>,
 "Luca Ceresoli" <luca.ceresoli@...tlin.com>,
 "Thomas Petazzoni" <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v6 2/7] reset: mchp: sparx5: Use the second reg item when
 cpu-syscon is not present

On Mon, Sep 30, 2024, at 12:15, Herve Codina wrote:
> In the LAN966x PCI device use case, syscon cannot be used as syscon
> devices do not support removal [1]. A syscon device is a core "system"
> device and not a device available in some addon boards and so, it is not
> supposed to be removed.
>
> In order to remove the syscon usage, use a local mapping of a reg
> address range when cpu-syscon is not present.
>
> Link: https://lore.kernel.org/all/20240923100741.11277439@bootlin.com/ [1]
> Signed-off-by: Herve Codina <herve.codina@...tlin.com>
> ---

>>  	err = mchp_sparx5_map_syscon(pdev, "cpu-syscon", &ctx->cpu_ctrl);
> -	if (err)
> +	switch (err) {
> +	case 0:
> +		break;
> +	case -ENODEV:

I was expecting a patch that would read the phandle and map the
syscon node to keep the behavior unchanged, but I guess this one
works as well.

The downside of your approach is that it requires an different
DT binding, which only works as long as there are no other
users of the syscon registers.

     Arnd