linux-kernel - Re: [PATCH v2 0/3] pinctrl: single: bit-per-mux DT flexibility, probe robustness, and consistent pinconf offsets

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Message-ID: <CAD++jLm2a1-G7QQBb+u68DH_RT6kc4=vpqZWQcirvWrcRjw+5Q@mail.gmail.com>
Date: Fri, 6 Feb 2026 12:04:16 +0100
From: Linus Walleij <linusw@...nel.org>
To: Billy Tsai <billy_tsai@...eedtech.com>
Cc: Tony Lindgren <tony@...mide.com>, Haojian Zhuang <haojian.zhuang@...aro.org>, 
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, 
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>, 
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"andrew@...econstruct.com.au" <andrew@...econstruct.com.au>, BMC-SW <BMC-SW@...eedtech.com>
Subject: Re: [PATCH v2 0/3] pinctrl: single: bit-per-mux DT flexibility, probe
 robustness, and consistent pinconf offsets

On Fri, Feb 6, 2026 at 8:24 AM Billy Tsai <billy_tsai@...eedtech.com> wrote:

> I understand the preference is to keep pinctrl-single minimal and move
> the bit-per-mux handling into a separate, more targeted driver built on
> top of the GENERIC_PINMUX/GENERIC_PINCONF helpers, rather than extending
> pinctrl-single itself.
>
> Based on that, I’ll look into refactoring this into a
> pinctrl-single-bit style driver that covers bit-per-mux / bit-per-pin
> layouts generically (including AST2700), while keeping pinctrl-single
> focused on the simpler register models.
>
> One additional point I’d like to raise is the handling of pre-reserved
> MMIO regions.
>
> On AST2700 systems, the SCU register range containing the pinctrl
> registers is commonly reserved by a top-level syscon node or by firmware.
> In this setup, devm_request_mem_region() can return -EBUSY even though the
> registers are valid and intended to be shared, which currently causes the
> driver to fail probing and leaves pinmux unconfigured.
>
> When moving to a separate targeted driver, would the preferred approach
> be to treat this condition as a warning and continue probing, or is there
> an alternative pattern you’d recommend for handling shared SCU-style
> register blocks in pinctrl drivers?

Can't you just base this entire driver on syscon which uses regmap-mmio
to abstract and solve this problem?

The syscon is entirely designed as a singleton owning all registers
and handing them out to subdrivers.

Yours,
Linus Walleij