On Fri, Feb 6, 2026 at 8:24 AM Billy Tsai [off-list ref] wrote:

quoted

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.

Agreed that syscon/regmap would be ideal. The main issue with
pinctrl-single is that it is fundamentally MMIO-based: it always
requests and ioremaps the register range and performs raw MMIO accesses,
with no regmap integration. Adapting it to act as a syscon consumer would
require a larger architectural rework of the driver.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/pinctrl/pinctrl-single.c?h=v6.19-rc6#n230

Thanks,
Billy