[PATCH AUTOSEL 6.17-6.16] mfd: simple-mfd-i2c: Add compatible strings for Layerscape QIXIS FPGA

[Sasha Levin <sashal@kernel.org>]

From: Ioana Ciornei <ioana.ciornei@nxp.com>

[ Upstream commit 81a2c31257411296862487aaade98b7d9e25dc72 ]

The QIXIS FPGA found on Layerscape boards such as LX2160AQDS, LS1028AQDS
etc deals with power-on-reset timing, muxing etc. Use the simple-mfd-i2c
as its core driver by adding its compatible string (already found in
some dt files). By using the simple-mfd-i2c driver, any child device
will have access to the i2c regmap created by it.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Link: https://lore.kernel.org/r/20250707153120.1371719-1-ioana.ciornei@nxp.com
Signed-off-by: Lee Jones <lee@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

YES

- What changed
  - Adds two OF match entries to `simple_mfd_i2c_of_match[]` so the
    `simple-mfd-i2c` driver binds to the QIXIS FPGA on Layerscape QDS
    boards:
    - `fsl,lx2160aqds-fpga`
    - `fsl,ls1028aqds-fpga`
  - Location: drivers/mfd/simple-mfd-i2c.c:96

- Why this is a bugfix (not a feature)
  - These compatibles already exist in mainline DTS and the binding
    schema, but there is no I2C driver matching them, so the node does
    not bind and its children aren’t instantiated.
    - DTS examples:
      - arch/arm64/boot/dts/freescale/fsl-lx2160a-qds.dts:263
      - arch/arm64/boot/dts/freescale/fsl-ls1028a-qds.dts:341
    - Binding: Documentation/devicetree/bindings/board/fsl,fpga-
      qixis-i2c.yaml:21
  - Without a bound parent driver, the child `reg-mux` node under the
    FPGA can’t get a regmap from its parent and won’t probe, leaving
    board muxing controls non-functional. This is a user-visible
    deficiency rather than new functionality.

- Code path and behavior after the change
  - Probe obtains match data and falls back safely when `.data` is NULL:
    - Default 8-bit register/8-bit value regmap is used when no custom
      config is provided: drivers/mfd/simple-mfd-i2c.c:41-45
    - If no MFD cells are supplied via `.data`, it populates children
      from DT: drivers/mfd/simple-mfd-i2c.c:51-53
  - The child `reg-mux` driver will successfully fetch the regmap from
    the parent if no MMIO/syscon region is present (fallback to
    `dev_get_regmap(dev->parent, NULL)`), enabling mux control:
    - drivers/mux/mmio.c:20

- Scope and risk assessment
  - Small, contained change: two ID table entries only; no logic
    changes; no ABI churn.
  - Conservative matching: only board-specific compatibles are added;
    the generic `fsl,fpga-qixis-i2c` is not matched, avoiding unintended
    binding on other QIXIS variants (e.g., PowerPC boards).
  - The default regmap path (8/8) aligns with how these DTs describe the
    QIXIS registers (e.g., `mux-reg-masks = <0x54 ...>` uses 8-bit
    offsets), so there is no width mismatch.
  - Touches MFD over I2C only; no architectural or cross-subsystem
    impact; minimal regression risk.

- Stable policy fit
  - Fixes a real, user-facing problem: existing DTs/bindings reference
    devices that currently don’t bind to any driver, leaving board-
    control functionality inoperative.
  - Change is trivial, low risk, and does not introduce features or
    architectural alterations.
  - No side effects beyond enabling the intended binding and population
    of DT-described child devices.

Given the above, this is a textbook stable backport candidate enabling
existing DT descriptions to function by adding missing compatible
strings in the driver’s match table.

 drivers/mfd/simple-mfd-i2c.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/mfd/simple-mfd-i2c.c b/drivers/mfd/simple-mfd-i2c.c
index 22159913bea03..f7798bd922224 100644
--- a/drivers/mfd/simple-mfd-i2c.c
+++ b/drivers/mfd/simple-mfd-i2c.c
@@ -99,6 +99,8 @@ static const struct of_device_id simple_mfd_i2c_of_match[] = {
 	{ .compatible = "maxim,max5970", .data = &maxim_max5970},
 	{ .compatible = "maxim,max5978", .data = &maxim_max5970},
 	{ .compatible = "maxim,max77705-battery", .data = &maxim_mon_max77705},
+	{ .compatible = "fsl,lx2160aqds-fpga" },
+	{ .compatible = "fsl,ls1028aqds-fpga" },
 	{}
 };
 MODULE_DEVICE_TABLE(of, simple_mfd_i2c_of_match);
-- 
2.51.0