The S3NRN4V (e.g. on the Fairphone 6, SM7635) is an S3FWRN5-family NFC
controller that needs different bring-up, selected with a new
samsung,s3nrn4v compatible:
- It ships with working firmware behind a bootloader protocol this
driver does not implement (GET_BOOTINFO times out), so the firmware
download step is skipped. Its RF registers are (re)loaded with the
proprietary DUAL_OPTION command (the HW and SW register blobs merged
into a single stream) instead of the START/SET/STOP_RFREG sequence.
- Its reference clock speed is configured with the single-byte FW_CFG
form, sent from the ->setup hook (after CORE_RESET, before CORE_INIT).
The selector value (0x11) is taken from the vendor configuration for
this part; its encoding is not documented.
- It gates its XI clock through a CLK_REQ line: the chip drives it high
when it needs the clock, notably to synthesise the 13.56 MHz poll
carrier. Left always-on, the free-running clock never lets the chip's
TX PLL lock on a fresh start and it cannot poll (it falls back to
listen only). Service the handshake when a clk-req GPIO is described,
gating the clock on it; without one the clock stays always-on.
The variant is carried as match data by both the OF and the I2C device
id tables so the two match paths agree, and the OF table is now
referenced unconditionally for its match data, so drop the
of_match_ptr()/__maybe_unused annotations from it.
The error policy differs between the two configuration steps on purpose:
a clock misconfiguration is fatal (a ->setup failure aborts CORE_INIT),
whereas an RF-register update failure is only warned about and bring-up
continues, since the chip falls back to the RF registers programmed in
its flash and NFC may still work.
Unlike the host-endian word read in the legacy rfreg path, the
DUAL_OPTION checksum is accumulated with get_unaligned_le32() and emitted
little-endian explicitly, so it is correct regardless of CPU endianness.
Existing S3FWRN5 / S3FWRN82 setups keep the firmware-download path and
the always-on clock, unchanged.
Assisted-by: Claude:claude-opus-4-8
Assisted-by: Claude:claude-fable-5
Signed-off-by: Jorijn van der Graaf <jorijnvdgraaf@catcrafts.net>
Jorijn van der Graaf
9cd00a65e8