Re: [PATCH 0/9] serial: add new I/O type for SPI and I2C bus devices

[Ilpo Järvinen]

On Thu, 23 Apr 2026, Hugo Villeneuve wrote:

> Hello,
> this patch series add a new I/O type for serial devices on a SPI/I2C bus.
> 
> These changes are based on a suggestion [1] made by Ilpo Järvinen during
> past sc16is7xx driver patches review.

Hehe, I didn't even recall suggesting this (nor why) :-).

I like this series. Some, relatively minor, comments on the individual 
patches. Thanks for looking into solving this properly.

-- 
 i.

> I decided to use UPIO_BUS/SERIAL_IO_BUS names but maybe other names would
> be more appropriate:
>    UPIO_SBUS   / SERIAL_IO_SBUS
>    UPIO_SERBUS / SERIAL_IO_SERBUS
>    UPIO_EXT    / SERIAL_IO_EXT
>    UPIO_CUSTOM / SERIAL_IO_CUSTOM
>    UPIO_REGMAP / SERIAL_IO_REGMAP  /* Maybe not always true in future? */
>    ...
> 
> Tested on a imx6 board with two SC16is752 using SPI mode, and a dummy
> device-tree entry for a MAX3100:
>   dmesg -t | grep "base_baud"
>     2020000.serial: ttymxc0 at MMIO 0x2020000 (irq = 197, base_baud = 5000000) is a IMX
>     21e8000.serial: ttymxc1 at MMIO 0x21e8000 (irq = 198, base_baud = 5000000) is a IMX
>     spi1.0: ttySC0 (irq = 165, base_baud = 1500000) is a SC16IS752
>     spi1.0: ttySC1 (irq = 165, base_baud = 1500000) is a SC16IS752
>     spi3.0: ttySC2 (irq = 37, base_baud = 1500000) is a SC16IS752
>     spi3.0: ttySC3 (irq = 37, base_baud = 1500000) is a SC16IS752
>     spi3.1: ttyMAX0 (irq = 0, base_baud = 0) is a MAX3100
> Note that before these patches, max3100 silently failed in uart_configure_port()
> because membase/iobase/mapbase were zero.
>
> For max310x and SC16is7xx in i2c mode, tested only that driver is properly
> registered by using i2c-stub.
> 
> Also tested on a custom board with a Renesas RZ/G2L cpu (sh-sci driver) to
> confirm there is no regression:
>   dmesg -t | grep "base_baud"
>     1004b800.serial: ttySC0 at MMIO 0x1004b800 (irq = 35, base_baud = 0) is a scif
>     1004bc00.serial: ttySC1 at MMIO 0x1004bc00 (irq = 40, base_baud = 0) is a scif
> 
> Maybe some of the patches could be merged together, but for now I decided
> to keep them separate to help the review process.
> 
> Thank you.
> 
> [1] https://lore.kernel.org/lkml/2936e18f-44ea-faed-9fa0-2ddefe7c3194@xxxxxxxxxxxxxxx/raw
> 
> ---
> Hugo Villeneuve (9):
>       serial: core: add uart_iotype_mmio/legacy_io helper functions
>       serial: core: use uart_iotype_*() to simplify code
>       serial: 8250: use uart_iotype_*() to simplify code
>       serial: core: fix indentation/alignment
>       serial: core: add new I/O type for SPI and I2C bus devices
>       serial: core: prevent irrelevant I/O infos display for UPIO_BUS
>       serial: sc16is7xx: use new UPIO_BUS as iotype
>       serial: max310x: use new UPIO_BUS as iotype
>       serial: max3100: use new UPIO_BUS as iotype
> 
>  drivers/tty/serial/8250/8250_port.c |  33 ++--------
>  drivers/tty/serial/max3100.c        |   1 +
>  drivers/tty/serial/max310x.c        |   9 +--
>  drivers/tty/serial/sc16is7xx.c      |   9 +--
>  drivers/tty/serial/serial_core.c    | 121 ++++++++++++++++++++----------------
>  include/linux/serial_core.h         |   5 ++
>  include/uapi/linux/serial.h         |   1 +
>  7 files changed, 83 insertions(+), 96 deletions(-)
> ---
> base-commit: 2e68039281932e6dc37718a1ea7cbb8e2cda42e6
> change-id: 20260423-tty-upio-c8b66a0a593e
> 
> Best regards,
>