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@linux.intel.com/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,
>