+CC Linus, linux-gpio, On Mon, Aug 31, 2026 at 06:01:43AM +0000, Changhuang Liang wrote: > Hi, Krzysztof > > Thanks for the review. > > > On 31/08/2026 03:35, Changhuang Liang wrote: > > > Hi, Krzysztof > > > > > > Thanks for the review. > > > > > >> On 30/08/2026 08:51, Changhuang Liang wrote: > > >>> Add driver support for JHB100 UART Routing control, allowing runtime > > >>> configuration of RX muxes between UART controllers and I/O pins. > > >>> > > >>> A sysfs interface is provided for easy checking and updating of > > >>> routing paths. > > >>> > > >>> Signed-off-by: Changhuang Liang > > >>> --- > > >>> .../sysfs-driver-starfive-jhb100-uart-routing | 45 +++ > > >>> MAINTAINERS | 7 + > > >>> drivers/soc/starfive/Kconfig | 1 + > > >>> drivers/soc/starfive/Makefile | 1 + > > >>> drivers/soc/starfive/uart-routing/Kconfig | 14 + > > >>> drivers/soc/starfive/uart-routing/Makefile | 2 + > > >>> .../uart-routing/jhb100-uart-routing.c | 262 > > >> ++++++++++++++++++ > > >>> 7 files changed, 332 insertions(+) > > >>> create mode 100644 > > >>> Documentation/ABI/testing/sysfs-driver-starfive-jhb100-uart-routing > > >>> create mode 100644 drivers/soc/starfive/uart-routing/Kconfig > > >>> create mode 100644 drivers/soc/starfive/uart-routing/Makefile > > >>> create mode 100644 > > >>> drivers/soc/starfive/uart-routing/jhb100-uart-routing.c > > >>> > > >>> diff --git > > >>> a/Documentation/ABI/testing/sysfs-driver-starfive-jhb100-uart-routin > > >>> g > > >>> b/Documentation/ABI/testing/sysfs-driver-starfive-jhb100-uart-routin > > >>> g > > >>> new file mode 100644 > > >>> index 000000000000..2844133bea1b > > >>> --- /dev/null > > >>> +++ b/Documentation/ABI/testing/sysfs-driver-starfive-jhb100-uart-ro > > >>> +++ ut > > >>> +++ ing > > >>> @@ -0,0 +1,45 @@ > > >>> +What: > > >> /sys/bus/platform/drivers/starfive-jhb100-uart-routing/\*/uart\* > > >>> +Date: August 2026 > > >>> +Contact: Changhuang Liang > > >>> +Description: Selects the RX source of the UARTx device. > > >>> + > > >>> + When read, each file shows the list of available options with > > >> currently > > >>> + selected option marked by brackets "[]". The list of available > > options > > >>> + depends on the selected file. > > >>> + > > >>> + e.g. > > >>> + cat > > >> /sys/bus/platform/drivers/starfive-jhb100-uart-routing/\*.uart-routin > > >> g/uart1 > > >>> + io0 [io1] io2 io3 io4 io5 io6 io7 io8 io9 io10 io11 io12 io13 > > >>> +io14 uart0 > > >> uart1 > > >>> + uart2 uart3 uart4 uart5 uart6 uart7 uart8 uart9 uart10 uart11 > > >>> +uart12 uart13 uart14 > > >>> + > > >>> + In this case, UART1 gets its input from IO1 (physical serial port > > 1). > > >>> + > > >>> + To switch the RX source of UART1 to UART2, write the desired > > >> source to the file: > > >>> + echo uart2 > > > >>> +/sys/bus/platform/drivers/starfive-jhb100-uart-routing/*.uart-routi > > >>> +ng > > >>> +/uart1 > > >>> + > > >>> + This indicates that UART1 now receives its input from UART2. > > >>> + > > >>> +Users: OpenBMC. Proposed changes should be mailed to > > >>> + openbmc@lists.ozlabs.org > > >>> + > > >>> +What: > > /sys/bus/platform/drivers/starfive-jhb100-uart-routing/\*/io\* > > >>> +Date: August 2026 > > >>> +Contact: Changhuang Liang > > >>> +Description: Selects the RX source of IOx serial port. The current > > >> selection > > >>> + will be marked by brackets "[]". The list of available options > > >>> + depends on the selected file. > > >>> + > > >>> + e.g. > > >>> + cat > > >> /sys/bus/platform/drivers/starfive-jhb100-uart-routing/\*.uart-routin > > >> g/io9 > > >>> + uart0 uart1 uart2 uart3 uart4 uart5 uart6 uart7 uart8 [uart9] > > >>> +uart10 > > >> uart11 uart12 > > >>> + uart13 uart14 io0 io1 io2 io3 io4 io5 io6 io7 io8 io9 io10 io11 > > >>> +io12 io13 io14 > > >>> + > > >>> + In this case, IO9 (physical serial port 9) gets its input from > > UART9. > > >>> + > > >>> + To switch the RX source of IO9 to UART10, write the desired > > >>> +source > > >> to the file: > > >>> + echo uart10 > > > >>> +/sys/bus/platform/drivers/starfive-jhb100-uart-routing/*.uart-routi > > >>> +ng > > >>> +/io9 > > >>> + > > >>> + This indicates that IO9 now receives its input from UART10. > > >>> + > > >>> +Users: OpenBMC. Proposed changes should be mailed to > > >>> + openbmc@lists.ozlabs.org > > >> > > >> drivers/soc/ should not define user-space interfaces. This is not the > > >> place for them. You need to route user-spaces interfaces only through > > >> one of other approved subsystems, after their review. > > >> > > >> This looks like pin multiplexing interface. > > > > > > I may have misunderstood somethingļ¼Œplease correct me if I'm wrong: > > > > > > I have found two subsystems related to multiplexing so far: > > > > > > /drivers/pinctrl and /drivers/mux. However, neither of them seems to > > > provide a user-space interface for switching multiplexing values. > > > > > > Do you have any suggestions on this? > > > > pinctrl has some interface, not sure if writable, though. If interface is missing, > > it should be added via such subsystem. > > Okay, this needs a bit more time for deeper research. > > > > > > > > > Also, could you confirm whether the implementation in > > > drivers/soc/aspeed/aspeed-uart-routing.c > > > is there for historical reasons? > > > > I supposed sneaked in without SoC maintainers noticing. My first reaction when this flew by over the weekend was whether it should be in the pinctrl subsystem. I know there's no sysfs interface there, but I don't even see an explanation for why changing this at runtime is a requirement. I'd have thought that each BMC would only have one host, and so since you've got like 12 uarts there'd be enough for a permanent routing. Even without a permanent routing, the driver consuming the pinctrl should be able perform the switching (uart in this case) whenever it was needed? Cheers, Conor.