Feature request - Add a module for sc16is752 to the standard configurations

[MasterWuff]

Hi,

Recently I had a problem when I was switching from RPi2 to RPi3, because of only one UART interface. Never the less, I decided to buy a SC16IS752 from NXP. It can connected it to the RPi via I2C and SPI. The external interfaces are two UART ports and 8 GPIOs.

But here is the problem, the module isn't in the standard configurations to work with that.
There is the solution to complile the kernel, but I don't feel really confident with that.

Why to add the module?
-The code already exists: https://github.com/raspberrypi/linux/blob/rpi-4.1.y/drivers/tty/serial/sc16is7xx.c
-The overlay already exists (/boot/overlays/sc16is752-spi1.dtbo)
-It is only 24kB
-i'm not the only one who is dealing with one UART interface

Thanks in advance and on spending so much time to keep the system up to date.

[pelwell]

It's fine with me. @popcornmix?

[popcornmix]

Okay.

[popcornmix]

This is now in latest rpi-update kernel.

[MasterWuff]

Thanks a lot, this is what I call a support. Less then 24 hours.
Short Feedback: it works GREAT

[popcornmix]

Cool. Feel free to close the issue.

[DimionDR]

Hello!
Why I2C drivers implementation?!!
Overlay file only for SPI - /boot/overlays/sc16is752-spi1.dtbo

[MasterWuff]

Hi DimionDR,
the kernel add on is for I2C and SPI. By default there is one overlay for a SPI connection, but you can write your own for I2C. Or have a look here: https://www.raspberrypi.org/forums/viewtopic.php?f=107&t=146908&start=25
You can use both

[DimionDR]

Hello,
I am new in DTS, is it possible to change working interface for the sc16is7xx module without recompiling? My problem is what I want to use the module with SPI...
modinfo output:
pi@raspberrypi:~ $ modinfo sc16is7xx
filename: /lib/modules/4.4.17-v7+/kernel/drivers/tty/serial/sc16is7xx.ko
description: SC16IS7XX serial driver
author: Jon Ringle jringle@gridpoint.com
license: GPL
srcversion: 2021DCD9C98A4797C2CB85D
alias: of:N_T_Cnxp,sc16is762*
alias: of:N_T_Cnxp,sc16is760*
alias: of:N_T_Cnxp,sc16is752*
alias: of:N_T_Cnxp,sc16is750*
alias: of:N_T_Cnxp,sc16is741*
alias: of:N_T_Cnxp,sc16is740*
alias: i2c:sc16is762
alias: i2c:sc16is760
alias: i2c:sc16is752
alias: i2c:sc16is750
alias: i2c:sc16is741
alias: i2c:sc16is740
alias: i2c:sc16is74x
depends: regmap-i2c
intree: Y
vermagic: 4.4.17-v7+ SMP mod_unload modversions ARMv7

[MasterWuff]

I'm sorry, I didn't get the file working with SPI. With i2c it works, but to be honest, the commends to controll the chip are missing (like setting bau drate or gpios). I know how to write to the registers with I2C or SPI, but the overlay was too much for my knowledge. Perhaps someone else has more experience and will complete the work and thread in the forum. To spend nearly two weeks on such a small issue is too long.

[pelwell]

What @DimionDR has spotted is that the config change only enables support for the I2C interface, not the SPI mode, which explains the behaviour you are seeing:

$ grep SC16 .config
CONFIG_SERIAL_SC16IS7XX_CORE=m
CONFIG_SERIAL_SC16IS7XX=m
CONFIG_SERIAL_SC16IS7XX_I2C=y
# CONFIG_SERIAL_SC16IS7XX_SPI is not set

I'll reopen this until SERIAL_SC16IS7XX_SPI is also defined.

[MasterWuff]

Okay, my fault. I will edit the thread in the forum