sc16is7xx driver not reading initial modem control signals

[mtnbarn]

Describe the bug

The sc16is7xx driver assumes that the modem control signals are in a off state when the driver starts. If a signal is in the on state when the driver is started, it will not be read properly until another line change occurs.

Issue applicable to all PI models

Steps to reproduce the behaviour

Put CTS into a mark condition before powering up the System, after Linux starts, read line status from the driver, it will not reflect the actual status of the CTS line

Device (s)

Raspberry Pi 2 Mod. B v1.2, Raspberry Pi 3 Mod. B

System

$ cat /etc/rpi-issue
Raspberry Pi reference 2023-05-03
Generated using pi-gen, https://github.com/RPi-Distro/pi-gen, 638c7521ee0c431fafca1e2bd4fd25705b37ea5b, stage2

$ vcgencmd version
Mar 17 2023 10:52:42
Copyright (c) 2012 Broadcom
version 82f3750a65fadae9a38077e3c2e217ad158c8d54 (clean) (release) (start)

$ uname -a
Linux raspberrypi 6.1.29-v7+ #2 SMP Sat May 27 10:04:21 PDT 2023 armv7l GNU/Linux

Logs

No response

Additional context

Patch to fix issue

--- drivers/tty/serial/sc16is7xx.c.orig 2023-05-25 11:18:26.493202230 -0700
+++ drivers/tty/serial/sc16is7xx.c 2023-06-12 15:34:26.242438742 -0700
@@ -1212,6 +1212,9 @@ static int sc16is7xx_startup(struct uart
SC16IS7XX_IER_MSI_BIT;
sc16is7xx_port_write(port, SC16IS7XX_IER_REG, val);

• /* Initialize the Modem Control signals to current status */
• one->old_mctrl = sc16is7xx_get_hwmctrl(port);
• /* Enable modem status polling */
  spin_lock_irqsave(&port->lock, flags);
  sc16is7xx_enable_ms(port);

[pelwell]

This kind of patch should really be sent upstream - it's not Pi-specific - and it looks uncontentious so it should be readily accepted. However, we do have one downstream patch that we haven't upstreamed yet, and I'm feeling generous.

If you give me a Signed-off-by: My Name <my-email-address> line I'll attribute the patch to you, otherwise I'll just mention your GitHub handle in the commit message.

[mtnbarn]

This patch sets the driver modem line state to the actual line state at driver startup.
Signed-off-by schmidt.earl.f@gmail.com
--- drivers/tty/serial/sc16is7xx.c.orig 2023-05-25 11:18:26.493202230 -0700
+++ drivers/tty/serial/sc16is7xx.c 2023-06-12 15:34:26.242438742 -0700
@@ -1212,6 +1212,9 @@ static int sc16is7xx_startup(struct uart
SC16IS7XX_IER_MSI_BIT;
sc16is7xx_port_write(port, SC16IS7XX_IER_REG, val);

• /* Initialize the Modem Control signals to current status */
• one->old_mctrl = sc16is7xx_get_hwmctrl(port);
• /* Enable modem status polling */
  spin_lock_irqsave(&port->lock, flags);
  sc16is7xx_enable_ms(port);

[pelwell]

Can I change that to:

Signed-off-by: Earl Schmidt <schmidt.earl.f@gmail.com>

?

[mtnbarn]

Yes please and thank you