linux-kernel - [PATCH 2/2] serial: 8250: Request full 16550A feature probing for OxSemi PCIe devices

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Date:   Sat, 17 Sep 2022 11:07:28 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@...am.me.uk>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>
cc:     Josh Triplett <josh@...htriplett.org>,
        Anders Blomdell <anders.blomdell@...trol.lth.se>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: [PATCH 2/2] serial: 8250: Request full 16550A feature probing for
 OxSemi PCIe devices

Oxford Semiconductor PCIe (Tornado) 950 serial port devices need to 
operate in the enhanced mode via the EFR register for the Divide-by-M 
N/8 baud rate generator prescaler to be used in their native UART mode.  
Otherwise the prescaler is fixed at 1 causing grossly incorrect baud 
rates to be programmed.

Accessing the EFR register requires 16550A features to have been probed 
for, so request this to happen regardless of SERIAL_8250_16550A_VARIANTS 
by setting UPF_FULL_PROBE in port flags.

Signed-off-by: Maciej W. Rozycki <macro@...am.me.uk>
Reported-by: Anders Blomdell <anders.blomdell@...trol.lth.se>
Fixes: 366f6c955d4d ("serial: 8250: Add proper clock handling for OxSemi PCIe devices")
Cc: stable@...r.kernel.org # v5.19+
---
 drivers/tty/serial/8250/8250_pci.c |    5 +++++
 1 file changed, 5 insertions(+)

linux-serial-8250-oxsemi-efr.diff
Index: linux-macro/drivers/tty/serial/8250/8250_pci.c
===================================================================
--- linux-macro.orig/drivers/tty/serial/8250/8250_pci.c
+++ linux-macro/drivers/tty/serial/8250/8250_pci.c
@@ -1232,6 +1232,10 @@ static void pci_oxsemi_tornado_set_mctrl
 	serial8250_do_set_mctrl(port, mctrl);
 }
 
+/*
+ * We require EFR features for clock programming, so set UPF_FULL_PROBE
+ * for full probing regardless of CONFIG_SERIAL_8250_16550A_VARIANTS setting.
+ */
 static int pci_oxsemi_tornado_setup(struct serial_private *priv,
 				    const struct pciserial_board *board,
 				    struct uart_8250_port *up, int idx)
@@ -1239,6 +1243,7 @@ static int pci_oxsemi_tornado_setup(stru
 	struct pci_dev *dev = priv->dev;
 
 	if (pci_oxsemi_tornado_p(dev)) {
+		up->port.flags |= UPF_FULL_PROBE;
 		up->port.get_divisor = pci_oxsemi_tornado_get_divisor;
 		up->port.set_divisor = pci_oxsemi_tornado_set_divisor;
 		up->port.set_mctrl = pci_oxsemi_tornado_set_mctrl;