[PATCH 5.15 063/530] serial: 8250: Request full 16550A feature probing for OxSemi PCIe devices

[Greg Kroah-Hartman]

From: Maciej W. Rozycki <macro@xxxxxxxxxxx>

commit 00b7a4d4ee42be1c515e56cb1e8ba0f25e271d8e upstream.

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.

Fixes: 366f6c955d4d ("serial: 8250: Add proper clock handling for OxSemi PCIe devices")
Cc: stable@xxxxxxxxxxxxxxx # v5.19+
Reported-by: Anders Blomdell <anders.blomdell@xxxxxxxxxxxxxx>
Signed-off-by: Maciej W. Rozycki <macro@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/alpine.DEB.2.21.2209210005040.41633@xxxxxxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/tty/serial/8250/8250_pci.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/drivers/tty/serial/8250/8250_pci.c
+++ b/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;