serial: 8250: Let drivers request full 16550A feature probing

BugLink: https://bugs.launchpad.net/bugs/1996825
commit 9906890c89e4dbd900ed87ad3040080339a7f411 upstream.

A SERIAL_8250_16550A_VARIANTS configuration option has been recently
defined that lets one request the 8250 driver not to probe for 16550A
device features so as to reduce the driver's device startup time in
virtual machines.

Some actual hardware devices require these features to have been fully
determined however for their driver to work correctly, so define a flag
to let drivers request full 16550A feature probing on a device-by-device
basis if required regardless of the SERIAL_8250_16550A_VARIANTS option
setting chosen.

Fixes: dc56ecb81a0a ("serial: 8250: Support disabling mdelay-filled probes of 16550A variants")
Cc: stable@vger.kernel.org # v5.6+
Reported-by: Anders Blomdell <anders.blomdell@control.lth.se>
Signed-off-by: Maciej W. Rozycki <macro@orcam.me.uk>
Link: https://lore.kernel.org/r/alpine.DEB.2.21.2209202357520.41633@angie.orcam.me.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index a5496bd1b650307a0cda9c66b7a0fc9e21f4256c..b07326b718344dd02a64d5ef1dec2b41c0eb8552 100644 (file)
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1029,7 +1029,8 @@ static void autoconfig_16550a(struct uart_8250_port *up)
        up->port.type = PORT_16550A;
        up->capabilities |= UART_CAP_FIFO;
 
-       if (!IS_ENABLED(CONFIG_SERIAL_8250_16550A_VARIANTS))
+       if (!IS_ENABLED(CONFIG_SERIAL_8250_16550A_VARIANTS) &&
+           !(up->port.flags & UPF_FULL_PROBE))
                return;
 
        /*

diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index 8757b4a6be319eb35b0798393c141fc593428adc..86fa187f6d65e577c8e46553c071e90458add9ab 100644 (file)
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -100,7 +100,7 @@ struct uart_icount {
        __u32   buf_overrun;
 };
 
-typedef unsigned int __bitwise upf_t;
+typedef u64 __bitwise upf_t;
 typedef unsigned int __bitwise upstat_t;
 
 struct uart_port {
@@ -207,6 +207,7 @@ struct uart_port {
 #define UPF_FIXED_PORT         ((__force upf_t) (1 << 29))
 #define UPF_DEAD               ((__force upf_t) (1 << 30))
 #define UPF_IOREMAP            ((__force upf_t) (1 << 31))
+#define UPF_FULL_PROBE         ((__force upf_t) (1ULL << 32))
 
 #define __UPF_CHANGE_MASK      0x17fff
 #define UPF_CHANGE_MASK                ((__force upf_t) __UPF_CHANGE_MASK)