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

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>

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 1d2a43214b48e6c1c459ea4f1c5e41cb6bab4c9f..48890ecc8afe295aa57e4321f6ee4af29e5d813e 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 02a4299b7d4294eaa1620190e1356d1e8a2fd837..2ae182f0f1de658b45201f0a61ce71bb44f5bc58 100644 (file)
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -422,7 +422,7 @@ 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 {
@@ -530,6 +530,7 @@ 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)