serial: 8250: Move Alpha-specific quirk out of the core

struct uart_8250_port contains mcr_mask and mcr_force members whose
sole purpose is to work around an Alpha-specific quirk.  This code
doesn't belong in the core where it is executed by everyone else,
so move it to a proper ->set_mctrl callback which is used on the
affected Alpha machine only.

The quirk was introduced in January 1995:
https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/diff/drivers/char/serial.c?h=1.1.83

The members in struct uart_8250_port were added in 2002:
https://git.kernel.org/history/history/c/4524aad27854

The quirk applies to non-PCI Alphas and arch/alpha/Kconfig specifies
"select FORCE_PCI if !ALPHA_JENSEN".  So apparently the only affected
machine is the EISA-based Jensen that Linus was working on back then:
https://lore.kernel.org/all/CAHk-=wj1JWZ3sCrGz16nxEj7=0O+srMg6Ah3iPTDXSPKEws_SA@mail.gmail.com/

Up until now the quirk is not applied unless CONFIG_PCI is disabled.
If users forget to do that or run a generic Alpha kernel, the serial
ports aren't usable on Jensen.  Avoid by confining the quirk to
CONFIG_ALPHA_JENSEN instead of !CONFIG_PCI.  On generic Alpha kernels,
auto-detect at runtime whether the quirk needs to be applied.

Cc: Russell King <rmk+kernel@armlinux.org.uk>
Cc: Ulrich Teichert <krypton@ulrich-teichert.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Link: https://lore.kernel.org/r/b83d069cb516549b8a5420e097bb6bdd806f36fc.1640695609.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250.h

@@ -241,16 +241,8 @@ static inline int serial8250_in_MCR(struct uart_8250_port *up)
 	return mctrl;
 }
 
-#if defined(__alpha__) && !defined(CONFIG_PCI)
+bool alpha_jensen(void);
-/*
+void alpha_jensen_set_mctrl(struct uart_port *port, unsigned int mctrl);
- * Digital did something really horribly wrong with the OUT1 and OUT2
- * lines on at least some ALPHA's.  The failure mode is that if either
- * is cleared, the machine locks up with endless interrupts.
- */
-#define ALPHA_KLUDGE_MCR  (UART_MCR_OUT2 | UART_MCR_OUT1)
-#else
-#define ALPHA_KLUDGE_MCR 0
-#endif
 
 #ifdef CONFIG_SERIAL_8250_PNP
 int serial8250_pnp_init(void);

drivers/tty/serial/8250/8250_alpha.c

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+#include <asm/machvec.h>
+#include "8250.h"
+
+bool alpha_jensen(void)
+{
+	return !strcmp(alpha_mv.vector_name, "Jensen");
+}
+
+void alpha_jensen_set_mctrl(struct uart_port *port, unsigned int mctrl)
+{
+	/*
+	 * Digital did something really horribly wrong with the OUT1 and OUT2
+	 * lines on Alpha Jensen.  The failure mode is that if either is
+	 * cleared, the machine locks up with endless interrupts.
+	 */
+	mctrl |= TIOCM_OUT1 | TIOCM_OUT2;
+
+	serial8250_do_set_mctrl(port, mctrl);
+}

drivers/tty/serial/8250/8250_core.c

@@ -509,11 +509,10 @@ static void __init serial8250_isa_init_ports(void)
 
 		up->ops = &univ8250_driver_ops;
 
-		/*
+		if (IS_ENABLED(CONFIG_ALPHA_JENSEN) ||
-		 * ALPHA_KLUDGE_MCR needs to be killed.
+		    (IS_ENABLED(CONFIG_ALPHA_GENERIC) && alpha_jensen()))
-		 */
+			port->set_mctrl = alpha_jensen_set_mctrl;
-		up->mcr_mask = ~ALPHA_KLUDGE_MCR;
+
-		up->mcr_force = ALPHA_KLUDGE_MCR;
 		serial8250_set_defaults(up);
 	}
 

drivers/tty/serial/8250/8250_port.c

@@ -2026,7 +2026,7 @@ void serial8250_do_set_mctrl(struct uart_port *port, unsigned int mctrl)
 
 	mcr = serial8250_TIOCM_to_MCR(mctrl);
 
-	mcr = (mcr & up->mcr_mask) | up->mcr_force | up->mcr;
+	mcr |= up->mcr;
 
 	serial8250_out_MCR(up, mcr);
 }

drivers/tty/serial/8250/Makefile

@@ -5,6 +5,8 @@
 
 obj-$(CONFIG_SERIAL_8250)		+= 8250.o 8250_base.o
 8250-y					:= 8250_core.o
+8250-$(CONFIG_ALPHA_GENERIC)		+= 8250_alpha.o
+8250-$(CONFIG_ALPHA_JENSEN)		+= 8250_alpha.o
 8250-$(CONFIG_SERIAL_8250_PNP)		+= 8250_pnp.o
 8250_base-y				:= 8250_port.o
 8250_base-$(CONFIG_SERIAL_8250_DMA)	+= 8250_dma.o

drivers/tty/serial/sunsu.c

@@ -127,7 +127,8 @@ static void serial_out(struct uart_sunsu_port *up, int offset, int value)
 	 * gate outputs a logical one. Since we use level triggered interrupts
 	 * we have lockup and watchdog reset. We cannot mask IRQ because
 	 * keyboard shares IRQ with us (Word has it as Bob Smelik's design).
-	 * This problem is similar to what Alpha people suffer, see serial.c.
+	 * This problem is similar to what Alpha people suffer, see
+	 * 8250_alpha.c.
 	 */
 	if (offset == UART_MCR)
 		value |= UART_MCR_OUT2;

include/linux/serial_8250.h

@@ -104,8 +104,6 @@ struct uart_8250_port {
 	unsigned char		ier;
 	unsigned char		lcr;
 	unsigned char		mcr;
-	unsigned char		mcr_mask;	/* mask of user bits */
-	unsigned char		mcr_force;	/* mask of forced bits */
 	unsigned char		cur_iotype;	/* Running I/O type */
 	unsigned int		rpm_tx_active;
 	unsigned char		canary;		/* non-zero during system sleep