drivers: PL011: allow avoiding UART enabling/disabling

The SBSA UART should not be enabled or disabled (it is always on),
and consequently the spec lacks the UART_CR register.
Add a vendor specific property to skip disabling or enabling of the
UART. This will be used later by the SBSA UART support.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Tested-by: Mark Langsdorf <mlangsdo@redhat.com>
Tested-by: Naresh Bhat <nbhat@cavium.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/amba-pl011.c

@@ -78,6 +78,7 @@ struct vendor_data {
 	bool			oversampling;
 	bool			dma_threshold;
 	bool			cts_event_workaround;
+	bool			always_enabled;
 
 	unsigned int (*get_fifosize)(struct amba_device *dev);
 };
@@ -94,6 +95,7 @@ static struct vendor_data vendor_arm = {
 	.oversampling		= false,
 	.dma_threshold		= false,
 	.cts_event_workaround	= false,
+	.always_enabled		= false,
 	.get_fifosize		= get_fifosize_arm,
 };
 
@@ -109,6 +111,7 @@ static struct vendor_data vendor_st = {
 	.oversampling		= true,
 	.dma_threshold		= true,
 	.cts_event_workaround	= true,
+	.always_enabled		= false,
 	.get_fifosize		= get_fifosize_st,
 };
 
@@ -1958,7 +1961,7 @@ static void
 pl011_console_write(struct console *co, const char *s, unsigned int count)
 {
 	struct uart_amba_port *uap = amba_ports[co->index];
-	unsigned int status, old_cr, new_cr;
+	unsigned int status, old_cr = 0, new_cr;
 	unsigned long flags;
 	int locked = 1;
 
@@ -1975,10 +1978,12 @@ pl011_console_write(struct console *co, const char *s, unsigned int count)
 	/*
 	 *	First save the CR then disable the interrupts
 	 */
-	old_cr = readw(uap->port.membase + UART011_CR);
-	new_cr = old_cr & ~UART011_CR_CTSEN;
-	new_cr |= UART01x_CR_UARTEN | UART011_CR_TXE;
-	writew(new_cr, uap->port.membase + UART011_CR);
+	if (!uap->vendor->always_enabled) {
+		old_cr = readw(uap->port.membase + UART011_CR);
+		new_cr = old_cr & ~UART011_CR_CTSEN;
+		new_cr |= UART01x_CR_UARTEN | UART011_CR_TXE;
+		writew(new_cr, uap->port.membase + UART011_CR);
+	}
 
 	uart_console_write(&uap->port, s, count, pl011_console_putchar);
 
@@ -1989,7 +1994,8 @@ pl011_console_write(struct console *co, const char *s, unsigned int count)
 	do {
 		status = readw(uap->port.membase + UART01x_FR);
 	} while (status & UART01x_FR_BUSY);
-	writew(old_cr, uap->port.membase + UART011_CR);
+	if (!uap->vendor->always_enabled)
+		writew(old_cr, uap->port.membase + UART011_CR);
 
 	if (locked)
 		spin_unlock(&uap->port.lock);