Merge tag 'printk-for-7.3-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux

Pull printk fix from Petr Mladek:

 - Allow using Braille console with a serial console driver converted
   to NBCON API

* tag 'printk-for-7.3-rc7' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux:
  braille: nbcon: Allow to use a serial console with NBCON API as Braille console

7 files changed, 156 insertions, 6 deletions

diff --git a/drivers/accessibility/braille/braille_console.c b/drivers/accessibility/braille/braille_console.c
index 06b43b678d6e..5a3e375f4800 100644
--- a/drivers/accessibility/braille/braille_console.c
+++ b/drivers/accessibility/braille/braille_console.c
@@ -62,14 +62,50 @@ static void braille_write(u16 *buf)
 {
 	static u16 lastwrite[WIDTH];
 	unsigned char data[1 + 1 + 2*WIDTH + 2 + 1], csum = 0, *c;
+	struct nbcon_write_context wctxt = { };
+	unsigned long flags;
 	u16 out;
 	int i;
 
 	if (!braille_co)
 		return;
 
+	/*
+	 * Braille console is not registered in console_list. Instead, it
+	 * is integrated with VT and shows what appears on the graphical
+	 * console under console_lock(). From this POV it is a legacy
+	 * console. But it calls serial console driver which might be
+	 * converted to the NBCON API. It is similar to
+	 * nbcon_legacy_emit_next_record() except that we should try
+	 * harder to get the lock. Otherwise, the Braille device won't show
+	 * everything what is displayed on the terminal.
+	 *
+	 * In short, simulate the original locking using NBCON API.
+	 */
+	if (braille_co->flags & CON_NBCON) {
+		if (panic_on_this_cpu()) {
+			/*
+			 * This should be good enough in practice. Most/all
+			 * serial console drivers have the atomic callback.
+			 */
+			if (!braille_co->write_atomic)
+				return;
+
+			local_irq_save(flags);
+			/* NBCON API strictly requires the ownership. */
+			if (!nbcon_braille_try_acquire(braille_co, &wctxt)) {
+				local_irq_restore(flags);
+				return;
+			}
+		} else {
+			braille_co->device_lock(braille_co, &flags);
+			while (!nbcon_braille_try_acquire(braille_co, &wctxt))
+				cpu_relax();
+		}
+	}
+
 	if (!memcmp(lastwrite, buf, WIDTH * sizeof(*buf)))
-		return;
+		goto unlock_nbcon;
 	memcpy(lastwrite, buf, WIDTH * sizeof(*buf));
 
 #define SOH 1
@@ -102,7 +138,24 @@ static void braille_write(u16 *buf)
 	*c++ = csum;
 	*c++ = ETX;
 
-	braille_co->write(braille_co, data, c - data);
+	if (braille_co->flags & CON_NBCON) {
+		nbcon_write_context_set_buf(&wctxt, (char *)data, c - data);
+		if (panic_on_this_cpu())
+			braille_co->write_atomic(braille_co, &wctxt);
+		else
+			braille_co->write_thread(braille_co, &wctxt);
+	} else {
+		braille_co->write(braille_co, data, c - data);
+	}
+
+unlock_nbcon:
+	if (braille_co->flags & CON_NBCON) {
+		nbcon_braille_release(&wctxt);
+		if (panic_on_this_cpu())
+			local_irq_restore(flags);
+		else
+			braille_co->device_unlock(braille_co, flags);
+	}
 }
 
 /* Follow the VC cursor*/
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 1acb73e45f8a..b01baff71f60 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -3417,8 +3417,11 @@ static void __serial8250_console_write(struct uart_8250_port *up,
 	 * If the console printer did not fully output the previous line, it
 	 * must have been handed or taken over. Insert a newline in order to
 	 * maintain clean output.
+	 *
+	 * Braille consoles are an exception. The serial port is not used
+	 * for printk(). The driver is supposed to write exactly what it gets.
 	 */
-	if (!up->console_line_ended) {
+	if (unlikely(!up->console_line_ended && !nbcon_write_context_is_braille(wctxt))) {
 		if (use_fifo)
 			__serial8250_console_fifo_write(up, wctxt, "\n", 1);
 		else
diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index c4824c201e1c..e67f2ac454b6 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -2656,7 +2656,7 @@ pl011_console_write_atomic(struct console *co, struct nbcon_write_context *wctxt
 				uap, REG_CR);
 	}
 
-	if (!uap->console_line_ended)
+	if (unlikely(!uap->console_line_ended && !nbcon_is_braille(co)))
 		uart_console_write(&uap->port, "\n", 1, pl011_console_putchar);
 	uart_console_write(&uap->port, wctxt->outbuf, wctxt->len, pl011_console_putchar);
 
diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index 513dbe95f7e9..986fefb45c63 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -2136,7 +2136,7 @@ static void imx_uart_console_write_atomic(struct console *co,
 	imx_uart_writel(sport, ucr1, UCR1);
 	imx_uart_writel(sport, old_ucr.ucr2 | UCR2_TXEN, UCR2);
 
-	if (!sport->last_putchar_was_newline)
+	if (unlikely(!sport->last_putchar_was_newline && !nbcon_is_braille(co)))
 		uart_console_write(port, "\n", 1, imx_uart_console_putchar);
 	uart_console_write(port, wctxt->outbuf, wctxt->len,
 			   imx_uart_console_putchar);
diff --git a/drivers/tty/serial/sifive.c b/drivers/tty/serial/sifive.c
index 110d67613192..f615701fceb7 100644
--- a/drivers/tty/serial/sifive.c
+++ b/drivers/tty/serial/sifive.c
@@ -821,7 +821,7 @@ static void sifive_serial_console_write_atomic(struct console *co,
 	ier = __ssp_readl(ssp, SIFIVE_SERIAL_IE_OFFS);
 	__ssp_writel(0, SIFIVE_SERIAL_IE_OFFS, ssp);
 
-	if (!ssp->console_line_ended)
+	if (unlikely(!ssp->console_line_ended && !nbcon_is_braille(co)))
 		uart_console_write(port, "\n", 1, sifive_serial_console_putchar);
 	uart_console_write(port, wctxt->outbuf, wctxt->len,
 			   sifive_serial_console_putchar);
diff --git a/include/linux/console.h b/include/linux/console.h
index 502d1abe3f50..df23148987ee 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -615,6 +615,15 @@ extern bool nbcon_allow_unsafe_takeover(void);
 extern bool nbcon_kdb_try_acquire(struct console *con,
 				  struct nbcon_write_context *wctxt);
 extern void nbcon_kdb_release(struct nbcon_write_context *wctxt);
+extern bool nbcon_write_context_is_braille(struct nbcon_write_context *wctxt);
+extern bool nbcon_braille_try_acquire(struct console *con,
+				      struct nbcon_write_context *wctxt);
+extern void nbcon_braille_release(struct nbcon_write_context *wctxt);
+
+static inline bool nbcon_is_braille(struct console *con)
+{
+	return con && (con->flags & CON_BRL);
+}
 
 /*
  * Check if the given console is currently capable and allowed to print
@@ -678,8 +687,14 @@ static inline void nbcon_reacquire_nobuf(struct nbcon_write_context *wctxt) { }
 static inline bool nbcon_kdb_try_acquire(struct console *con,
 					 struct nbcon_write_context *wctxt) { return false; }
 static inline void nbcon_kdb_release(struct nbcon_write_context *wctxt) { }
+static inline
+bool nbcon_write_context_is_braille(struct nbcon_write_context *wctxt) { return false; }
 static inline bool console_is_usable(struct console *con, short flags,
 				     bool use_atomic) { return false; }
+static inline bool nbcon_braille_try_acquire(struct console *con,
+					     struct nbcon_write_context *wctxt) { return false; }
+static inline void nbcon_braille_release(struct nbcon_write_context *wctxt) { }
+static inline bool nbcon_is_braille(struct console *con) { return false; }
 #endif
 
 extern int console_set_on_cmdline;
diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index d17704fe93ae..fb1b37741952 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -1887,6 +1887,7 @@ bool nbcon_device_try_acquire(struct console *con)
 
 	memset(ctxt, 0, sizeof(*ctxt));
 	ctxt->console	= con;
+	/* Keep in sync with nbcon_braille_try_acquire(). */
 	ctxt->prio	= NBCON_PRIO_NORMAL;
 
 	if (!nbcon_context_try_acquire(ctxt, false))
@@ -2002,3 +2003,81 @@ void nbcon_kdb_release(struct nbcon_write_context *wctxt)
 	 */
 	__nbcon_atomic_flush_pending_con(ctxt->console, prb_next_reserve_seq(prb));
 }
+
+/**
+ * nbcon_is_braille - Checks whether the nbcon write context is using Braille console
+ *
+ * @wctxt:	checked nbcon write context
+ *
+ * Return: True when the write context is associated with a Braille console.
+ *	   Otherwise, return false.
+ *
+ * Context: Can be called in any context but only when Braille console is
+ *	registered and the struct console could not disappear.
+ */
+bool nbcon_write_context_is_braille(struct nbcon_write_context *wctxt)
+{
+	struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
+	struct console *con = ctxt->console;
+
+	return con && con->flags & CON_BRL;
+}
+EXPORT_SYMBOL_GPL(nbcon_write_context_is_braille);
+
+/**
+ * nbcon_braille_try_acquire - Try to acquire nbcon console for braille_write()
+ *
+ * @con:	The nbcon console to acquire
+ * @wctxt:	The nbcon write context to be used on success
+ *
+ * Context:	braille_write() for emitting a single buffer on Braille console.
+ *
+ * Return:	True if the console was acquired. False otherwise.
+ *
+ * Braille console is not registered as a proper printk consoles. Instead,
+ * it is integrated with the graphical virtual terminal.
+ *
+ * This function is going to synchronize the Braille write against other
+ * operations on the used serial port. The port can be used also for a user
+ * input but printk() won't emit the messages there directly. It means
+ * the other operations will get synchronized using nbcon_device_try_acquire().
+ */
+bool nbcon_braille_try_acquire(struct console *con,
+			   struct nbcon_write_context *wctxt)
+{
+	struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
+	bool success;
+
+	memset(ctxt, 0, sizeof(*ctxt));
+	ctxt->console = con;
+	/* Keep in sync with nbcon_device_try_acquire(). */
+	if (panic_on_this_cpu())
+		ctxt->prio = NBCON_PRIO_PANIC;
+	else
+		ctxt->prio = NBCON_PRIO_NORMAL;
+
+	success = nbcon_context_try_acquire(ctxt, false);
+	/*
+	 * Try hard in panic, otherwise the Braille console would
+	 * miss a text on the related VT.
+	 */
+	if (panic_on_this_cpu() && !success) {
+		ctxt->allow_unsafe_takeover = true;
+		success = nbcon_context_try_acquire(ctxt, false);
+	}
+
+	return success;
+}
+
+/**
+ * nbcon_braille_release - Release the nbcon console
+ *
+ * @wctxt:	The nbcon write context initialized by a successful
+ *		nbcon_braille_try_acquire()
+ */
+void nbcon_braille_release(struct nbcon_write_context *wctxt)
+{
+	struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
+
+	nbcon_context_release(ctxt);
+}