[PATCH AUTOSEL 5.4 032/266] serial: 8250: Fix max baud limit in generic 8250 port

[PATCH AUTOSEL 5.4 032/266] serial: 8250: Fix max baud limit in generic 8250 port

[Sasha Levin]

From: Serge Semin <Sergey.Semin@baikalelectronics.ru>

[ Upstream commit 7b668c064ec33f3d687c3a413d05e355172e6c92 ]

Standard 8250 UART ports are designed in a way so they can communicate
with baud rates up to 1/16 of a reference frequency. It's expected from
most of the currently supported UART controllers. That's why the former
version of serial8250_get_baud_rate() method called uart_get_baud_rate()
with min and max baud rates passed as (port->uartclk / 16 / UART_DIV_MAX)
and ((port->uartclk + tolerance) / 16) respectively. Doing otherwise, like
it was suggested in commit ("serial: 8250_mtk: support big baud rate."),
caused acceptance of bauds, which was higher than the normal UART
controllers actually supported. As a result if some user-space program
requested to set a baud greater than (uartclk / 16) it would have been
permitted without truncation, but then serial8250_get_divisor(baud)
(which calls uart_get_divisor() to get the reference clock divisor) would
have returned a zero divisor. Setting zero divisor will cause an
unpredictable effect varying from chip to chip. In case of DW APB UART the
communications just stop.

Lets fix this problem by getting back the limitation of (uartclk +
tolerance) / 16 maximum baud supported by the generic 8250 port. Mediatek
8250 UART ports driver developer shouldn't have touched it in the first
place  notably seeing he already provided a custom version of set_termios()
callback in that glue-driver which took into account the extended baud
rate values and accordingly updated the standard and vendor-specific
divisor latch registers anyway.

Fixes: 81bb549fdf14 ("serial: 8250_mtk: support big baud rate.")
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Paul Burton <paulburton@kernel.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Long Cheng <long.cheng@mediatek.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Russell King <linux@armlinux.org.uk>
Cc: linux-mips@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-mediatek@lists.infradead.org
Link: https://lore.kernel.org/r/20200506233136.11842-2-Sergey.Semin@baikalelectronics.ru
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/tty/serial/8250/8250_port.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 2c65c775bf5a..dbb27303a6b4 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -2539,6 +2539,8 @@ static unsigned int serial8250_get_baud_rate(struct uart_port *port,
 					     struct ktermios *termios,
 					     struct ktermios *old)
 {
+	unsigned int tolerance = port->uartclk / 100;
+
 	/*
 	 * Ask the core to calculate the divisor for us.
 	 * Allow 1% tolerance at the upper limit so uart clks marginally
@@ -2547,7 +2549,7 @@ static unsigned int serial8250_get_baud_rate(struct uart_port *port,
 	 */
 	return uart_get_baud_rate(port, termios, old,
 				  port->uartclk / 16 / UART_DIV_MAX,
-				  port->uartclk);
+				  (port->uartclk + tolerance) / 16);
 }
 
 void
-- 
2.25.1

[PATCH AUTOSEL 5.4 122/266] serial: amba-pl011: Make sure we initialize the port.lock spinlock

[Sasha Levin]

From: John Stultz <john.stultz@linaro.org>

[ Upstream commit 8508f4cba308f785b2fd4b8c38849c117b407297 ]

Valentine reported seeing:

[    3.626638] INFO: trying to register non-static key.
[    3.626639] the code is fine but needs lockdep annotation.
[    3.626640] turning off the locking correctness validator.
[    3.626644] CPU: 7 PID: 51 Comm: kworker/7:1 Not tainted 5.7.0-rc2-00115-g8c2e9790f196 #116
[    3.626646] Hardware name: HiKey960 (DT)
[    3.626656] Workqueue: events deferred_probe_work_func
[    3.632476] sd 0:0:0:0: [sda] Optimal transfer size 8192 bytes not a multiple of physical block size (16384 bytes)
[    3.640220] Call trace:
[    3.640225]  dump_backtrace+0x0/0x1b8
[    3.640227]  show_stack+0x20/0x30
[    3.640230]  dump_stack+0xec/0x158
[    3.640234]  register_lock_class+0x598/0x5c0
[    3.640235]  __lock_acquire+0x80/0x16c0
[    3.640236]  lock_acquire+0xf4/0x4a0
[    3.640241]  _raw_spin_lock_irqsave+0x70/0xa8
[    3.640245]  uart_add_one_port+0x388/0x4b8
[    3.640248]  pl011_register_port+0x70/0xf0
[    3.640250]  pl011_probe+0x184/0x1b8
[    3.640254]  amba_probe+0xdc/0x180
[    3.640256]  really_probe+0xe0/0x338
[    3.640257]  driver_probe_device+0x60/0xf8
[    3.640259]  __device_attach_driver+0x8c/0xd0
[    3.640260]  bus_for_each_drv+0x84/0xd8
[    3.640261]  __device_attach+0xe4/0x140
[    3.640263]  device_initial_probe+0x1c/0x28
[    3.640265]  bus_probe_device+0xa4/0xb0
[    3.640266]  deferred_probe_work_func+0x7c/0xb8
[    3.640269]  process_one_work+0x2c0/0x768
[    3.640271]  worker_thread+0x4c/0x498
[    3.640272]  kthread+0x14c/0x158
[    3.640275]  ret_from_fork+0x10/0x1c

Which seems to be due to the fact that after allocating the uap
structure, nothing initializes the spinlock.

Its a little confusing, as uart_port_spin_lock_init() is one
place where the lock is supposed to be initialized, but it has
an exception for the case where the port is a console.

This makes it seem like a deeper fix is needed to properly
register the console, but I'm not sure what that entails, and
Andy suggested that this approach is less invasive.

Thus, this patch resolves the issue by initializing the spinlock
in the driver, and resolves the resulting warning.

Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: linux-serial@vger.kernel.org
Reported-by: Valentin Schneider <valentin.schneider@arm.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Reviewed-and-tested-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lore.kernel.org/r/20200428184050.6501-1-john.stultz@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/tty/serial/amba-pl011.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index b0b689546395..de3e8c24c03e 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -2585,6 +2585,7 @@ static int pl011_setup_port(struct device *dev, struct uart_amba_port *uap,
 	uap->port.fifosize = uap->fifosize;
 	uap->port.flags = UPF_BOOT_AUTOCONF;
 	uap->port.line = index;
+	spin_lock_init(&uap->port.lock);
 
 	amba_ports[index] = uap;
 
-- 
2.25.1