[PATCH v5 00/11] drivers: PL011: add ARM SBSA Generic UART support

[PATCH v5 00/11] drivers: PL011: add ARM SBSA Generic UART support

[Andre Przywara]

This is the fifth revision of the SBSA UART support series, based on
the current tty-next branch.
Beside some minor formatting issues fixed (thanks ot Jakub for
noticing) the SBSA UART set_termios() function has been reworked.
We now completely ignore the old value, instead we filter the new
setting to match the SBSA UART's fixed parameters for word size,
parity, stop bits and so on.
This should also address the issues people have seen with ACPI on
Fedora systems.
Mark, Naresh, Graeme: can you confirm that this version works for
you? If needed I can bake a follow-up patch on top of v4.
----

The ARM Server Base System Architecture[1] document describes a
generic UART which is a subset of the ARM PL011 UART.
It lacks DMA support, baud rate control and modem status line
control, among other things.
The idea is to move the UART initialization and setup into the
firmware (which does this job today already) and let the kernel just
use the UART for sending and receiving characters.

This patchset integrates support for this UART subset into the
existing PL011 driver - basically by refactoring some
functions and providing a new uart_ops structure for it. It also has
a separate probe function to be not dependent on AMBA/PrimeCell.
It provides a device tree and an ACPI binding.
Beside the obvious effect of code sharing reusing most of the PL011
code has the advantage of not introducing another serial device
prefix, so it can go with ttyAMA, which seems to be pretty common.
As changing the baudrate and other communication parameters is not
specified for the SBSA UART, any userland attempt will be denied by
the kernel. The device-tree provided fixed baud rate will be
reported, so stty for instance prints the right value.

This series is based on Greg's tty-next branch, a git repo can
be found at [2] (branch sbsa-uart/v5).

Patch 1/11 contains a bug fix which applies to the PL011 part also,
it should be considered regardless of the rest of the series.
According to Russell this is still racy, but still better than the
current solution.
Patch 2-7 refactor some PL011 functions by splitting them up into
smaller pieces, so that most of the code can be reused later by the
SBSA part.
Patch 8 and 9 introduce two new properties for the vendor structure,
this is for SBSA functionality which cannot be controlled by
separate uart_ops members only.
Patch 10 then finally drops in the SBSA specific code, by providing
a new uart_ops, vendor struct and probe function for it. Also the new
device tree binding is documented.
Patch 11 adds the necessary ACPI boilerplate.

For testing you should be able to take any hardware which has a PL011
and change the DT to use a "arm,sbsa-uart" compatible string and the
baud rate with the "current-speed" property.
Of course testing with a real SBSA Generic UART is welcomed - as well
as regression testing with any PL011 implementation.
I tested this on a FastModel, a Juno and a Midway machine, both in
PL011 and in (DT-emulated) SBSA mode.

Tested-by: Robert Richter <rrichter@cavium.com>
Tested-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Tested-by: Hanjun Guo <hanjun.guo@linaro.org>

Changelog:
v4 .. v5:
- fixed checkpatch --strict complaints
- rework set_termios:
  - disallow changes or UART fixed communication parameters
  - ignore old value to fix an issue with Fedora on ACPI

v3 .. v4:
- fixed rebase artifact
- moved memory allocation out of pl011_allocate_port() function
  (and consequently renamed that to pl011_find_free_port)
- added ACPI driver binding

v2 .. v3:
- rebased on top of tty-next and Dave's latest PL011 rework
- fixed module build
- removed redundant =NULL members in sbsa_uart_ops

v1 .. v2:
- rebased on top of 4.0-rc1 and Dave's newest PL011 fix [3]
- added mandatory current-speed property and report that to userland

Cheers,
Andre

[1] ARM-DEN-0029 Server Base System Architecture, available (click-
    thru...) from http://infocenter.arm.com
[2] http://www.linux-arm.org/git?p=linux-ap.git
    git://linux-arm.org/linux-ap.git
[3] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-March/327631.html

Andre Przywara (10):
  drivers: PL011: avoid potential unregister_driver call
  drivers: PL011: refactor pl011_startup()
  drivers: PL011: refactor pl011_shutdown()
  drivers: PL011: refactor pl011_set_termios()
  drivers: PL011: refactor pl011_probe()
  drivers: PL011: replace UART_MIS reading with _RIS & _IMSC
  drivers: PL011: move cts_event workaround into separate function
  drivers: PL011: allow avoiding UART enabling/disabling
  drivers: PL011: allow to supply fixed option string
  drivers: PL011: add support for the ARM SBSA generic UART

Graeme Gregory (1):
  drivers: PL011: add ACPI probing for SBSA UART

 .../devicetree/bindings/serial/arm_sbsa_uart.txt   |  10 +
 drivers/tty/serial/amba-pl011.c                    | 550 +++++++++++++++------
 2 files changed, 412 insertions(+), 148 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/serial/arm_sbsa_uart.txt

-- 
2.3.5

[PATCH v5 01/11] drivers: PL011: avoid potential unregister_driver call

[Andre Przywara]

Although we care about not unregistering the driver if there are
still ports connected during the .remove callback, we do miss this
check in the pl011_probe function. So if the current port allocation
fails, but there are other ports already registered, we will kill
those.
So factor out the port removal into a separate function and use that
in the probe function, too.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/tty/serial/amba-pl011.c | 36 ++++++++++++++++++++----------------
 1 file changed, 20 insertions(+), 16 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index f5bd842..b4de23c 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -2135,6 +2135,23 @@ static int pl011_probe_dt_alias(int index, struct device *dev)
 	return ret;
 }
 
+/* unregisters the driver also if no more ports are left */
+static void pl011_unregister_port(struct uart_amba_port *uap)
+{
+	int i;
+	bool busy = false;
+
+	for (i = 0; i < ARRAY_SIZE(amba_ports); i++) {
+		if (amba_ports[i] == uap)
+			amba_ports[i] = NULL;
+		else if (amba_ports[i])
+			busy = true;
+	}
+	pl011_dma_remove(uap);
+	if (!busy)
+		uart_unregister_driver(&amba_reg);
+}
+
 static int pl011_probe(struct amba_device *dev, const struct amba_id *id)
 {
 	struct uart_amba_port *uap;
@@ -2200,10 +2217,8 @@ static int pl011_probe(struct amba_device *dev, const struct amba_id *id)
 	}
 
 	ret = uart_add_one_port(&amba_reg, &uap->port);
-	if (ret) {
-		amba_ports[i] = NULL;
-		uart_unregister_driver(&amba_reg);
-	}
+	if (ret)
+		pl011_unregister_port(uap);
 
 	return ret;
 }
@@ -2211,20 +2226,9 @@ static int pl011_probe(struct amba_device *dev, const struct amba_id *id)
 static int pl011_remove(struct amba_device *dev)
 {
 	struct uart_amba_port *uap = amba_get_drvdata(dev);
-	bool busy = false;
-	int i;
 
 	uart_remove_one_port(&amba_reg, &uap->port);
-
-	for (i = 0; i < ARRAY_SIZE(amba_ports); i++)
-		if (amba_ports[i] == uap)
-			amba_ports[i] = NULL;
-		else if (amba_ports[i])
-			busy = true;
-
-	pl011_dma_remove(uap);
-	if (!busy)
-		uart_unregister_driver(&amba_reg);
+	pl011_unregister_port(uap);
 	return 0;
 }
 
-- 
2.3.5

[PATCH v5 02/11] drivers: PL011: refactor pl011_startup()

[Andre Przywara]

Split the pl011_startup() function into smaller chunks to allow
easier reuse later when adding SBSA support.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/tty/serial/amba-pl011.c | 48 ++++++++++++++++++++++++-----------------
 1 file changed, 28 insertions(+), 20 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index b4de23c..209aeb6 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1556,6 +1556,32 @@ static void pl011_write_lcr_h(struct uart_amba_port *uap, unsigned int lcr_h)
 	}
 }
 
+static int pl011_allocate_irq(struct uart_amba_port *uap)
+{
+	writew(uap->im, uap->port.membase + UART011_IMSC);
+
+	return request_irq(uap->port.irq, pl011_int, 0, "uart-pl011", uap);
+}
+
+/*
+ * Enable interrupts, only timeouts when using DMA
+ * if initial RX DMA job failed, start in interrupt mode
+ * as well.
+ */
+static void pl011_enable_interrupts(struct uart_amba_port *uap)
+{
+	spin_lock_irq(&uap->port.lock);
+
+	/* Clear out any spuriously appearing RX interrupts */
+	writew(UART011_RTIS | UART011_RXIS,
+	       uap->port.membase + UART011_ICR);
+	uap->im = UART011_RTIM;
+	if (!pl011_dma_rx_running(uap))
+		uap->im |= UART011_RXIM;
+	writew(uap->im, uap->port.membase + UART011_IMSC);
+	spin_unlock_irq(&uap->port.lock);
+}
+
 static int pl011_startup(struct uart_port *port)
 {
 	struct uart_amba_port *uap =
@@ -1567,12 +1593,7 @@ static int pl011_startup(struct uart_port *port)
 	if (retval)
 		goto clk_dis;
 
-	writew(uap->im, uap->port.membase + UART011_IMSC);
-
-	/*
-	 * Allocate the IRQ
-	 */
-	retval = request_irq(uap->port.irq, pl011_int, 0, "uart-pl011", uap);
+	retval = pl011_allocate_irq(uap);
 	if (retval)
 		goto clk_dis;
 
@@ -1595,20 +1616,7 @@ static int pl011_startup(struct uart_port *port)
 	/* Startup DMA */
 	pl011_dma_startup(uap);
 
-	/*
-	 * Finally, enable interrupts, only timeouts when using DMA
-	 * if initial RX DMA job failed, start in interrupt mode
-	 * as well.
-	 */
-	spin_lock_irq(&uap->port.lock);
-	/* Clear out any spuriously appearing RX interrupts */
-	 writew(UART011_RTIS | UART011_RXIS,
-		uap->port.membase + UART011_ICR);
-	uap->im = UART011_RTIM;
-	if (!pl011_dma_rx_running(uap))
-		uap->im |= UART011_RXIM;
-	writew(uap->im, uap->port.membase + UART011_IMSC);
-	spin_unlock_irq(&uap->port.lock);
+	pl011_enable_interrupts(uap);
 
 	return 0;
 
-- 
2.3.5

Re: [PATCH v5 02/11] drivers: PL011: refactor pl011_startup()

[Timur Tabi]

On Thu, May 21, 2015 at 11:26 AM, Andre Przywara <andre.przywara@arm.com> wrote:
> +static void pl011_enable_interrupts(struct uart_amba_port *uap)
> +{
> +       spin_lock_irq(&uap->port.lock);
> +
> +       /* Clear out any spuriously appearing RX interrupts */
> +       writew(UART011_RTIS | UART011_RXIS,
> +              uap->port.membase + UART011_ICR);
> +       uap->im = UART011_RTIM;
> +       if (!pl011_dma_rx_running(uap))
> +               uap->im |= UART011_RXIM;
> +       writew(uap->im, uap->port.membase + UART011_IMSC);
> +       spin_unlock_irq(&uap->port.lock);
> +}

Shouldn't this function be using spin_lock_irqsave() and
spin_unlock_irqrestore()?  If interrupts are generally disabled before
calling this function, then they will be enabled by the
spin_unlock_irq() call, and I don't think we want that.  This function
is only supposed to enable pl011 interrupts, not all interrupts.

-- 
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.

Re: [PATCH v5 02/11] drivers: PL011: refactor pl011_startup()

[Andre Przywara]

Hi Timur,

On 25/09/15 00:11, Timur Tabi wrote:
> On Thu, May 21, 2015 at 11:26 AM, Andre Przywara <andre.przywara@arm.com> wrote:
>> +static void pl011_enable_interrupts(struct uart_amba_port *uap)
>> +{
>> +       spin_lock_irq(&uap->port.lock);
>> +
>> +       /* Clear out any spuriously appearing RX interrupts */
>> +       writew(UART011_RTIS | UART011_RXIS,
>> +              uap->port.membase + UART011_ICR);
>> +       uap->im = UART011_RTIM;
>> +       if (!pl011_dma_rx_running(uap))
>> +               uap->im |= UART011_RXIM;
>> +       writew(uap->im, uap->port.membase + UART011_IMSC);
>> +       spin_unlock_irq(&uap->port.lock);
>> +}
> 
> Shouldn't this function be using spin_lock_irqsave() and
> spin_unlock_irqrestore()?  If interrupts are generally disabled before
> calling this function, then they will be enabled by the
> spin_unlock_irq() call, and I don't think we want that.  This function
> is only supposed to enable pl011 interrupts, not all interrupts.

Are you seeing an actual issue with this? Does changing it fix anything?
Looking at the history I see that these locks predate git history.
If I get this correctly, going from spin_{un,}lock_irq to the _irqsave
variants should always be safe, but I'd like to hear more opinions on this.

Cheers,
Andre.

Re: [PATCH v5 02/11] drivers: PL011: refactor pl011_startup()

[Russell King - ARM Linux]

On Fri, Sep 25, 2015 at 04:21:48PM +0100, Andre Przywara wrote:
> Hi Timur,
> 
> On 25/09/15 00:11, Timur Tabi wrote:
> > On Thu, May 21, 2015 at 11:26 AM, Andre Przywara <andre.przywara@arm.com> wrote:
> >> +static void pl011_enable_interrupts(struct uart_amba_port *uap)
> >> +{
> >> +       spin_lock_irq(&uap->port.lock);
> >> +
> >> +       /* Clear out any spuriously appearing RX interrupts */
> >> +       writew(UART011_RTIS | UART011_RXIS,
> >> +              uap->port.membase + UART011_ICR);
> >> +       uap->im = UART011_RTIM;
> >> +       if (!pl011_dma_rx_running(uap))
> >> +               uap->im |= UART011_RXIM;
> >> +       writew(uap->im, uap->port.membase + UART011_IMSC);
> >> +       spin_unlock_irq(&uap->port.lock);
> >> +}
> > 
> > Shouldn't this function be using spin_lock_irqsave() and
> > spin_unlock_irqrestore()?  If interrupts are generally disabled before
> > calling this function, then they will be enabled by the
> > spin_unlock_irq() call, and I don't think we want that.  This function
> > is only supposed to enable pl011 interrupts, not all interrupts.
> 
> Are you seeing an actual issue with this? Does changing it fix anything?
> Looking at the history I see that these locks predate git history.
> If I get this correctly, going from spin_{un,}lock_irq to the _irqsave
> variants should always be safe, but I'd like to hear more opinions on this.

If code is only called from process sleepable context, then using the
_irq variants is a sane thing to do, and avoids the extra work to
read and store the interrupt state prior to the protected code.
Currently that's true in mainline.

I'd encourage people not to jump on the "you're using _irq variants,
the code must be bad!" wagon, and instead spend time reading the code
and checking whether it's safe.

If the code path is suitable for a mutex, it's suitable for _irq()
variants too: you're not allowed to sleep with IRQs disabled.

If you want to have some runtime validation, add WARN_ON(!irqs_disabled());
before it, but I'd recommend against littering mainline with that.
Arguably, it's something that the _irq() variants should do, and I
think it's been proposed in the past, but rejected.  I forget why.

-- 
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.

[PATCH v5 03/11] drivers: PL011: refactor pl011_shutdown()

[Andre Przywara]

Split the pl011_shutdown() function into smaller chunks to allow
easier reuse later when adding SBSA support.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/tty/serial/amba-pl011.c | 57 +++++++++++++++++++++++------------------
 1 file changed, 32 insertions(+), 25 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 209aeb6..a43039d 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1635,34 +1635,15 @@ static void pl011_shutdown_channel(struct uart_amba_port *uap,
       writew(val, uap->port.membase + lcrh);
 }
 
-static void pl011_shutdown(struct uart_port *port)
+/*
+ * disable the port. It should not disable RTS and DTR.
+ * Also RTS and DTR state should be preserved to restore
+ * it during startup().
+ */
+static void pl011_disable_uart(struct uart_amba_port *uap)
 {
-	struct uart_amba_port *uap =
-	    container_of(port, struct uart_amba_port, port);
 	unsigned int cr;
 
-	/*
-	 * disable all interrupts
-	 */
-	spin_lock_irq(&uap->port.lock);
-	uap->im = 0;
-	writew(uap->im, uap->port.membase + UART011_IMSC);
-	writew(0xffff, uap->port.membase + UART011_ICR);
-	spin_unlock_irq(&uap->port.lock);
-
-	pl011_dma_shutdown(uap);
-
-	/*
-	 * Free the interrupt
-	 */
-	free_irq(uap->port.irq, uap);
-
-	/*
-	 * disable the port
-	 * disable the port. It should not disable RTS and DTR.
-	 * Also RTS and DTR state should be preserved to restore
-	 * it during startup().
-	 */
 	uap->autorts = false;
 	spin_lock_irq(&uap->port.lock);
 	cr = readw(uap->port.membase + UART011_CR);
@@ -1678,6 +1659,32 @@ static void pl011_shutdown(struct uart_port *port)
 	pl011_shutdown_channel(uap, uap->lcrh_rx);
 	if (uap->lcrh_rx != uap->lcrh_tx)
 		pl011_shutdown_channel(uap, uap->lcrh_tx);
+}
+
+static void pl011_disable_interrupts(struct uart_amba_port *uap)
+{
+	spin_lock_irq(&uap->port.lock);
+
+	/* mask all interrupts and clear all pending ones */
+	uap->im = 0;
+	writew(uap->im, uap->port.membase + UART011_IMSC);
+	writew(0xffff, uap->port.membase + UART011_ICR);
+
+	spin_unlock_irq(&uap->port.lock);
+}
+
+static void pl011_shutdown(struct uart_port *port)
+{
+	struct uart_amba_port *uap =
+		container_of(port, struct uart_amba_port, port);
+
+	pl011_disable_interrupts(uap);
+
+	pl011_dma_shutdown(uap);
+
+	free_irq(uap->port.irq, uap);
+
+	pl011_disable_uart(uap);
 
 	/*
 	 * Shut down the clock producer
-- 
2.3.5

[PATCH v5 04/11] drivers: PL011: refactor pl011_set_termios()

[Andre Przywara]

Split the pl011_set_termios() function into smaller chunks to allow
easier reuse later when adding SBSA support.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/tty/serial/amba-pl011.c | 60 ++++++++++++++++++++++-------------------
 1 file changed, 33 insertions(+), 27 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index a43039d..686951a 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1706,6 +1706,38 @@ static void pl011_shutdown(struct uart_port *port)
 }
 
 static void
+pl011_setup_status_masks(struct uart_port *port, struct ktermios *termios)
+{
+	port->read_status_mask = UART011_DR_OE | 255;
+	if (termios->c_iflag & INPCK)
+		port->read_status_mask |= UART011_DR_FE | UART011_DR_PE;
+	if (termios->c_iflag & (IGNBRK | BRKINT | PARMRK))
+		port->read_status_mask |= UART011_DR_BE;
+
+	/*
+	 * Characters to ignore
+	 */
+	port->ignore_status_mask = 0;
+	if (termios->c_iflag & IGNPAR)
+		port->ignore_status_mask |= UART011_DR_FE | UART011_DR_PE;
+	if (termios->c_iflag & IGNBRK) {
+		port->ignore_status_mask |= UART011_DR_BE;
+		/*
+		 * If we're ignoring parity and break indicators,
+		 * ignore overruns too (for real raw support).
+		 */
+		if (termios->c_iflag & IGNPAR)
+			port->ignore_status_mask |= UART011_DR_OE;
+	}
+
+	/*
+	 * Ignore all characters if CREAD is not set.
+	 */
+	if ((termios->c_cflag & CREAD) == 0)
+		port->ignore_status_mask |= UART_DUMMY_DR_RX;
+}
+
+static void
 pl011_set_termios(struct uart_port *port, struct ktermios *termios,
 		     struct ktermios *old)
 {
@@ -1769,33 +1801,7 @@ pl011_set_termios(struct uart_port *port, struct ktermios *termios,
 	 */
 	uart_update_timeout(port, termios->c_cflag, baud);
 
-	port->read_status_mask = UART011_DR_OE | 255;
-	if (termios->c_iflag & INPCK)
-		port->read_status_mask |= UART011_DR_FE | UART011_DR_PE;
-	if (termios->c_iflag & (IGNBRK | BRKINT | PARMRK))
-		port->read_status_mask |= UART011_DR_BE;
-
-	/*
-	 * Characters to ignore
-	 */
-	port->ignore_status_mask = 0;
-	if (termios->c_iflag & IGNPAR)
-		port->ignore_status_mask |= UART011_DR_FE | UART011_DR_PE;
-	if (termios->c_iflag & IGNBRK) {
-		port->ignore_status_mask |= UART011_DR_BE;
-		/*
-		 * If we're ignoring parity and break indicators,
-		 * ignore overruns too (for real raw support).
-		 */
-		if (termios->c_iflag & IGNPAR)
-			port->ignore_status_mask |= UART011_DR_OE;
-	}
-
-	/*
-	 * Ignore all characters if CREAD is not set.
-	 */
-	if ((termios->c_cflag & CREAD) == 0)
-		port->ignore_status_mask |= UART_DUMMY_DR_RX;
+	pl011_setup_status_masks(port, termios);
 
 	if (UART_ENABLE_MS(port, termios->c_cflag))
 		pl011_enable_ms(port);
-- 
2.3.5

[PATCH v5 05/11] drivers: PL011: refactor pl011_probe()

[Andre Przywara]

Currently the pl011_probe() function is relying on some AMBA IDs
and a device tree node to initialize the driver and a port.
Both features are not necessarily required for the driver:
- we lack AMBA IDs in the ARM SBSA generic UART and
- we lack a DT node in ACPI systems.
So lets refactor the function to ease later reuse.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/tty/serial/amba-pl011.c | 96 ++++++++++++++++++++++++++---------------
 1 file changed, 61 insertions(+), 35 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 686951a..38d2245 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -2173,65 +2173,54 @@ static void pl011_unregister_port(struct uart_amba_port *uap)
 		uart_unregister_driver(&amba_reg);
 }
 
-static int pl011_probe(struct amba_device *dev, const struct amba_id *id)
+static int pl011_find_free_port(void)
 {
-	struct uart_amba_port *uap;
-	struct vendor_data *vendor = id->data;
-	void __iomem *base;
-	int i, ret;
+	int i;
 
 	for (i = 0; i < ARRAY_SIZE(amba_ports); i++)
 		if (amba_ports[i] == NULL)
-			break;
-
-	if (i == ARRAY_SIZE(amba_ports))
-		return -EBUSY;
+			return i;
 
-	uap = devm_kzalloc(&dev->dev, sizeof(struct uart_amba_port),
-			   GFP_KERNEL);
-	if (uap == NULL)
-		return -ENOMEM;
+	return -EBUSY;
+}
 
-	i = pl011_probe_dt_alias(i, &dev->dev);
+static int pl011_setup_port(struct device *dev, struct uart_amba_port *uap,
+			    struct resource *mmiobase, int index)
+{
+	void __iomem *base;
 
-	base = devm_ioremap(&dev->dev, dev->res.start,
-			    resource_size(&dev->res));
+	base = devm_ioremap_resource(dev, mmiobase);
 	if (!base)
 		return -ENOMEM;
 
-	uap->clk = devm_clk_get(&dev->dev, NULL);
-	if (IS_ERR(uap->clk))
-		return PTR_ERR(uap->clk);
+	index = pl011_probe_dt_alias(index, dev);
 
-	uap->vendor = vendor;
-	uap->lcrh_rx = vendor->lcrh_rx;
-	uap->lcrh_tx = vendor->lcrh_tx;
 	uap->old_cr = 0;
-	uap->fifosize = vendor->get_fifosize(dev);
-	uap->port.dev = &dev->dev;
-	uap->port.mapbase = dev->res.start;
+	uap->port.dev = dev;
+	uap->port.mapbase = mmiobase->start;
 	uap->port.membase = base;
 	uap->port.iotype = UPIO_MEM;
-	uap->port.irq = dev->irq[0];
 	uap->port.fifosize = uap->fifosize;
-	uap->port.ops = &amba_pl011_pops;
 	uap->port.flags = UPF_BOOT_AUTOCONF;
-	uap->port.line = i;
+	uap->port.line = index;
 
-	/* Ensure interrupts from this UART are masked and cleared */
-	writew(0, uap->port.membase + UART011_IMSC);
-	writew(0xffff, uap->port.membase + UART011_ICR);
+	amba_ports[index] = uap;
 
-	snprintf(uap->type, sizeof(uap->type), "PL011 rev%u", amba_rev(dev));
+	return 0;
+}
 
-	amba_ports[i] = uap;
+static int pl011_register_port(struct uart_amba_port *uap)
+{
+	int ret;
 
-	amba_set_drvdata(dev, uap);
+	/* Ensure interrupts from this UART are masked and cleared */
+	writew(0, uap->port.membase + UART011_IMSC);
+	writew(0xffff, uap->port.membase + UART011_ICR);
 
 	if (!amba_reg.state) {
 		ret = uart_register_driver(&amba_reg);
 		if (ret < 0) {
-			dev_err(&dev->dev,
+			dev_err(uap->port.dev,
 				"Failed to register AMBA-PL011 driver\n");
 			return ret;
 		}
@@ -2244,6 +2233,43 @@ static int pl011_probe(struct amba_device *dev, const struct amba_id *id)
 	return ret;
 }
 
+static int pl011_probe(struct amba_device *dev, const struct amba_id *id)
+{
+	struct uart_amba_port *uap;
+	struct vendor_data *vendor = id->data;
+	int portnr, ret;
+
+	portnr = pl011_find_free_port();
+	if (portnr < 0)
+		return portnr;
+
+	uap = devm_kzalloc(&dev->dev, sizeof(struct uart_amba_port),
+			   GFP_KERNEL);
+	if (!uap)
+		return -ENOMEM;
+
+	uap->clk = devm_clk_get(&dev->dev, NULL);
+	if (IS_ERR(uap->clk))
+		return PTR_ERR(uap->clk);
+
+	uap->vendor = vendor;
+	uap->lcrh_rx = vendor->lcrh_rx;
+	uap->lcrh_tx = vendor->lcrh_tx;
+	uap->fifosize = vendor->get_fifosize(dev);
+	uap->port.irq = dev->irq[0];
+	uap->port.ops = &amba_pl011_pops;
+
+	snprintf(uap->type, sizeof(uap->type), "PL011 rev%u", amba_rev(dev));
+
+	ret = pl011_setup_port(&dev->dev, uap, &dev->res, portnr);
+	if (ret)
+		return ret;
+
+	amba_set_drvdata(dev, uap);
+
+	return pl011_register_port(uap);
+}
+
 static int pl011_remove(struct amba_device *dev)
 {
 	struct uart_amba_port *uap = amba_get_drvdata(dev);
-- 
2.3.5

Re: [PATCH v5 05/11] drivers: PL011: refactor pl011_probe()

[Timur Tabi]

On Thu, May 21, 2015 at 9:26 AM, Andre Przywara <andre.przywara@arm.com> wrote:
> +static int pl011_probe(struct amba_device *dev, const struct amba_id *id)
> +{
> +       struct uart_amba_port *uap;
> +       struct vendor_data *vendor = id->data;
> +       int portnr, ret;
> +
> +       portnr = pl011_find_free_port();
> +       if (portnr < 0)
> +               return portnr;
> +
> +       uap = devm_kzalloc(&dev->dev, sizeof(struct uart_amba_port),
> +                          GFP_KERNEL);
> +       if (!uap)
> +               return -ENOMEM;
> +
> +       uap->clk = devm_clk_get(&dev->dev, NULL);
> +       if (IS_ERR(uap->clk))
> +               return PTR_ERR(uap->clk);
> +
> +       = vendor;

I'm having trouble with this.  Specifically, I can't get SBSA early
console to work, because uap->vendor is uninitialized when
pl011_early_write() is called.

I don't have a non-SBSA system to test, but looking at the code, I'm
not sure how early console is supposed to work any more.  In both SBSA
and non-SBSA cases, uap->vendor is not initialized until the probe
function is called.  Isn't that too late?  I thought early console was
supposed to be running before the driver is probed.

If I make this change, then early console works on SBSA systems (with
earlycon=pl011,<address>).  But of course, this only works for SBSA
and breaks regular PL011.

--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -2326,9 +2326,15 @@ static void pl011_early_write(struct console *con, const
 static int __init pl011_early_console_setup(struct earlycon_device *device,
                                            const char *opt)
 {
+       struct uart_amba_port *uap =
+           container_of(&device->port, struct uart_amba_port, port);
+
        if (!device->port.membase)
                return -ENODEV;
+       if (!uap->vendor)
+               uap->vendor = &vendor_sbsa;
+
        device->con->write = pl011_early_write;
        return 0;
 }

-- 
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project.

Re: [PATCH v5 05/11] drivers: PL011: refactor pl011_probe()

[Andre Przywara]

Hi Timur,

(sorry for the delay, just found your email which arrived during my
vacation)

On 09/08/15 01:59, Timur Tabi wrote:
> On Thu, May 21, 2015 at 9:26 AM, Andre Przywara <andre.przywara@arm.com> wrote:
>> +static int pl011_probe(struct amba_device *dev, const struct amba_id *id)
>> +{
>> +       struct uart_amba_port *uap;
>> +       struct vendor_data *vendor = id->data;
>> +       int portnr, ret;
>> +
>> +       portnr = pl011_find_free_port();
>> +       if (portnr < 0)
>> +               return portnr;
>> +
>> +       uap = devm_kzalloc(&dev->dev, sizeof(struct uart_amba_port),
>> +                          GFP_KERNEL);
>> +       if (!uap)
>> +               return -ENOMEM;
>> +
>> +       uap->clk = devm_clk_get(&dev->dev, NULL);
>> +       if (IS_ERR(uap->clk))
>> +               return PTR_ERR(uap->clk);
>> +
>> +       = vendor;
> 
> I'm having trouble with this.  Specifically, I can't get SBSA early
> console to work, because uap->vendor is uninitialized when
> pl011_early_write() is called.

I don't get where pl011_early_write() would need any kind of PL011 struct.
It only references structures defined in the serial core, so it's
completely dumb MMIO writes and reads, using only the base address
provided on the command line.
Are you by any chance mixing up early console and the normal console? To
me it looks like early console just uses the three tiny functions
defined just before the declaration and it does not touch vendor at all,
isn't it?

As for the broken part, any chance you were testing -next, which has
some patches that broke early console, as we learned today?[1]

Cheers,
Andre.
[1]:
http://lists.infradead.org/pipermail/linux-arm-kernel/2015-September/367744.html

> 
> I don't have a non-SBSA system to test, but looking at the code, I'm
> not sure how early console is supposed to work any more.  In both SBSA
> and non-SBSA cases, uap->vendor is not initialized until the probe
> function is called.  Isn't that too late?  I thought early console was
> supposed to be running before the driver is probed.
> 
> If I make this change, then early console works on SBSA systems (with
> earlycon=pl011,<address>).  But of course, this only works for SBSA
> and breaks regular PL011.
> 
> --- a/drivers/tty/serial/amba-pl011.c
> +++ b/drivers/tty/serial/amba-pl011.c
> @@ -2326,9 +2326,15 @@ static void pl011_early_write(struct console *con, const
>  static int __init pl011_early_console_setup(struct earlycon_device *device,
>                                             const char *opt)
>  {
> +       struct uart_amba_port *uap =
> +           container_of(&device->port, struct uart_amba_port, port);
> +
>         if (!device->port.membase)
>                 return -ENODEV;
> +       if (!uap->vendor)
> +               uap->vendor = &vendor_sbsa;
> +
>         device->con->write = pl011_early_write;
>         return 0;
>  }
> 

Re: [PATCH v5 05/11] drivers: PL011: refactor pl011_probe()

[Timur Tabi]

On 09/03/2015 11:54 AM, Andre Przywara wrote:

> I don't get where pl011_early_write() would need any kind of PL011 struct.
> It only references structures defined in the serial core, so it's
> completely dumb MMIO writes and reads, using only the base address
> provided on the command line.
> Are you by any chance mixing up early console and the normal console? To
> me it looks like early console just uses the three tiny functions
> defined just before the declaration and it does not touch vendor at all,
> isn't it?
>
> As for the broken part, any chance you were testing -next, which has
> some patches that broke early console, as we learned today?[1]

I have to apologize -- I forgot that I applied an internal patch that 
modified this code, and the bug is in that patch, not yours.  Your code 
is fine as is.

[PATCH v5 06/11] drivers: PL011: replace UART_MIS reading with _RIS & _IMSC

[Andre Przywara]

The PL011 register UART_MIS is actually a bitwise AND of the
UART_RIS and the UART_MISC register.
Since the SBSA UART does not include the _MIS register, use the
two separate registers to get the same behaviour. Since we are
inside the spinlock and we read the _IMSC register only once, there
should be no race issue.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/tty/serial/amba-pl011.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 38d2245..b66636b 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1322,11 +1322,13 @@ static irqreturn_t pl011_int(int irq, void *dev_id)
 	struct uart_amba_port *uap = dev_id;
 	unsigned long flags;
 	unsigned int status, pass_counter = AMBA_ISR_PASS_LIMIT;
+	u16 imsc;
 	int handled = 0;
 	unsigned int dummy_read;
 
 	spin_lock_irqsave(&uap->port.lock, flags);
-	status = readw(uap->port.membase + UART011_MIS);
+	imsc = readw(uap->port.membase + UART011_IMSC);
+	status = readw(uap->port.membase + UART011_RIS) & imsc;
 	if (status) {
 		do {
 			if (uap->vendor->cts_event_workaround) {
@@ -1361,7 +1363,7 @@ static irqreturn_t pl011_int(int irq, void *dev_id)
 			if (pass_counter-- == 0)
 				break;
 
-			status = readw(uap->port.membase + UART011_MIS);
+			status = readw(uap->port.membase + UART011_RIS) & imsc;
 		} while (status != 0);
 		handled = 1;
 	}
-- 
2.3.5

[PATCH v5 07/11] drivers: PL011: move cts_event workaround into separate function

[Andre Przywara]

To avoid lines with more than 80 characters and to make the
pl011_int() function more readable, move the workaround out into a
separate function.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/tty/serial/amba-pl011.c | 33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index b66636b..7ecf3b3 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -1317,6 +1317,25 @@ static void pl011_modem_status(struct uart_amba_port *uap)
 	wake_up_interruptible(&uap->port.state->port.delta_msr_wait);
 }
 
+static void check_apply_cts_event_workaround(struct uart_amba_port *uap)
+{
+	unsigned int dummy_read;
+
+	if (!uap->vendor->cts_event_workaround)
+		return;
+
+	/* workaround to make sure that all bits are unlocked.. */
+	writew(0x00, uap->port.membase + UART011_ICR);
+
+	/*
+	 * WA: introduce 26ns(1 uart clk) delay before W1C;
+	 * single apb access will incur 2 pclk(133.12Mhz) delay,
+	 * so add 2 dummy reads
+	 */
+	dummy_read = readw(uap->port.membase + UART011_ICR);
+	dummy_read = readw(uap->port.membase + UART011_ICR);
+}
+
 static irqreturn_t pl011_int(int irq, void *dev_id)
 {
 	struct uart_amba_port *uap = dev_id;
@@ -1324,25 +1343,13 @@ static irqreturn_t pl011_int(int irq, void *dev_id)
 	unsigned int status, pass_counter = AMBA_ISR_PASS_LIMIT;
 	u16 imsc;
 	int handled = 0;
-	unsigned int dummy_read;
 
 	spin_lock_irqsave(&uap->port.lock, flags);
 	imsc = readw(uap->port.membase + UART011_IMSC);
 	status = readw(uap->port.membase + UART011_RIS) & imsc;
 	if (status) {
 		do {
-			if (uap->vendor->cts_event_workaround) {
-				/* workaround to make sure that all bits are unlocked.. */
-				writew(0x00, uap->port.membase + UART011_ICR);
-
-				/*
-				 * WA: introduce 26ns(1 uart clk) delay before W1C;
-				 * single apb access will incur 2 pclk(133.12Mhz) delay,
-				 * so add 2 dummy reads
-				 */
-				dummy_read = readw(uap->port.membase + UART011_ICR);
-				dummy_read = readw(uap->port.membase + UART011_ICR);
-			}
+			check_apply_cts_event_workaround(uap);
 
 			writew(status & ~(UART011_TXIS|UART011_RTIS|
 					  UART011_RXIS),
-- 
2.3.5

[PATCH v5 08/11] drivers: PL011: allow avoiding UART enabling/disabling

[Andre Przywara]

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>
---
 drivers/tty/serial/amba-pl011.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 7ecf3b3..3f6b915 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/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);
-- 
2.3.5

[PATCH v5 09/11] drivers: PL011: allow to supply fixed option string

[Andre Przywara]

The SBSA UART has a fixed baud rate and flow control setting, which
cannot be changed or queried by software.
Add a vendor specific property to always return fixed values when
trying to read the console options.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/tty/serial/amba-pl011.c | 17 +++++++++++++----
 1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 3f6b915..6558400 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -79,6 +79,7 @@ struct vendor_data {
 	bool			dma_threshold;
 	bool			cts_event_workaround;
 	bool			always_enabled;
+	bool			fixed_options;
 
 	unsigned int (*get_fifosize)(struct amba_device *dev);
 };
@@ -96,6 +97,7 @@ static struct vendor_data vendor_arm = {
 	.dma_threshold		= false,
 	.cts_event_workaround	= false,
 	.always_enabled		= false,
+	.fixed_options		= false,
 	.get_fifosize		= get_fifosize_arm,
 };
 
@@ -112,6 +114,7 @@ static struct vendor_data vendor_st = {
 	.dma_threshold		= true,
 	.cts_event_workaround	= true,
 	.always_enabled		= false,
+	.fixed_options		= false,
 	.get_fifosize		= get_fifosize_st,
 };
 
@@ -160,6 +163,7 @@ struct uart_amba_port {
 	unsigned int		lcrh_rx;	/* vendor-specific */
 	unsigned int		old_cr;		/* state during shutdown */
 	bool			autorts;
+	unsigned int		fixed_baud;	/* vendor-set fixed baud rate */
 	char			type[12];
 #ifdef CONFIG_DMA_ENGINE
 	/* DMA stuff */
@@ -2076,10 +2080,15 @@ static int __init pl011_console_setup(struct console *co, char *options)
 
 	uap->port.uartclk = clk_get_rate(uap->clk);
 
-	if (options)
-		uart_parse_options(options, &baud, &parity, &bits, &flow);
-	else
-		pl011_console_get_options(uap, &baud, &parity, &bits);
+	if (uap->vendor->fixed_options) {
+		baud = uap->fixed_baud;
+	} else {
+		if (options)
+			uart_parse_options(options,
+					   &baud, &parity, &bits, &flow);
+		else
+			pl011_console_get_options(uap, &baud, &parity, &bits);
+	}
 
 	return uart_set_options(&uap->port, co, baud, parity, bits, flow);
 }
-- 
2.3.5

[PATCH v5 10/11] drivers: PL011: add support for the ARM SBSA generic UART

[Andre Przywara]

The ARM Server Base System Architecture[1] document describes a
generic UART which is a subset of the PL011 UART.
It lacks DMA support, baud rate control and modem status line
control, among other things.
The idea is to move the UART initialization and setup into the
firmware (which does this job today already) and let the kernel just
use the UART for sending and receiving characters.

We use the recent refactoring to build a new struct uart_ops
variable which points to some new functions avoiding access to the
missing registers. We reuse as much existing PL011 code as possible.

In contrast to the PL011 the SBSA UART does not define any AMBA or
PrimeCell relations, so we go with a pretty generic probe function
which only uses platform device functions.
A DT binding is provided with this patch, ACPI support is added in a
separate one.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 .../devicetree/bindings/serial/arm_sbsa_uart.txt   |  10 ++
 drivers/tty/serial/amba-pl011.c                    | 171 +++++++++++++++++++++
 2 files changed, 181 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/serial/arm_sbsa_uart.txt

diff --git a/Documentation/devicetree/bindings/serial/arm_sbsa_uart.txt b/Documentation/devicetree/bindings/serial/arm_sbsa_uart.txt
new file mode 100644
index 0000000..4163e7e
--- /dev/null
+++ b/Documentation/devicetree/bindings/serial/arm_sbsa_uart.txt
@@ -0,0 +1,10 @@
+* ARM SBSA defined generic UART
+This UART uses a subset of the PL011 registers and consequently lives
+in the PL011 driver. It's baudrate and other communication parameters
+cannot be adjusted at runtime, so it lacks a clock specifier here.
+
+Required properties:
+- compatible: must be "arm,sbsa-uart"
+- reg: exactly one register range
+- interrupts: exactly one interrupt specifier
+- current-speed: the (fixed) baud rate set by the firmware
diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index 6558400..c0850f3 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -101,6 +101,14 @@ static struct vendor_data vendor_arm = {
 	.get_fifosize		= get_fifosize_arm,
 };
 
+static struct vendor_data vendor_sbsa = {
+	.oversampling		= false,
+	.dma_threshold		= false,
+	.cts_event_workaround	= false,
+	.always_enabled		= true,
+	.fixed_options		= true,
+};
+
 static unsigned int get_fifosize_st(struct amba_device *dev)
 {
 	return 64;
@@ -1641,6 +1649,28 @@ static int pl011_startup(struct uart_port *port)
 	return retval;
 }
 
+static int sbsa_uart_startup(struct uart_port *port)
+{
+	struct uart_amba_port *uap =
+		container_of(port, struct uart_amba_port, port);
+	int retval;
+
+	retval = pl011_hwinit(port);
+	if (retval)
+		return retval;
+
+	retval = pl011_allocate_irq(uap);
+	if (retval)
+		return retval;
+
+	/* The SBSA UART does not support any modem status lines. */
+	uap->old_status = 0;
+
+	pl011_enable_interrupts(uap);
+
+	return 0;
+}
+
 static void pl011_shutdown_channel(struct uart_amba_port *uap,
 					unsigned int lcrh)
 {
@@ -1721,6 +1751,19 @@ static void pl011_shutdown(struct uart_port *port)
 		uap->port.ops->flush_buffer(port);
 }
 
+static void sbsa_uart_shutdown(struct uart_port *port)
+{
+	struct uart_amba_port *uap =
+		container_of(port, struct uart_amba_port, port);
+
+	pl011_disable_interrupts(uap);
+
+	free_irq(uap->port.irq, uap);
+
+	if (uap->port.ops->flush_buffer)
+		uap->port.ops->flush_buffer(port);
+}
+
 static void
 pl011_setup_status_masks(struct uart_port *port, struct ktermios *termios)
 {
@@ -1872,6 +1915,27 @@ pl011_set_termios(struct uart_port *port, struct ktermios *termios,
 	spin_unlock_irqrestore(&port->lock, flags);
 }
 
+static void
+sbsa_uart_set_termios(struct uart_port *port, struct ktermios *termios,
+		      struct ktermios *old)
+{
+	struct uart_amba_port *uap =
+	    container_of(port, struct uart_amba_port, port);
+	unsigned long flags;
+
+	tty_termios_encode_baud_rate(termios, uap->fixed_baud, uap->fixed_baud);
+
+	/* The SBSA UART only supports 8n1 without hardware flow control. */
+	termios->c_cflag &= ~(CSIZE | CSTOPB | PARENB | PARODD);
+	termios->c_cflag &= ~(CMSPAR | CRTSCTS);
+	termios->c_cflag |= CS8 | CLOCAL;
+
+	spin_lock_irqsave(&port->lock, flags);
+	uart_update_timeout(port, CS8, uap->fixed_baud);
+	pl011_setup_status_masks(port, termios);
+	spin_unlock_irqrestore(&port->lock, flags);
+}
+
 static const char *pl011_type(struct uart_port *port)
 {
 	struct uart_amba_port *uap =
@@ -1947,6 +2011,37 @@ static struct uart_ops amba_pl011_pops = {
 #endif
 };
 
+static void sbsa_uart_set_mctrl(struct uart_port *port, unsigned int mctrl)
+{
+}
+
+static unsigned int sbsa_uart_get_mctrl(struct uart_port *port)
+{
+	return 0;
+}
+
+static const struct uart_ops sbsa_uart_pops = {
+	.tx_empty	= pl011_tx_empty,
+	.set_mctrl	= sbsa_uart_set_mctrl,
+	.get_mctrl	= sbsa_uart_get_mctrl,
+	.stop_tx	= pl011_stop_tx,
+	.start_tx	= pl011_start_tx,
+	.stop_rx	= pl011_stop_rx,
+	.startup	= sbsa_uart_startup,
+	.shutdown	= sbsa_uart_shutdown,
+	.set_termios	= sbsa_uart_set_termios,
+	.type		= pl011_type,
+	.release_port	= pl011_release_port,
+	.request_port	= pl011_request_port,
+	.config_port	= pl011_config_port,
+	.verify_port	= pl011_verify_port,
+#ifdef CONFIG_CONSOLE_POLL
+	.poll_init     = pl011_hwinit,
+	.poll_get_char = pl011_get_poll_char,
+	.poll_put_char = pl011_put_poll_char,
+#endif
+};
+
 static struct uart_amba_port *amba_ports[UART_NR];
 
 #ifdef CONFIG_SERIAL_AMBA_PL011_CONSOLE
@@ -2327,6 +2422,79 @@ static int pl011_resume(struct device *dev)
 
 static SIMPLE_DEV_PM_OPS(pl011_dev_pm_ops, pl011_suspend, pl011_resume);
 
+static int sbsa_uart_probe(struct platform_device *pdev)
+{
+	struct uart_amba_port *uap;
+	struct resource *r;
+	int portnr, ret;
+	int baudrate;
+
+	/*
+	 * Check the mandatory baud rate parameter in the DT node early
+	 * so that we can easily exit with the error.
+	 */
+	if (pdev->dev.of_node) {
+		struct device_node *np = pdev->dev.of_node;
+
+		ret = of_property_read_u32(np, "current-speed", &baudrate);
+		if (ret)
+			return ret;
+	} else {
+		baudrate = 115200;
+	}
+
+	portnr = pl011_find_free_port();
+	if (portnr < 0)
+		return portnr;
+
+	uap = devm_kzalloc(&pdev->dev, sizeof(struct uart_amba_port),
+			   GFP_KERNEL);
+	if (!uap)
+		return -ENOMEM;
+
+	uap->vendor	= &vendor_sbsa;
+	uap->fifosize	= 32;
+	uap->port.irq	= platform_get_irq(pdev, 0);
+	uap->port.ops	= &sbsa_uart_pops;
+	uap->fixed_baud = baudrate;
+
+	snprintf(uap->type, sizeof(uap->type), "SBSA");
+
+	r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+
+	ret = pl011_setup_port(&pdev->dev, uap, r, portnr);
+	if (ret)
+		return ret;
+
+	platform_set_drvdata(pdev, uap);
+
+	return pl011_register_port(uap);
+}
+
+static int sbsa_uart_remove(struct platform_device *pdev)
+{
+	struct uart_amba_port *uap = platform_get_drvdata(pdev);
+
+	uart_remove_one_port(&amba_reg, &uap->port);
+	pl011_unregister_port(uap);
+	return 0;
+}
+
+static const struct of_device_id sbsa_uart_of_match[] = {
+	{ .compatible = "arm,sbsa-uart", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, sbsa_uart_of_match);
+
+static struct platform_driver arm_sbsa_uart_platform_driver = {
+	.probe		= sbsa_uart_probe,
+	.remove		= sbsa_uart_remove,
+	.driver	= {
+		.name	= "sbsa-uart",
+		.of_match_table = of_match_ptr(sbsa_uart_of_match),
+	},
+};
+
 static struct amba_id pl011_ids[] = {
 	{
 		.id	= 0x00041011,
@@ -2357,11 +2525,14 @@ static int __init pl011_init(void)
 {
 	printk(KERN_INFO "Serial: AMBA PL011 UART driver\n");
 
+	if (platform_driver_register(&arm_sbsa_uart_platform_driver))
+		pr_warn("could not register SBSA UART platform driver\n");
 	return amba_driver_register(&pl011_driver);
 }
 
 static void __exit pl011_exit(void)
 {
+	platform_driver_unregister(&arm_sbsa_uart_platform_driver);
 	amba_driver_unregister(&pl011_driver);
 }
 
-- 
2.3.5

[PATCH v5 11/11] drivers: PL011: add ACPI probing for SBSA UART

[Andre Przywara]

From: Graeme Gregory <graeme.gregory@linaro.org>

Add the necessary driver boilerplate to let the driver be used when
the respective ACPI table is discovered by the ACPI subsystem.

[Andre: change table name, add MODULE_DEVICE_TABLE entry and improve
	commit message]

Reviewed-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Graeme Gregory <graeme.gregory@linaro.org>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 drivers/tty/serial/amba-pl011.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
index c0850f3..50cf5b1 100644
--- a/drivers/tty/serial/amba-pl011.c
+++ b/drivers/tty/serial/amba-pl011.c
@@ -58,6 +58,7 @@
 #include <linux/pinctrl/consumer.h>
 #include <linux/sizes.h>
 #include <linux/io.h>
+#include <linux/acpi.h>
 
 #define UART_NR			14
 
@@ -2486,12 +2487,19 @@ static const struct of_device_id sbsa_uart_of_match[] = {
 };
 MODULE_DEVICE_TABLE(of, sbsa_uart_of_match);
 
+static const struct acpi_device_id sbsa_uart_acpi_match[] = {
+	{ "ARMH0011", 0 },
+	{},
+};
+MODULE_DEVICE_TABLE(acpi, sbsa_uart_acpi_match);
+
 static struct platform_driver arm_sbsa_uart_platform_driver = {
 	.probe		= sbsa_uart_probe,
 	.remove		= sbsa_uart_remove,
 	.driver	= {
 		.name	= "sbsa-uart",
 		.of_match_table = of_match_ptr(sbsa_uart_of_match),
+		.acpi_match_table = ACPI_PTR(sbsa_uart_acpi_match),
 	},
 };
 
-- 
2.3.5

Re: [PATCH v5 00/11] drivers: PL011: add ARM SBSA Generic UART support

[Mark Langsdorf]

On 05/21/2015 11:26 AM, Andre Przywara wrote:
> This is the fifth revision of the SBSA UART support series, based on
> the current tty-next branch.
> Beside some minor formatting issues fixed (thanks ot Jakub for
> noticing) the SBSA UART set_termios() function has been reworked.
> We now completely ignore the old value, instead we filter the new
> setting to match the SBSA UART's fixed parameters for word size,
> parity, stop bits and so on.
> This should also address the issues people have seen with ACPI on
> Fedora systems.
> Mark, Naresh, Graeme: can you confirm that this version works for
> you? If needed I can bake a follow-up patch on top of v4.
> ----

Works for me, thanks.

Tested-by: Mark Langsdorf <mlangsdo@redhat.com>

--Mark Langsdorf

> The ARM Server Base System Architecture[1] document describes a
> generic UART which is a subset of the ARM PL011 UART.
> It lacks DMA support, baud rate control and modem status line
> control, among other things.
> The idea is to move the UART initialization and setup into the
> firmware (which does this job today already) and let the kernel just
> use the UART for sending and receiving characters.
>
> This patchset integrates support for this UART subset into the
> existing PL011 driver - basically by refactoring some
> functions and providing a new uart_ops structure for it. It also has
> a separate probe function to be not dependent on AMBA/PrimeCell.
> It provides a device tree and an ACPI binding.
> Beside the obvious effect of code sharing reusing most of the PL011
> code has the advantage of not introducing another serial device
> prefix, so it can go with ttyAMA, which seems to be pretty common.
> As changing the baudrate and other communication parameters is not
> specified for the SBSA UART, any userland attempt will be denied by
> the kernel. The device-tree provided fixed baud rate will be
> reported, so stty for instance prints the right value.
>
> This series is based on Greg's tty-next branch, a git repo can
> be found at [2] (branch sbsa-uart/v5).
>
> Patch 1/11 contains a bug fix which applies to the PL011 part also,
> it should be considered regardless of the rest of the series.
> According to Russell this is still racy, but still better than the
> current solution.
> Patch 2-7 refactor some PL011 functions by splitting them up into
> smaller pieces, so that most of the code can be reused later by the
> SBSA part.
> Patch 8 and 9 introduce two new properties for the vendor structure,
> this is for SBSA functionality which cannot be controlled by
> separate uart_ops members only.
> Patch 10 then finally drops in the SBSA specific code, by providing
> a new uart_ops, vendor struct and probe function for it. Also the new
> device tree binding is documented.
> Patch 11 adds the necessary ACPI boilerplate.
>
> For testing you should be able to take any hardware which has a PL011
> and change the DT to use a "arm,sbsa-uart" compatible string and the
> baud rate with the "current-speed" property.
> Of course testing with a real SBSA Generic UART is welcomed - as well
> as regression testing with any PL011 implementation.
> I tested this on a FastModel, a Juno and a Midway machine, both in
> PL011 and in (DT-emulated) SBSA mode.
>
> Tested-by: Robert Richter <rrichter@cavium.com>
> Tested-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Tested-by: Hanjun Guo <hanjun.guo@linaro.org>
>
> Changelog:
> v4 .. v5:
> - fixed checkpatch --strict complaints
> - rework set_termios:
>    - disallow changes or UART fixed communication parameters
>    - ignore old value to fix an issue with Fedora on ACPI
>
> v3 .. v4:
> - fixed rebase artifact
> - moved memory allocation out of pl011_allocate_port() function
>    (and consequently renamed that to pl011_find_free_port)
> - added ACPI driver binding
>
> v2 .. v3:
> - rebased on top of tty-next and Dave's latest PL011 rework
> - fixed module build
> - removed redundant =NULL members in sbsa_uart_ops
>
> v1 .. v2:
> - rebased on top of 4.0-rc1 and Dave's newest PL011 fix [3]
> - added mandatory current-speed property and report that to userland
>
> Cheers,
> Andre
>
> [1] ARM-DEN-0029 Server Base System Architecture, available (click-
>      thru...) from http://infocenter.arm.com
> [2] http://www.linux-arm.org/git?p=linux-ap.git
>      git://linux-arm.org/linux-ap.git
> [3] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-March/327631.html
>
> Andre Przywara (10):
>    drivers: PL011: avoid potential unregister_driver call
>    drivers: PL011: refactor pl011_startup()
>    drivers: PL011: refactor pl011_shutdown()
>    drivers: PL011: refactor pl011_set_termios()
>    drivers: PL011: refactor pl011_probe()
>    drivers: PL011: replace UART_MIS reading with _RIS & _IMSC
>    drivers: PL011: move cts_event workaround into separate function
>    drivers: PL011: allow avoiding UART enabling/disabling
>    drivers: PL011: allow to supply fixed option string
>    drivers: PL011: add support for the ARM SBSA generic UART
>
> Graeme Gregory (1):
>    drivers: PL011: add ACPI probing for SBSA UART
>
>   .../devicetree/bindings/serial/arm_sbsa_uart.txt   |  10 +
>   drivers/tty/serial/amba-pl011.c                    | 550 +++++++++++++++------
>   2 files changed, 412 insertions(+), 148 deletions(-)
>   create mode 100644 Documentation/devicetree/bindings/serial/arm_sbsa_uart.txt
>

Re: [PATCH v5 00/11] drivers: PL011: add ARM SBSA Generic UART support

[Graeme Gregory]

On 21 May 2015 18:19:18 BST, Mark Langsdorf <mlangsdo@redhat.com> wrote:
>On 05/21/2015 11:26 AM, Andre Przywara wrote:
>> This is the fifth revision of the SBSA UART support series, based on
>> the current tty-next branch.
>> Beside some minor formatting issues fixed (thanks ot Jakub for
>> noticing) the SBSA UART set_termios() function has been reworked.
>> We now completely ignore the old value, instead we filter the new
>> setting to match the SBSA UART's fixed parameters for word size,
>> parity, stop bits and so on.
>> This should also address the issues people have seen with ACPI on
>> Fedora systems.
>> Mark, Naresh, Graeme: can you confirm that this version works for
>> you? If needed I can bake a follow-up patch on top of v4.
>> ----
>
>Works for me, thanks.
>
>Tested-by: Mark Langsdorf <mlangsdo@redhat.com>
>
>--Mark Langsdorf
>
I am on holiday so can't retest but Mark is using same setup as me so please proceed

Graeme

>> The ARM Server Base System Architecture[1] document describes a
>> generic UART which is a subset of the ARM PL011 UART.
>> It lacks DMA support, baud rate control and modem status line
>> control, among other things.
>> The idea is to move the UART initialization and setup into the
>> firmware (which does this job today already) and let the kernel just
>> use the UART for sending and receiving characters.
>>
>> This patchset integrates support for this UART subset into the
>> existing PL011 driver - basically by refactoring some
>> functions and providing a new uart_ops structure for it. It also has
>> a separate probe function to be not dependent on AMBA/PrimeCell.
>> It provides a device tree and an ACPI binding.
>> Beside the obvious effect of code sharing reusing most of the PL011
>> code has the advantage of not introducing another serial device
>> prefix, so it can go with ttyAMA, which seems to be pretty common.
>> As changing the baudrate and other communication parameters is not
>> specified for the SBSA UART, any userland attempt will be denied by
>> the kernel. The device-tree provided fixed baud rate will be
>> reported, so stty for instance prints the right value.
>>
>> This series is based on Greg's tty-next branch, a git repo can
>> be found at [2] (branch sbsa-uart/v5).
>>
>> Patch 1/11 contains a bug fix which applies to the PL011 part also,
>> it should be considered regardless of the rest of the series.
>> According to Russell this is still racy, but still better than the
>> current solution.
>> Patch 2-7 refactor some PL011 functions by splitting them up into
>> smaller pieces, so that most of the code can be reused later by the
>> SBSA part.
>> Patch 8 and 9 introduce two new properties for the vendor structure,
>> this is for SBSA functionality which cannot be controlled by
>> separate uart_ops members only.
>> Patch 10 then finally drops in the SBSA specific code, by providing
>> a new uart_ops, vendor struct and probe function for it. Also the new
>> device tree binding is documented.
>> Patch 11 adds the necessary ACPI boilerplate.
>>
>> For testing you should be able to take any hardware which has a PL011
>> and change the DT to use a "arm,sbsa-uart" compatible string and the
>> baud rate with the "current-speed" property.
>> Of course testing with a real SBSA Generic UART is welcomed - as well
>> as regression testing with any PL011 implementation.
>> I tested this on a FastModel, a Juno and a Midway machine, both in
>> PL011 and in (DT-emulated) SBSA mode.
>>
>> Tested-by: Robert Richter <rrichter@cavium.com>
>> Tested-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
>> Tested-by: Hanjun Guo <hanjun.guo@linaro.org>
>>
>> Changelog:
>> v4 .. v5:
>> - fixed checkpatch --strict complaints
>> - rework set_termios:
>>    - disallow changes or UART fixed communication parameters
>>    - ignore old value to fix an issue with Fedora on ACPI
>>
>> v3 .. v4:
>> - fixed rebase artifact
>> - moved memory allocation out of pl011_allocate_port() function
>>    (and consequently renamed that to pl011_find_free_port)
>> - added ACPI driver binding
>>
>> v2 .. v3:
>> - rebased on top of tty-next and Dave's latest PL011 rework
>> - fixed module build
>> - removed redundant =NULL members in sbsa_uart_ops
>>
>> v1 .. v2:
>> - rebased on top of 4.0-rc1 and Dave's newest PL011 fix [3]
>> - added mandatory current-speed property and report that to userland
>>
>> Cheers,
>> Andre
>>
>> [1] ARM-DEN-0029 Server Base System Architecture, available (click-
>>      thru...) from http://infocenter.arm.com
>> [2] http://www.linux-arm.org/git?p=linux-ap.git
>>      git://linux-arm.org/linux-ap.git
>> [3]
>http://lists.infradead.org/pipermail/linux-arm-kernel/2015-March/327631.html
>>
>> Andre Przywara (10):
>>    drivers: PL011: avoid potential unregister_driver call
>>    drivers: PL011: refactor pl011_startup()
>>    drivers: PL011: refactor pl011_shutdown()
>>    drivers: PL011: refactor pl011_set_termios()
>>    drivers: PL011: refactor pl011_probe()
>>    drivers: PL011: replace UART_MIS reading with _RIS & _IMSC
>>    drivers: PL011: move cts_event workaround into separate function
>>    drivers: PL011: allow avoiding UART enabling/disabling
>>    drivers: PL011: allow to supply fixed option string
>>    drivers: PL011: add support for the ARM SBSA generic UART
>>
>> Graeme Gregory (1):
>>    drivers: PL011: add ACPI probing for SBSA UART
>>
>>   .../devicetree/bindings/serial/arm_sbsa_uart.txt   |  10 +
>>   drivers/tty/serial/amba-pl011.c                    | 550
>+++++++++++++++------
>>   2 files changed, 412 insertions(+), 148 deletions(-)
>>   create mode 100644
>Documentation/devicetree/bindings/serial/arm_sbsa_uart.txt
>>

-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.

Re: [PATCH v5 00/11] drivers: PL011: add ARM SBSA Generic UART support

[Naresh Bhat]

Hi Andre Przywara,

On Thu, May 21, 2015 at 9:56 PM, Andre Przywara <andre.przywara@arm.com> wrote:
> This is the fifth revision of the SBSA UART support series, based on
> the current tty-next branch.
> Beside some minor formatting issues fixed (thanks ot Jakub for
> noticing) the SBSA UART set_termios() function has been reworked.
> We now completely ignore the old value, instead we filter the new
> setting to match the SBSA UART's fixed parameters for word size,
> parity, stop bits and so on.
> This should also address the issues people have seen with ACPI on
> Fedora systems.
> Mark, Naresh, Graeme: can you confirm that this version works for
> you? If needed I can bake a follow-up patch on top of v4.

Thanks.

Yes, I have tested this series on Cavium ThunderX with Fedora21 FS
works fine for me.

Tested-by: Naresh Bhat <nbhat@cavium.com>

> ----
>
> The ARM Server Base System Architecture[1] document describes a
> generic UART which is a subset of the ARM PL011 UART.
> It lacks DMA support, baud rate control and modem status line
> control, among other things.
> The idea is to move the UART initialization and setup into the
> firmware (which does this job today already) and let the kernel just
> use the UART for sending and receiving characters.
>
> This patchset integrates support for this UART subset into the
> existing PL011 driver - basically by refactoring some
> functions and providing a new uart_ops structure for it. It also has
> a separate probe function to be not dependent on AMBA/PrimeCell.
> It provides a device tree and an ACPI binding.
> Beside the obvious effect of code sharing reusing most of the PL011
> code has the advantage of not introducing another serial device
> prefix, so it can go with ttyAMA, which seems to be pretty common.
> As changing the baudrate and other communication parameters is not
> specified for the SBSA UART, any userland attempt will be denied by
> the kernel. The device-tree provided fixed baud rate will be
> reported, so stty for instance prints the right value.
>
> This series is based on Greg's tty-next branch, a git repo can
> be found at [2] (branch sbsa-uart/v5).
>
> Patch 1/11 contains a bug fix which applies to the PL011 part also,
> it should be considered regardless of the rest of the series.
> According to Russell this is still racy, but still better than the
> current solution.
> Patch 2-7 refactor some PL011 functions by splitting them up into
> smaller pieces, so that most of the code can be reused later by the
> SBSA part.
> Patch 8 and 9 introduce two new properties for the vendor structure,
> this is for SBSA functionality which cannot be controlled by
> separate uart_ops members only.
> Patch 10 then finally drops in the SBSA specific code, by providing
> a new uart_ops, vendor struct and probe function for it. Also the new
> device tree binding is documented.
> Patch 11 adds the necessary ACPI boilerplate.
>
> For testing you should be able to take any hardware which has a PL011
> and change the DT to use a "arm,sbsa-uart" compatible string and the
> baud rate with the "current-speed" property.
> Of course testing with a real SBSA Generic UART is welcomed - as well
> as regression testing with any PL011 implementation.
> I tested this on a FastModel, a Juno and a Midway machine, both in
> PL011 and in (DT-emulated) SBSA mode.
>
> Tested-by: Robert Richter <rrichter@cavium.com>
> Tested-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Tested-by: Hanjun Guo <hanjun.guo@linaro.org>
>
> Changelog:
> v4 .. v5:
> - fixed checkpatch --strict complaints
> - rework set_termios:
>   - disallow changes or UART fixed communication parameters
>   - ignore old value to fix an issue with Fedora on ACPI
>
> v3 .. v4:
> - fixed rebase artifact
> - moved memory allocation out of pl011_allocate_port() function
>   (and consequently renamed that to pl011_find_free_port)
> - added ACPI driver binding
>
> v2 .. v3:
> - rebased on top of tty-next and Dave's latest PL011 rework
> - fixed module build
> - removed redundant =NULL members in sbsa_uart_ops
>
> v1 .. v2:
> - rebased on top of 4.0-rc1 and Dave's newest PL011 fix [3]
> - added mandatory current-speed property and report that to userland
>
> Cheers,
> Andre
>
> [1] ARM-DEN-0029 Server Base System Architecture, available (click-
>     thru...) from http://infocenter.arm.com
> [2] http://www.linux-arm.org/git?p=linux-ap.git
>     git://linux-arm.org/linux-ap.git
> [3] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-March/327631.html
>
> Andre Przywara (10):
>   drivers: PL011: avoid potential unregister_driver call
>   drivers: PL011: refactor pl011_startup()
>   drivers: PL011: refactor pl011_shutdown()
>   drivers: PL011: refactor pl011_set_termios()
>   drivers: PL011: refactor pl011_probe()
>   drivers: PL011: replace UART_MIS reading with _RIS & _IMSC
>   drivers: PL011: move cts_event workaround into separate function
>   drivers: PL011: allow avoiding UART enabling/disabling
>   drivers: PL011: allow to supply fixed option string
>   drivers: PL011: add support for the ARM SBSA generic UART
>
> Graeme Gregory (1):
>   drivers: PL011: add ACPI probing for SBSA UART
>
>  .../devicetree/bindings/serial/arm_sbsa_uart.txt   |  10 +
>  drivers/tty/serial/amba-pl011.c                    | 550 +++++++++++++++------
>  2 files changed, 412 insertions(+), 148 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/serial/arm_sbsa_uart.txt
>
> --
> 2.3.5
>



-- 
"For things to change, we must change"
-Naresh Bhat