[PATCH] serdev: BREAK/FRAME/PARITY/OVERRUN notification prototype V2

[PATCH] serdev: BREAK/FRAME/PARITY/OVERRUN notification prototype V2

[Magnus Damm]

From: Magnus Damm <damm+renesas@opensource.se>

Allow serdev device drivers get notified by hardware errors such as BREAK,
FRAME, PARITY and OVERRUN.

With this patch, in the event of an error detected in the UART device driver
the serdev_device_driver will get the newly introduced ->error() callback
invoked if serdev_device_set_error_mask() has previously been used to enable
the type of error. The errors are taken straight from the TTY layer and fed
into the serdev_device_driver after filtering out only enabled errors.

Without this patch the hardware errors never reach the serdev_device_driver.

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
---

 Applies to linux-5.16-rc4

 Change since V1:
 - Use __set_bit() instead of set_bit() in ttyport_receive_buf()
 - Switch to assign_bit() in ttyport_set_error_mask()

 Thanks to Geert for feedback!

 The following prototype patch is using serdev error notifications:
 [PATCH] r8a77995 Draak SCIF0 LED and KEY Serdev prototype V2

 drivers/tty/serdev/core.c           |   11 +++++++
 drivers/tty/serdev/serdev-ttyport.c |   49 +++++++++++++++++++++++++++++++++++
 include/linux/serdev.h              |   22 +++++++++++++++
 3 files changed, 82 insertions(+)

--- 0001/drivers/tty/serdev/core.c
+++ work/drivers/tty/serdev/core.c	2021-12-12 21:36:51.756818597 +0900
@@ -349,6 +349,17 @@ unsigned int serdev_device_set_baudrate(
 }
 EXPORT_SYMBOL_GPL(serdev_device_set_baudrate);
 
+void serdev_device_set_error_mask(struct serdev_device *serdev, unsigned long mask)
+{
+	struct serdev_controller *ctrl = serdev->ctrl;
+
+	if (!ctrl || !ctrl->ops->set_error_mask)
+		return;
+
+	ctrl->ops->set_error_mask(ctrl, mask);
+}
+EXPORT_SYMBOL_GPL(serdev_device_set_error_mask);
+
 void serdev_device_set_flow_control(struct serdev_device *serdev, bool enable)
 {
 	struct serdev_controller *ctrl = serdev->ctrl;
--- 0001/drivers/tty/serdev/serdev-ttyport.c
+++ work/drivers/tty/serdev/serdev-ttyport.c	2021-12-12 21:53:42.698882261 +0900
@@ -2,6 +2,7 @@
 /*
  * Copyright (C) 2016-2017 Linaro Ltd., Rob Herring <robh@kernel.org>
  */
+#include <linux/bits.h>
 #include <linux/kernel.h>
 #include <linux/serdev.h>
 #include <linux/tty.h>
@@ -9,6 +10,10 @@
 #include <linux/poll.h>
 
 #define SERPORT_ACTIVE		1
+#define SERPORT_NOTIFY_BREAK	2
+#define SERPORT_NOTIFY_FRAME	3
+#define SERPORT_NOTIFY_PARITY	4
+#define SERPORT_NOTIFY_OVERRUN	5
 
 struct serport {
 	struct tty_port *port;
@@ -27,11 +32,39 @@ static int ttyport_receive_buf(struct tt
 {
 	struct serdev_controller *ctrl = port->client_data;
 	struct serport *serport = serdev_controller_get_drvdata(ctrl);
+	unsigned long errors = 0;
+	unsigned int i;
 	int ret;
 
 	if (!test_bit(SERPORT_ACTIVE, &serport->flags))
 		return 0;
 
+	for (i = 0; fp && i < count; i++) {
+		switch (fp[i]) {
+		case TTY_BREAK:
+			if (test_bit(SERPORT_NOTIFY_BREAK, &serport->flags))
+				__set_bit(SERDEV_ERROR_BREAK, &errors);
+			break;
+
+		case TTY_FRAME:
+			if (test_bit(SERPORT_NOTIFY_FRAME, &serport->flags))
+				__set_bit(SERDEV_ERROR_FRAME, &errors);
+			break;
+
+		case TTY_PARITY:
+			if (test_bit(SERPORT_NOTIFY_PARITY, &serport->flags))
+				__set_bit(SERDEV_ERROR_PARITY, &errors);
+			break;
+
+		case TTY_OVERRUN:
+			if (test_bit(SERPORT_NOTIFY_OVERRUN, &serport->flags))
+				__set_bit(SERDEV_ERROR_OVERRUN, &errors);
+			break;
+		}
+	}
+	if (errors)
+		serdev_controller_error(ctrl, errors);
+
 	ret = serdev_controller_receive_buf(ctrl, cp, count);
 
 	dev_WARN_ONCE(&ctrl->dev, ret < 0 || ret > count,
@@ -180,6 +213,21 @@ static unsigned int ttyport_set_baudrate
 	return ktermios.c_ospeed;
 }
 
+static void ttyport_set_error_mask(struct serdev_controller *ctrl,
+				   unsigned long m)
+{
+	struct serport *sp = serdev_controller_get_drvdata(ctrl);
+
+	assign_bit(SERPORT_NOTIFY_BREAK, &sp->flags,
+		   m & BIT(SERDEV_ERROR_BREAK));
+	assign_bit(SERPORT_NOTIFY_FRAME, &sp->flags,
+		   m & BIT(SERDEV_ERROR_FRAME));
+	assign_bit(SERPORT_NOTIFY_PARITY, &sp->flags,
+		   m & BIT(SERDEV_ERROR_PARITY));
+	assign_bit(SERPORT_NOTIFY_OVERRUN, &sp->flags,
+		   m & BIT(SERDEV_ERROR_OVERRUN));
+}
+
 static void ttyport_set_flow_control(struct serdev_controller *ctrl, bool enable)
 {
 	struct serport *serport = serdev_controller_get_drvdata(ctrl);
@@ -253,6 +301,7 @@ static const struct serdev_controller_op
 	.write_room = ttyport_write_room,
 	.open = ttyport_open,
 	.close = ttyport_close,
+	.set_error_mask = ttyport_set_error_mask,
 	.set_flow_control = ttyport_set_flow_control,
 	.set_parity = ttyport_set_parity,
 	.set_baudrate = ttyport_set_baudrate,
--- 0001/include/linux/serdev.h
+++ work/include/linux/serdev.h	2021-12-12 21:36:51.757818597 +0900
@@ -19,12 +19,15 @@ struct serdev_device;
 
 /**
  * struct serdev_device_ops - Callback operations for a serdev device
+ * @error:		Function called with errors received from device;
+ *			may sleep.
  * @receive_buf:	Function called with data received from device;
  *			returns number of bytes accepted; may sleep.
  * @write_wakeup:	Function called when ready to transmit more data; must
  *			not sleep.
  */
 struct serdev_device_ops {
+	void (*error)(struct serdev_device *, unsigned long);
 	int (*receive_buf)(struct serdev_device *, const unsigned char *, size_t);
 	void (*write_wakeup)(struct serdev_device *);
 };
@@ -76,6 +79,11 @@ enum serdev_parity {
 	SERDEV_PARITY_ODD,
 };
 
+#define SERDEV_ERROR_BREAK 0
+#define SERDEV_ERROR_FRAME 1
+#define SERDEV_ERROR_PARITY 2
+#define SERDEV_ERROR_OVERRUN 3
+
 /*
  * serdev controller structures
  */
@@ -85,6 +93,7 @@ struct serdev_controller_ops {
 	int (*write_room)(struct serdev_controller *);
 	int (*open)(struct serdev_controller *);
 	void (*close)(struct serdev_controller *);
+	void (*set_error_mask)(struct serdev_controller *, unsigned long);
 	void (*set_flow_control)(struct serdev_controller *, bool);
 	int (*set_parity)(struct serdev_controller *, enum serdev_parity);
 	unsigned int (*set_baudrate)(struct serdev_controller *, unsigned int);
@@ -190,12 +199,24 @@ static inline int serdev_controller_rece
 	return serdev->ops->receive_buf(serdev, data, count);
 }
 
+static inline void serdev_controller_error(struct serdev_controller *ctrl,
+					   unsigned long errors)
+{
+	struct serdev_device *serdev = ctrl->serdev;
+
+	if (!serdev || !serdev->ops->error)
+		return;
+
+	serdev->ops->error(serdev, errors);
+}
+
 #if IS_ENABLED(CONFIG_SERIAL_DEV_BUS)
 
 int serdev_device_open(struct serdev_device *);
 void serdev_device_close(struct serdev_device *);
 int devm_serdev_device_open(struct device *, struct serdev_device *);
 unsigned int serdev_device_set_baudrate(struct serdev_device *, unsigned int);
+void serdev_device_set_error_mask(struct serdev_device *, unsigned long);
 void serdev_device_set_flow_control(struct serdev_device *, bool);
 int serdev_device_write_buf(struct serdev_device *, const unsigned char *, size_t);
 void serdev_device_wait_until_sent(struct serdev_device *, long);
@@ -238,6 +259,7 @@ static inline unsigned int serdev_device
 {
 	return 0;
 }
+static inline void serdev_device_set_error_mask(struct serdev_device *sdev, unsigned long mask) {}
 static inline void serdev_device_set_flow_control(struct serdev_device *sdev, bool enable) {}
 static inline int serdev_device_write_buf(struct serdev_device *serdev,
 					  const unsigned char *buf,

Re: [PATCH] serdev: BREAK/FRAME/PARITY/OVERRUN notification prototype V2

[Greg KH]

On Sun, Dec 12, 2021 at 10:21:28PM +0900, Magnus Damm wrote:
> From: Magnus Damm <damm+renesas@opensource.se>
> 
> Allow serdev device drivers get notified by hardware errors such as BREAK,
> FRAME, PARITY and OVERRUN.
> 
> With this patch, in the event of an error detected in the UART device driver
> the serdev_device_driver will get the newly introduced ->error() callback
> invoked if serdev_device_set_error_mask() has previously been used to enable
> the type of error. The errors are taken straight from the TTY layer and fed
> into the serdev_device_driver after filtering out only enabled errors.
> 
> Without this patch the hardware errors never reach the serdev_device_driver.
> 
> Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
> ---
> 
>  Applies to linux-5.16-rc4
> 
>  Change since V1:
>  - Use __set_bit() instead of set_bit() in ttyport_receive_buf()
>  - Switch to assign_bit() in ttyport_set_error_mask()
> 
>  Thanks to Geert for feedback!
> 
>  The following prototype patch is using serdev error notifications:
>  [PATCH] r8a77995 Draak SCIF0 LED and KEY Serdev prototype V2

Looks good, now applied to my tty tree.

thanks,

greg k-h

Re: [PATCH] serdev: BREAK/FRAME/PARITY/OVERRUN notification prototype V2

[Johan Hovold]

On Thu, Dec 30, 2021 at 01:30:18PM +0100, Greg Kroah-Hartman wrote:
> On Sun, Dec 12, 2021 at 10:21:28PM +0900, Magnus Damm wrote:
> > From: Magnus Damm <damm+renesas@opensource.se>
> > 
> > Allow serdev device drivers get notified by hardware errors such as BREAK,
> > FRAME, PARITY and OVERRUN.
> > 
> > With this patch, in the event of an error detected in the UART device driver
> > the serdev_device_driver will get the newly introduced ->error() callback
> > invoked if serdev_device_set_error_mask() has previously been used to enable
> > the type of error. The errors are taken straight from the TTY layer and fed
> > into the serdev_device_driver after filtering out only enabled errors.
> > 
> > Without this patch the hardware errors never reach the serdev_device_driver.
> > 
> > Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
> > ---
> > 
> >  Applies to linux-5.16-rc4
> > 
> >  Change since V1:
> >  - Use __set_bit() instead of set_bit() in ttyport_receive_buf()
> >  - Switch to assign_bit() in ttyport_set_error_mask()
> > 
> >  Thanks to Geert for feedback!
> > 
> >  The following prototype patch is using serdev error notifications:
> >  [PATCH] r8a77995 Draak SCIF0 LED and KEY Serdev prototype V2
> 
> Looks good, now applied to my tty tree.

I really don't think this is ready to be merged. There's been no
discussion about the design of this interface and importantly there are
no users (there was an RFC floating around but that one too has issues).

Some of the problems with this patch include:

 - performance penalty for all serdev drivers due to unconditional per
   character processing
 - flagged characters are still being forwarded to the consumer (e.g.
   NUL chars inserted on breaks)
 - it only works with some broken serial drivers which do not honour
   TTY_DRIVER_REAL_RAW
 - interface basically limited to the hacky led/input driver mentioned
   above since it does not match flags with characters

I suggest reverting for now.

Johan

Re: [PATCH] serdev: BREAK/FRAME/PARITY/OVERRUN notification prototype V2

[Greg KH]

On Fri, Dec 31, 2021 at 12:24:23PM +0100, Johan Hovold wrote:
> On Thu, Dec 30, 2021 at 01:30:18PM +0100, Greg Kroah-Hartman wrote:
> > On Sun, Dec 12, 2021 at 10:21:28PM +0900, Magnus Damm wrote:
> > > From: Magnus Damm <damm+renesas@opensource.se>
> > > 
> > > Allow serdev device drivers get notified by hardware errors such as BREAK,
> > > FRAME, PARITY and OVERRUN.
> > > 
> > > With this patch, in the event of an error detected in the UART device driver
> > > the serdev_device_driver will get the newly introduced ->error() callback
> > > invoked if serdev_device_set_error_mask() has previously been used to enable
> > > the type of error. The errors are taken straight from the TTY layer and fed
> > > into the serdev_device_driver after filtering out only enabled errors.
> > > 
> > > Without this patch the hardware errors never reach the serdev_device_driver.
> > > 
> > > Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
> > > ---
> > > 
> > >  Applies to linux-5.16-rc4
> > > 
> > >  Change since V1:
> > >  - Use __set_bit() instead of set_bit() in ttyport_receive_buf()
> > >  - Switch to assign_bit() in ttyport_set_error_mask()
> > > 
> > >  Thanks to Geert for feedback!
> > > 
> > >  The following prototype patch is using serdev error notifications:
> > >  [PATCH] r8a77995 Draak SCIF0 LED and KEY Serdev prototype V2
> > 
> > Looks good, now applied to my tty tree.
> 
> I really don't think this is ready to be merged. There's been no
> discussion about the design of this interface and importantly there are
> no users (there was an RFC floating around but that one too has issues).
> 
> Some of the problems with this patch include:
> 
>  - performance penalty for all serdev drivers due to unconditional per
>    character processing
>  - flagged characters are still being forwarded to the consumer (e.g.
>    NUL chars inserted on breaks)
>  - it only works with some broken serial drivers which do not honour
>    TTY_DRIVER_REAL_RAW
>  - interface basically limited to the hacky led/input driver mentioned
>    above since it does not match flags with characters
> 
> I suggest reverting for now.

No problem, will go revert it right now, thanks for looking at it.

greg k-h