tty: serial: msm_serial: Use DT aliases

From: Frank Rowand <[email protected]>

Update devicetree binding for msm_serial to reflect msm_serial_probe() getting line id from the serial alias.

Signed-off-by Frank Rowand <[email protected]>

---
 Documentation/devicetree/bindings/serial/qcom,msm-uartdm.txt |   15 +++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

Index: b/Documentation/devicetree/bindings/serial/qcom,msm-uartdm.txt
===================================================================

From: Frank Rowand <[email protected]>

v2, changes from v1:
- The patch this documents was updated to make the serialN alias optional instead of required.

Update devicetree binding for msm_serial to reflect msm_serial_probe() getting line id from the serial alias.

Signed-off-by Frank Rowand <[email protected]>

From: Frank Rowand <[email protected]>

Update msm8974 dtsi for msm_serial to reflect msm_serial_probe() getting line id from the serial alias.

Signed-off-by Frank Rowand <[email protected]>

---
 arch/arm/boot/dts/qcom-msm8974.dtsi |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

Index: b/arch/arm/boot/dts/qcom-msm8974.dtsi
===================================================================

arch/arm/boot/dts/qcom-msm8974.dtsi +4 -0

@@ -9,6 +9,10 @@
 	compatible = "qcom,msm8974";
 	interrupt-parent = <&intc>;
 
+	aliases {
+		serial0 = &serial0;
+	};
+
 	cpus {
 		#address-cells = <1>;
 		#size-cells = <0>;

This same change is also needed in:

qcom-ipq8064.dtsi
qcom-msm8960.dtsi
qcom-apq8084.dtsi
qcom-apq8064.dtsi
qcom-msm8660.dtsi

but I did not want to just blindly apply those changes without testing.

Quoted 8 lines · On Thursday 06 November 2014 22:42:47 Frank Rowand wrote:

This same change is also needed in:

qcom-ipq8064.dtsi
qcom-msm8960.dtsi
qcom-apq8084.dtsi
qcom-apq8064.dtsi
qcom-msm8660.dtsi

Quoted 2 lines

but I did not want to just blindly apply those changes without testing.

Is there only one uart on each of these?

If not, it would be better to put the aliases in the board specific file, pointing to whichever ports are in use, in the order that makes sense for that board.

Quoted 9 lines · Arnd Bergmann

Quoted 8 lines · On Thursday 06 November 2014 22:42:47 Frank Rowand wrote:

This same change is also needed in:

qcom-ipq8064.dtsi
qcom-msm8960.dtsi
qcom-apq8084.dtsi
qcom-apq8064.dtsi
qcom-msm8660.dtsi

Quoted 8 lines

Quoted 2 lines

but I did not want to just blindly apply those changes without testing.

Is there only one uart on each of these?

If not, it would be better to put the aliases in the board specific file, pointing to whichever ports are in use, in the order that makes sense for that board.

Good point, thanks for bringing it up.

Your comment made me verify that the board dts files can override the aliases from the included .dtsi. So not a problem to have a default set of aliases in the .dtsi files.

We rely on probe order of this driver to determine the line number for the uart port. This makes it impossible to know the line number when these devices are populated via DT. Use the DT alias mechanism to assign the line based on the aliases node.

Signed-off-by Stephen Boyd <[email protected]>

Quoted 5 lines · Stephen Boyd

We rely on probe order of this driver to determine the line number for the uart port. This makes it impossible to know the line number when these devices are populated via DT. Use the DT alias mechanism to assign the line based on the aliases node.

Quoted 1 line

Signed-off-by Stephen Boyd <[email protected]>

FYI... this patch hit linux-next and caused multiple boot failures on qcom platforms[1] as of next-20141110. I'm assuming this is because the corresponding DTS changes have not hit linux-next yet.

Kevin

[1] http://status.armcloud.us/boot/?qcom

Quoted 6 lines · Kevin Hilman

Quoted 5 lines · Stephen Boyd

We rely on probe order of this driver to determine the line number for the uart port. This makes it impossible to know the line number when these devices are populated via DT. Use the DT alias mechanism to assign the line based on the aliases node.

Quoted 8 lines

Quoted 1 line

Signed-off-by Stephen Boyd <[email protected]>

FYI... this patch hit linux-next and caused multiple boot failures on qcom platforms[1] as of next-20141110. I'm assuming this is because the corresponding DTS changes have not hit linux-next yet.

Kevin

[1] http://status.armcloud.us/boot/?qcom

Hmm the intention was to make it optional so that dts changes aren't necessary unless you want deterministic numbering. I screwed that up badly :/ Thanks for finding this.

Greg, can you also apply this patch or squash it into the bad one?

----8<-----

From: Stephen Boyd <[email protected]>
Subject: [PATCH] tty: serial: msm_serial: Don't required DT aliases

If there isn't a DT alias then of_alias_get_id() will return -ENODEV. This will cause the msm_serial driver to fail probe, when we want to keep the previous behavior where we generated a dynamic line number at probe time. Restore this behavior by generating a dynamic id if the line number is still negative after checking for an alias or (in the non-DT case) looking at the .id field of the platform device.

Reported-by Kevin Hilman <[email protected]>

Signed-off-by Stephen Boyd <[email protected]>

---
 drivers/tty/serial/msm_serial.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

drivers/tty/serial/msm_serial.c +0 -2

index 09364dd8cf3a..d1bc6b6cbc70 100644
@@ -1046,14 +1046,14 @@ static int msm_serial_probe(struct platform_device *pdev)
 	const struct of_device_id *id;
 	int irq, line;
 
-	if (pdev->id == -1)
-		pdev->id = atomic_inc_return(&msm_uart_next_id) - 1;

drivers/tty/serial/msm_serial.c +0 -0

 		return -ENXIO;
 

Quoted 16 lines · Stephen Boyd

drivers/tty/serial/msm_serial.c +0 -3

index 09364dd8cf3a..d1bc6b6cbc70 100644
@@ -1046,14 +1046,14 @@ static int msm_serial_probe(struct platform_device *pdev)
 	const struct of_device_id *id;
 	int irq, line;
 
-	if (pdev->id == -1)
-		pdev->id = atomic_inc_return(&msm_uart_next_id) - 1;
-
 	if (pdev->dev.of_node)
 		line = of_alias_get_id(pdev->dev.of_node, "serial");
 	else
 		line = pdev->id;
 

drivers/tty/serial/msm_serial.c static int msm_serial_probe(struct platform_device *pdev) · line 1057

Quoted 4 lines

drivers/tty/serial/msm_serial.c +3 -0

+	if (line < 0)
+		line = atomic_inc_return(&msm_uart_next_id) - 1;
+
 	if (unlikely(line < 0 || line >= UART_NR))

Then this original check for "line < 0" can also be removed.

Quoted 17 lines · Frank Rowand

Quoted 16 lines · Stephen Boyd

drivers/tty/serial/msm_serial.c +0 -3

index 09364dd8cf3a..d1bc6b6cbc70 100644
@@ -1046,14 +1046,14 @@ static int msm_serial_probe(struct platform_device *pdev)
 	const struct of_device_id *id;
 	int irq, line;
 
-	if (pdev->id == -1)
-		pdev->id = atomic_inc_return(&msm_uart_next_id) - 1;
-
 	if (pdev->dev.of_node)
 		line = of_alias_get_id(pdev->dev.of_node, "serial");
 	else
 		line = pdev->id;
 

Quoted 7 lines

drivers/tty/serial/msm_serial.c static int msm_serial_probe(struct platform_device *pdev) · line 1057

Quoted 4 lines

drivers/tty/serial/msm_serial.c +3 -0

+	if (line < 0)
+		line = atomic_inc_return(&msm_uart_next_id) - 1;
+
 	if (unlikely(line < 0 || line >= UART_NR))

Then this original check for "line < 0" can also be removed.

Well this matches what was there before. It would do atomic_inc_return if the line was negative and then still check for a negative value. I don't mind removing it though. Perhaps we should use an ida?:

Quoted 26 lines · Stephen Boyd

Quoted 17 lines · Frank Rowand

Quoted 16 lines · Stephen Boyd

drivers/tty/serial/msm_serial.c +0 -3

index 09364dd8cf3a..d1bc6b6cbc70 100644
@@ -1046,14 +1046,14 @@ static int msm_serial_probe(struct platform_device *pdev)
 	const struct of_device_id *id;
 	int irq, line;
 
-	if (pdev->id == -1)
-		pdev->id = atomic_inc_return(&msm_uart_next_id) - 1;
-
 	if (pdev->dev.of_node)
 		line = of_alias_get_id(pdev->dev.of_node, "serial");
 	else
 		line = pdev->id;
 

Quoted 7 lines

drivers/tty/serial/msm_serial.c static int msm_serial_probe(struct platform_device *pdev) · line 1057

Quoted 4 lines

drivers/tty/serial/msm_serial.c +3 -0

+	if (line < 0)
+		line = atomic_inc_return(&msm_uart_next_id) - 1;
+
 	if (unlikely(line < 0 || line >= UART_NR))

Then this original check for "line < 0" can also be removed.

Quoted 4 lines

Well this matches what was there before. It would do atomic_inc_return if the line was negative and then still check for a negative value. I don't mind removing it though. Perhaps we should use an ida?:

OK, you are right. If (pdev->id < -1) and (!pdev->dev.of_node) then the check is still needed.

You could use an ida. Some drivers use a bit map. I really don't think this should become a complicated algorithm though. If the rule is that either all UARTS have an alias, or no UART has an alias, then I think the patch could be something like the following.

This combines your original patch, plus your fix patch, plus making the aliases all or nothing. Not tested, not even compiled.

What do you think?

Quoted 38 lines · Frank Rowand

Quoted 25 lines · Stephen Boyd

Quoted 17 lines · Frank Rowand

Quoted 16 lines · Stephen Boyd

drivers/tty/serial/msm_serial.c +0 -3

index 09364dd8cf3a..d1bc6b6cbc70 100644
@@ -1046,14 +1046,14 @@ static int msm_serial_probe(struct platform_device *pdev)
 	const struct of_device_id *id;
 	int irq, line;
 
-	if (pdev->id == -1)
-		pdev->id = atomic_inc_return(&msm_uart_next_id) - 1;
-
 	if (pdev->dev.of_node)
 		line = of_alias_get_id(pdev->dev.of_node, "serial");
 	else
 		line = pdev->id;
 

Quoted 7 lines

drivers/tty/serial/msm_serial.c static int msm_serial_probe(struct platform_device *pdev) · line 1057

Quoted 4 lines

drivers/tty/serial/msm_serial.c +3 -0

+	if (line < 0)
+		line = atomic_inc_return(&msm_uart_next_id) - 1;
+
 	if (unlikely(line < 0 || line >= UART_NR))

Then this original check for "line < 0" can also be removed.

Quoted 4 lines

Well this matches what was there before. It would do atomic_inc_return if the line was negative and then still check for a negative value. I don't mind removing it though. Perhaps we should use an ida?:

OK, you are right. If (pdev->id < -1) and (!pdev->dev.of_node) then the check is still needed.

You could use an ida. Some drivers use a bit map. I really don't think this should become a complicated algorithm though. If the rule is that either all UARTS have an alias, or no UART has an alias, then I think the patch could be something like the following.

Quoted 4 lines

This combines your original patch, plus your fix patch, plus making the aliases all or nothing. Not tested, not even compiled.

What do you think?

< snip - previous version of patch >

Previous version of the patch did not protect against no alias, followed by alias.

From: Frank Rowand <[email protected]>

This patch is intended to show roughly what an implementation of an all or nothing policy for using serialN aliases would look like. It is intended simply to help determine whether this policy should be used.

Combines Stephen's first patch, Stephen's fix patch (to make the serialN alias optional), plus makes use of the serialN alias all or nothing (either all ports have an alias or none do).

This is not a correct implementation because the atomic_read(&msm_uart_next_id) does not protect against concurrency; instead a lock should be used.

Not tested, not even compiled.

Quoted 56 lines · Frank Rowand

Quoted 38 lines · Frank Rowand

Quoted 25 lines · Stephen Boyd

Quoted 17 lines · Frank Rowand

Quoted 16 lines · Stephen Boyd

drivers/tty/serial/msm_serial.c +0 -3

index 09364dd8cf3a..d1bc6b6cbc70 100644
@@ -1046,14 +1046,14 @@ static int msm_serial_probe(struct platform_device *pdev)
 	const struct of_device_id *id;
 	int irq, line;
 
-	if (pdev->id == -1)
-		pdev->id = atomic_inc_return(&msm_uart_next_id) - 1;
-
 	if (pdev->dev.of_node)
 		line = of_alias_get_id(pdev->dev.of_node, "serial");
 	else
 		line = pdev->id;
 

Quoted 7 lines

drivers/tty/serial/msm_serial.c static int msm_serial_probe(struct platform_device *pdev) · line 1057

Quoted 4 lines

drivers/tty/serial/msm_serial.c +3 -0

+	if (line < 0)
+		line = atomic_inc_return(&msm_uart_next_id) - 1;
+
 	if (unlikely(line < 0 || line >= UART_NR))

Then this original check for "line < 0" can also be removed.

Quoted 4 lines

Well this matches what was there before. It would do atomic_inc_return if the line was negative and then still check for a negative value. I don't mind removing it though. Perhaps we should use an ida?:

OK, you are right. If (pdev->id < -1) and (!pdev->dev.of_node) then the check is still needed.

You could use an ida. Some drivers use a bit map. I really don't think this should become a complicated algorithm though. If the rule is that either all UARTS have an alias, or no UART has an alias, then I think the patch could be something like the following.

Quoted 4 lines

This combines your original patch, plus your fix patch, plus making the aliases all or nothing. Not tested, not even compiled.

What do you think?

< snip - previous version of patch >

Previous version of the patch did not protect against no alias, followed by alias.

From: Frank Rowand <[email protected]>

This patch is intended to show roughly what an implementation of an all or nothing policy for using serialN aliases would look like. It is intended simply to help determine whether this policy should be used.

Quoted 8 lines

Combines Stephen's first patch, Stephen's fix patch (to make the serialN alias optional), plus makes use of the serialN alias all or nothing (either all ports have an alias or none do).

This is not a correct implementation because the atomic_read(&msm_uart_next_id) does not protect against concurrency; instead a lock should be used.

Not tested, not even compiled.

Sorry, I'm sort of lost. If there are serial aliases in the dts file, then we should alias all of the serial ports. If there aren't aliases then we're backwards compatible with the dts we have now and we'll do dynamic generation. Putting code into the driver to validate that this is true is not the job of the driver. If anything, it should validated when the dts file is created. If one day we screw up and have a dts file with such a bad configuration we'll have to work around it, but until that day comes I'd rather not think about it.

Quoted 8 lines · Stephen Boyd

Sorry, I'm sort of lost. If there are serial aliases in the dts file, then we should alias all of the serial ports. If there aren't aliases then we're backwards compatible with the dts we have now and we'll do dynamic generation. Putting code into the driver to validate that this is true is not the job of the driver. If anything, it should validated when the dts file is created. If one day we screw up and have a dts file with such a bad configuration we'll have to work around it, but until that day comes I'd rather not think about it.

Maybe I did not understand when you said "Perhaps we should use an ida". That sentence led me to think the driver should check for misconfiguration. The case I was trying to handle was if there was at least one serialN alias and at least one UART without an alias. For example, if there are three UARTs (serial_a, serial_b, serial_c, probed in that order) and one alias (serial0 = &serial_c;) then the result would be:

   serial_a  line 0 (from msm_uart_next_id)
   serial_b  line 1 (from msm_uart_next_id)
   serial_c  line 0 (from the alias)

Two UARTs probed with line == 0. This is an error.

Most of the serial drivers don't check for this type of bad configuration. Some drivers keep a bit map of which lines have been used. I'm not sure what they do in case of a conflict (I did not read to that level of detail).

I thought you were suggesting the driver check for the bad configuration, so I was proposing a somewhat simple way of forcing a boot error for the bad configuration.

Since you are not suggesting the driver check for the bad configuration, you can ignore my proposal. I agree that it is ok for the driver to expect the board dts to be correct. The problem should be detected by the dts author on first boot as part of normal bring up testing, and then corrected.

Quoted 30 lines · Frank Rowand

Quoted 8 lines · Stephen Boyd

Sorry, I'm sort of lost. If there are serial aliases in the dts file, then we should alias all of the serial ports. If there aren't aliases then we're backwards compatible with the dts we have now and we'll do dynamic generation. Putting code into the driver to validate that this is true is not the job of the driver. If anything, it should validated when the dts file is created. If one day we screw up and have a dts file with such a bad configuration we'll have to work around it, but until that day comes I'd rather not think about it.

Maybe I did not understand when you said "Perhaps we should use an ida". That sentence led me to think the driver should check for misconfiguration. The case I was trying to handle was if there was at least one serialN alias and at least one UART without an alias. For example, if there are three UARTs (serial_a, serial_b, serial_c, probed in that order) and one alias (serial0 = &serial_c;) then the result would be:

   serial_a  line 0 (from msm_uart_next_id)
   serial_b  line 1 (from msm_uart_next_id)
   serial_c  line 0 (from the alias)

Two UARTs probed with line == 0. This is an error.

Most of the serial drivers don't check for this type of bad configuration. Some drivers keep a bit map of which lines have been used. I'm not sure what they do in case of a conflict (I did not read to that level of detail).

I thought you were suggesting the driver check for the bad configuration, so I was proposing a somewhat simple way of forcing a boot error for the bad configuration.

Quoted 6 lines

Since you are not suggesting the driver check for the bad configuration, you can ignore my proposal. I agree that it is ok for the driver to expect the board dts to be correct. The problem should be detected by the dts author on first boot as part of normal bring up testing, and then corrected.

Ah ok. I was just saying we could use an ida instead of an atomic increment so that this driver works properly with driver binding/unbinding, otherwise the line number keeps increasing and quickly goes beyond the static array of ports (which I still don't understand why we have at all btw).

Due to the length of the thread, I haven't followed all the details, and I suspect Greg hasn't either, so I'm not sure if you're discssuing what the right fix is for what's in -next (still broken[1], or what should be done with the device board files.

If the fix from earlier in this thread is still the right one for fixing -next, could you repost it separately for Greg to queue/squash and for me to re-test (if needed.)

Quoted 6 lines · Kevin Hilman

Quoted 5 lines · Stephen Boyd

We rely on probe order of this driver to determine the line number for the uart port. This makes it impossible to know the line number when these devices are populated via DT. Use the DT alias mechanism to assign the line based on the aliases node.

Quoted 8 lines

Quoted 1 line

Signed-off-by Stephen Boyd <[email protected]>

FYI... this patch hit linux-next and caused multiple boot failures on qcom platforms[1] as of next-20141110. I'm assuming this is because the corresponding DTS changes have not hit linux-next yet.

Kevin

[1] http://status.armcloud.us/boot/?qcom

Hmm the intention was to make it optional so that dts changes aren't necessary unless you want deterministic numbering. I screwed that up badly :/ Thanks for finding this.

Greg, can you also apply this patch or squash it into the bad one?

----8<-----

From: Stephen Boyd <[email protected]>
Subject: [PATCH] tty: serial: msm_serial: Don't required DT aliases

If there isn't a DT alias then of_alias_get_id() will return -ENODEV. This will cause the msm_serial driver to fail probe, when we want to keep the previous behavior where we generated a dynamic line number at probe time. Restore this behavior by generating a dynamic id if the line number is still negative after checking for an alias or (in the non-DT case) looking at the .id field of the platform device.

Reported-by Kevin Hilman <[email protected]>

Signed-off-by Stephen Boyd <[email protected]>