usb: typec: ucsi: Update UCSI alternate mode

Hi Heikki,

This series appliess some changes to the UCSI driver to help support AP driven alternate mode entry. This includes...

1. An update to the altmode sysfs group after registration to make "active" writable.
2. A change to the ucsi_partner_task delay when queuing ucsi_check_altmodes to prevent it from running before other discovery functions.
3. An update to always define a number of alternate modes for partners and plugs.

Not related to AP driven altmode entry, there is an additional fix for a null derefrence in this series.

I tested the series on a ChromeOS v6.8 kernel merged with usb-testing. That build had some additinal patches to enable a PPM in ChromeOS. Let me know if you have any questions.

Thanks,
Jameson

Changes in V2:
- Checks for error response from ucsi_register_displayport when registering DisplayPort alternate mode.

Abhishek Pandit-Subedi (2):
usb: typec: ucsi: Fix null deref in trace
usb: typec: Update sysfs when setting ops

Jameson Thies (2):
usb: typec: ucsi: Delay alternate mode discovery
usb: typec: ucsi: Always set number of alternate modes

 drivers/usb/typec/altmodes/displayport.c |  2 +-
 drivers/usb/typec/class.c                | 18 +++++++++++++++++-
 drivers/usb/typec/ucsi/displayport.c     |  2 +-
 drivers/usb/typec/ucsi/ucsi.c            | 21 ++++++++++++++++-----
 drivers/usb/typec/ucsi/ucsi.h            |  2 +-
 include/linux/usb/typec.h                |  3 +++
 6 files changed, 39 insertions(+), 9 deletions(-)

base-commit: 0d31ea587709216d88183fe4ca0c8aba5e0205b8

2.44.0.769.g3c40516874-goog

From: Abhishek Pandit-Subedi <[email protected]>

ucsi_register_altmode checks IS_ERR on returned pointer and treats NULL as valid. This results in a null deref when trace_ucsi_register_altmode is called. Return an error from ucsi_register_displayport when it is not supported and register the altmode with typec_port_register_altmode.

---
Changes in V2:
- Checks for error response from ucsi_register_displayport when registering DisplayPort alternate mode.

 drivers/usb/typec/ucsi/ucsi.c | 3 +++
 drivers/usb/typec/ucsi/ucsi.h | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)

index cb52e7b0a2c5c..f3b413f94fd28 100644
@@ -361,6 +361,9 @@ static int ucsi_register_altmode(struct ucsi_connector *con,
 		switch (desc->svid) {
 		case USB_TYPEC_DP_SID:
 			alt = ucsi_register_displayport(con, override, i, desc);
+			if (IS_ERR(alt) && PTR_ERR(alt) == -EOPNOTSUPP)
+				alt = typec_port_register_altmode(con->port, desc);
+
 			break;
 		case USB_TYPEC_NVIDIA_VLINK_SID:
 			if (desc->vdo == USB_TYPEC_NVIDIA_VLINK_DBG_VDO)

index c4d103db9d0f8..c663dce0659ee 100644
@@ -496,7 +496,7 @@ ucsi_register_displayport(struct ucsi_connector *con,
 			  bool override, int offset,
 			  struct typec_altmode_desc *desc)
 {
-	return NULL;
+	return ERR_PTR(-EOPNOTSUPP);
 }
 
 static inline void

2.44.0.769.g3c40516874-goog

So originally on my system, I didn't have the displayport driver config enabled. My expectation was that the alt-mode would show up but would not be controllable (like all other alt-modes without drivers). What ends up happening is that no alt-mode shows up and trying to enable the trace crashes.

When the displayport support isn't there, I think it should just be enumerated as a normal, unsupported alt-mode.

Hi,

This sounds reasonable. Thus if displayport support is not compiled in ucsi_register_displayport() should just call typec_port_register_altmode(), I guess.

Best regards,
Christian

…

…

Can it be nicer to use the term “null pointer dereference” for the commit message here?

Regards,
Markus

Hi,

This is the semi-friendly patch-bot of Greg Kroah-Hartman.

Markus, you seem to have sent a nonsensical or otherwise pointless review comment to a patch submission on a Linux kernel developer mailing list. I strongly suggest that you not do this anymore. Please do not bother developers who are actively working to produce patches and features with comments that, in the end, are a waste of time.

Patch submitter, please ignore Markus's suggestion; you do not need to follow it at all. The person/bot/AI that sent it is being ignored by almost all Linux kernel maintainers for having a persistent pattern of behavior of producing distracting and pointless commentary, and inability to adapt to feedback. Please feel free to also ignore emails from them.

thanks,

greg k-h's patch email bot

Hi Dmitry,
what are your thoughts on Abhishek's comment? I think we should attempt to register the alternate mode when CONFIG_TYPEC_DP_ALTMODE is not enabled. It would give us a more accurate representation of the partner in user space. I understand your point about ignoring a potential EOPNOTSUPP response from the non-stub function. What if we leave ucsi.c alone, and replace the stub function's null return with a call to typec_port_register_altmode(). That would register DP altmode as an unsupported mode when CONFIG_TYPEC_DP_ALTMODE is not enabled, and fix the null pointer dereference. But, it won't change behavior when CONFIG_TYPEC_DP_ALTMODE is enabled.

Hi Markus,
thanks for your feedback. I'll update the commit message to say "null pointer dereference" when I upload a v3 series.

Thanks,
Jameson

Yes, this sounds like a perfect idea!

With best wishes
Dmitry

Great! I'll post a v3 series applying this shortly.

Thanks,
Jameson

This is not the correct way to fix this. The normal thing to do would be to add NULL checks.

https://staticthinking.wordpress.com/2022/08/01/mixing-error-pointers-and-null/'

regards,
dan carpenter

Hi Dan,
thank you for the reference. In this case I think returning NULL from ucsi_register_displayport stub and using a NULL check to prevent a NULL pointer dereference won't give us the desired behavior. When CONFIG_TYPEC_DP_ALTMODE is not enabled, the function would return NULL and the UCSI driver will never end up registering DisplayPort alternate mode. I'll update the commit message to note that this patch adds a fallback registration for DisplayPort alternate mode in addition to simply fixing the NULL pointer dereference caused by returning it in the ucsi_register_displayport stub. Separately we could add a NULL check, but I don't think it's necessary. Neither the non-stub ucsi_register_displayport or typec_port_register_altmode look like they will return NULL.

Thanks,
Jameson

It looks like in v3 you changed this to:

- return NULL;
+ return typec_port_register_altmode(con->port, desc);

Which is fine. Returning a special error pointer which means success is the part that I objected to.

regards,
dan carpenter

From: Abhishek Pandit-Subedi <[email protected]>

When adding altmode ops, update the sysfs group so that visibility is also recalculated.

---
Changes in V2:
- None.

 drivers/usb/typec/altmodes/displayport.c |  2 +-
 drivers/usb/typec/class.c                | 18 +++++++++++++++++-
 drivers/usb/typec/ucsi/displayport.c     |  2 +-
 include/linux/usb/typec.h                |  3 +++
 4 files changed, 22 insertions(+), 3 deletions(-)

index 596cd4806018b..92cc1b1361208 100644
@@ -746,7 +746,7 @@ int dp_altmode_probe(struct typec_altmode *alt)
 	dp->alt = alt;
 
 	alt->desc = "DisplayPort";
-	alt->ops = &dp_altmode_ops;
+	typec_altmode_set_ops(alt, &dp_altmode_ops);
 
 	if (plug) {
 		plug->desc = "Displayport";

index 9610e647a8d48..9262fcd4144f8 100644
@@ -467,6 +467,22 @@ static const struct attribute_group *typec_altmode_groups[] = {
 	NULL
 };
 
+/**
+ * typec_altmode_set_ops - Set ops for altmode
+ * @adev: Handle to the alternate mode
+ * @ops: Ops for the alternate mode
+ *
+ * After setting ops, attribute visiblity needs to be refreshed if the alternate
+ * mode can be activated.
+ */
+void typec_altmode_set_ops(struct typec_altmode *adev,
+			   const struct typec_altmode_ops *ops)
+{
+	adev->ops = ops;
+	sysfs_update_group(&adev->dev.kobj, &typec_altmode_group);
+}
+EXPORT_SYMBOL_GPL(typec_altmode_set_ops);
+
 static int altmode_id_get(struct device *dev)
 {
 	struct ida *ids;

@@ -2317,7 +2333,7 @@ void typec_port_register_altmodes(struct typec_port *port,
 			continue;
 		}
 
-		alt->ops = ops;
+		typec_altmode_set_ops(alt, ops);
 		typec_altmode_set_drvdata(alt, drvdata);
 		altmodes[index] = alt;
 		index++;

index d9d3c91125ca8..eb7b8d6e47d00 100644
@@ -337,7 +337,7 @@ struct typec_altmode *ucsi_register_displayport(struct ucsi_connector *con,
 	dp->con = con;
 	dp->alt = alt;
 
-	alt->ops = &ucsi_displayport_ops;
+	typec_altmode_set_ops(alt, &ucsi_displayport_ops);
 	typec_altmode_set_drvdata(alt, dp);
 
 	return alt;

index b35b427561ab5..549275f8ac1b3 100644
@@ -167,6 +167,9 @@ struct typec_port *typec_altmode2port(struct typec_altmode *alt);
 
 void typec_altmode_update_active(struct typec_altmode *alt, bool active);
 
+void typec_altmode_set_ops(struct typec_altmode *alt,
+			   const struct typec_altmode_ops *ops);
+
 enum typec_plug_index {
 	TYPEC_PLUG_SOP_P,
 	TYPEC_PLUG_SOP_PP,

2.44.0.769.g3c40516874-goog

Delay the ucsi_check_altmodes task to be inline with surrounding partner tasks. This allows partner, cable and identity discovery to complete before alternate mode registration. With that order, alternate mode discovery can be used to indicate the ucsi driver has completed discovery.

---
Changes in V2:
- None.

 drivers/usb/typec/ucsi/ucsi.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index f3b413f94fd28..f167891e3f79d 100644
@@ -966,7 +966,7 @@ static void ucsi_pwr_opmode_change(struct ucsi_connector *con)
 		con->rdo = con->status.request_data_obj;
 		typec_set_pwr_opmode(con->port, TYPEC_PWR_MODE_PD);
 		ucsi_partner_task(con, ucsi_get_src_pdos, 30, 0);
-		ucsi_partner_task(con, ucsi_check_altmodes, 30, 0);
+		ucsi_partner_task(con, ucsi_check_altmodes, 30, HZ);
 		ucsi_partner_task(con, ucsi_register_partner_pdos, 1, HZ);
 		break;
 	case UCSI_CONSTAT_PWR_OPMODE_TYPEC1_5:

@@ -1250,7 +1250,7 @@ static void ucsi_handle_connector_change(struct work_struct *work)
 	}
 
 	if (con->status.change & UCSI_CONSTAT_CAM_CHANGE)
-		ucsi_partner_task(con, ucsi_check_altmodes, 1, 0);
+		ucsi_partner_task(con, ucsi_check_altmodes, 1, HZ);
 
 out_unlock:
 	mutex_unlock(&con->lock);

2.44.0.769.g3c40516874-goog

Providing the number of known alternate modes allows user space to determine when device registration has completed. Always register a number of known alternate modes for the partner and cable plug, even when the number of supported alternate modes is 0.

---
Changes in V2:
- None.

 drivers/usb/typec/ucsi/ucsi.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

index f167891e3f79d..994b8a6b6be96 100644
@@ -815,10 +815,11 @@ static int ucsi_check_altmodes(struct ucsi_connector *con)
 	/* Ignoring the errors in this case. */
 	if (con->partner_altmode[0]) {
 		num_partner_am = ucsi_get_num_altmode(con->partner_altmode);
-		if (num_partner_am > 0)
-			typec_partner_set_num_altmodes(con->partner, num_partner_am);
+		typec_partner_set_num_altmodes(con->partner, num_partner_am);
 		ucsi_altmode_update_active(con);
 		return 0;
+	} else {
+		typec_partner_set_num_altmodes(con->partner, 0);
 	}
 
 	return ret;

@@ -1141,7 +1142,7 @@ static int ucsi_check_connection(struct ucsi_connector *con)
 static int ucsi_check_cable(struct ucsi_connector *con)
 {
 	u64 command;
-	int ret;
+	int ret, num_plug_am;
 
 	if (con->cable)
 		return 0;

@@ -1175,6 +1176,13 @@ static int ucsi_check_cable(struct ucsi_connector *con)
 			return ret;
 	}
 
+	if (con->plug_altmode[0]) {
+		num_plug_am = ucsi_get_num_altmode(con->plug_altmode);
+		typec_plug_set_num_altmodes(con->plug, num_plug_am);
+	} else {
+		typec_plug_set_num_altmodes(con->plug, 0);
+	}
+
 	return 0;
 }
 

2.44.0.769.g3c40516874-goog