[PATCH v6 0/4] driver core: add probe error check helper

[PATCH v6 0/4] driver core: add probe error check helper

[Andrzej Hajda]

Hi All,

Thanks for multiple comments.

Changes since v5:
- removed patch adding macro, dev_err_probe(dev, PTR_ERR(ptr), ...) should be used instead,
- added dev_dbg logging in case of -EPROBE_DEFER,
- renamed functions and vars according to comments,
- extended docs,
- cosmetics.

Original message (with small adjustments):

Recently I took some time to re-check error handling in drivers probe code,
and I have noticed that number of incorrect resource acquisition error handling
increased and there are no other propositions which can cure the situation.

So I have decided to resend my old proposition of probe_err helper which should
simplify resource acquisition error handling, it also extend it with adding defer
probe reason to devices_deferred debugfs property, which should improve debugging
experience for developers/testers.

I have also added two patches showing usage and benefits of the helper.

My dirty/ad-hoc cocci scripts shows that this helper can be used in at least 2700 places
saving about 3500 lines of code.

Regards
Andrzej


Andrzej Hajda (4):
  driver core: add device probe log helper
  driver core: add deferring probe reason to devices_deferred property
  drm/bridge/sii8620: fix resource acquisition error handling
  drm/bridge: lvds-codec: simplify error handling

 drivers/base/base.h                  |  3 ++
 drivers/base/core.c                  | 46 ++++++++++++++++++++++++++++
 drivers/base/dd.c                    | 23 +++++++++++++-
 drivers/gpu/drm/bridge/lvds-codec.c  | 10 ++----
 drivers/gpu/drm/bridge/sil-sii8620.c | 21 ++++++-------
 include/linux/device.h               |  3 ++
 6 files changed, 86 insertions(+), 20 deletions(-)

-- 
2.17.1


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[PATCH v6 1/4] driver core: add device probe log helper

[Andrzej Hajda]

During probe every time driver gets resource it should usually check for
error printk some message if it is not -EPROBE_DEFER and return the error.
This pattern is simple but requires adding few lines after any resource
acquisition code, as a result it is often omitted or implemented only
partially.
dev_err_probe helps to replace such code sequences with simple call,
so code:
	if (err != -EPROBE_DEFER)
		dev_err(dev, ...);
	return err;
becomes:
	return probe_err(dev, err, ...);

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
---
 drivers/base/core.c    | 42 ++++++++++++++++++++++++++++++++++++++++++
 include/linux/device.h |  3 +++
 2 files changed, 45 insertions(+)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 67d39a90b45c..3a827c82933f 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -3953,6 +3953,48 @@ define_dev_printk_level(_dev_info, KERN_INFO);
 
 #endif
 
+/**
+ * dev_err_probe - probe error check and log helper
+ * @dev: the pointer to the struct device
+ * @err: error value to test
+ * @fmt: printf-style format string
+ * @...: arguments as specified in the format string
+ *
+ * This helper implements common pattern present in probe functions for error
+ * checking: print debug or error message depending if the error value is
+ * -EPROBE_DEFER and propagate error upwards.
+ * It replaces code sequence:
+ * 	if (err != -EPROBE_DEFER)
+ * 		dev_err(dev, ...);
+ * 	else
+ * 		dev_dbg(dev, ...);
+ * 	return err;
+ * with
+ * 	return dev_err_probe(dev, err, ...);
+ *
+ * Returns @err.
+ *
+ */
+int dev_err_probe(const struct device *dev, int err, const char *fmt, ...)
+{
+	struct va_format vaf;
+	va_list args;
+
+	va_start(args, fmt);
+	vaf.fmt = fmt;
+	vaf.va = &args;
+
+	if (err != -EPROBE_DEFER)
+		dev_err(dev, "error %d: %pV", err, &vaf);
+	else
+		dev_dbg(dev, "error %d: %pV", err, &vaf);
+
+	va_end(args);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(dev_err_probe);
+
 static inline bool fwnode_is_primary(struct fwnode_handle *fwnode)
 {
 	return fwnode && !IS_ERR(fwnode->secondary);
diff --git a/include/linux/device.h b/include/linux/device.h
index 15460a5ac024..6b2272ae9af8 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -964,6 +964,9 @@ void device_link_remove(void *consumer, struct device *supplier);
 void device_links_supplier_sync_state_pause(void);
 void device_links_supplier_sync_state_resume(void);
 
+extern __printf(3, 4)
+int dev_err_probe(const struct device *dev, int err, const char *fmt, ...);
+
 /* Create alias, so I can be autoloaded. */
 #define MODULE_ALIAS_CHARDEV(major,minor) \
 	MODULE_ALIAS("char-major-" __stringify(major) "-" __stringify(minor))
-- 
2.17.1


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Re: [PATCH v6 1/4] driver core: add device probe log helper

[Rafael J. Wysocki]

On Fri, Jun 26, 2020 at 12:01 PM Andrzej Hajda <a.hajda@samsung.com> wrote:
>
> During probe every time driver gets resource it should usually check for
> error printk some message if it is not -EPROBE_DEFER and return the error.
> This pattern is simple but requires adding few lines after any resource
> acquisition code, as a result it is often omitted or implemented only
> partially.
> dev_err_probe helps to replace such code sequences with simple call,
> so code:
>         if (err != -EPROBE_DEFER)
>                 dev_err(dev, ...);
>         return err;
> becomes:
>         return probe_err(dev, err, ...);
>
> Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>

Reviewed-by: Rafael J. Wysocki <rafael@kernel.org>

> ---
>  drivers/base/core.c    | 42 ++++++++++++++++++++++++++++++++++++++++++
>  include/linux/device.h |  3 +++
>  2 files changed, 45 insertions(+)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 67d39a90b45c..3a827c82933f 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -3953,6 +3953,48 @@ define_dev_printk_level(_dev_info, KERN_INFO);
>
>  #endif
>
> +/**
> + * dev_err_probe - probe error check and log helper
> + * @dev: the pointer to the struct device
> + * @err: error value to test
> + * @fmt: printf-style format string
> + * @...: arguments as specified in the format string
> + *
> + * This helper implements common pattern present in probe functions for error
> + * checking: print debug or error message depending if the error value is
> + * -EPROBE_DEFER and propagate error upwards.
> + * It replaces code sequence:
> + *     if (err != -EPROBE_DEFER)
> + *             dev_err(dev, ...);
> + *     else
> + *             dev_dbg(dev, ...);
> + *     return err;
> + * with
> + *     return dev_err_probe(dev, err, ...);
> + *
> + * Returns @err.
> + *
> + */
> +int dev_err_probe(const struct device *dev, int err, const char *fmt, ...)
> +{
> +       struct va_format vaf;
> +       va_list args;
> +
> +       va_start(args, fmt);
> +       vaf.fmt = fmt;
> +       vaf.va = &args;
> +
> +       if (err != -EPROBE_DEFER)
> +               dev_err(dev, "error %d: %pV", err, &vaf);
> +       else
> +               dev_dbg(dev, "error %d: %pV", err, &vaf);
> +
> +       va_end(args);
> +
> +       return err;
> +}
> +EXPORT_SYMBOL_GPL(dev_err_probe);
> +
>  static inline bool fwnode_is_primary(struct fwnode_handle *fwnode)
>  {
>         return fwnode && !IS_ERR(fwnode->secondary);
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 15460a5ac024..6b2272ae9af8 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -964,6 +964,9 @@ void device_link_remove(void *consumer, struct device *supplier);
>  void device_links_supplier_sync_state_pause(void);
>  void device_links_supplier_sync_state_resume(void);
>
> +extern __printf(3, 4)
> +int dev_err_probe(const struct device *dev, int err, const char *fmt, ...);
> +
>  /* Create alias, so I can be autoloaded. */
>  #define MODULE_ALIAS_CHARDEV(major,minor) \
>         MODULE_ALIAS("char-major-" __stringify(major) "-" __stringify(minor))
> --
> 2.17.1
>

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Re: [PATCH v6 1/4] driver core: add device probe log helper

[Sam Ravnborg]

Hi Andrzej

On Fri, Jun 26, 2020 at 12:01:00PM +0200, Andrzej Hajda wrote:
> During probe every time driver gets resource it should usually check for
> error printk some message if it is not -EPROBE_DEFER and return the error.
> This pattern is simple but requires adding few lines after any resource
> acquisition code, as a result it is often omitted or implemented only
> partially.
> dev_err_probe helps to replace such code sequences with simple call,
> so code:
> 	if (err != -EPROBE_DEFER)
> 		dev_err(dev, ...);
> 	return err;
> becomes:
> 	return probe_err(dev, err, ...);
s/probe_err/dev_err_probe/

	Sam
> 
> Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
> ---
>  drivers/base/core.c    | 42 ++++++++++++++++++++++++++++++++++++++++++
>  include/linux/device.h |  3 +++
>  2 files changed, 45 insertions(+)
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 67d39a90b45c..3a827c82933f 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -3953,6 +3953,48 @@ define_dev_printk_level(_dev_info, KERN_INFO);
>  
>  #endif
>  
> +/**
> + * dev_err_probe - probe error check and log helper
> + * @dev: the pointer to the struct device
> + * @err: error value to test
> + * @fmt: printf-style format string
> + * @...: arguments as specified in the format string
> + *
> + * This helper implements common pattern present in probe functions for error
> + * checking: print debug or error message depending if the error value is
> + * -EPROBE_DEFER and propagate error upwards.
> + * It replaces code sequence:
> + * 	if (err != -EPROBE_DEFER)
> + * 		dev_err(dev, ...);
> + * 	else
> + * 		dev_dbg(dev, ...);
> + * 	return err;
> + * with
> + * 	return dev_err_probe(dev, err, ...);
> + *
> + * Returns @err.
> + *
> + */
> +int dev_err_probe(const struct device *dev, int err, const char *fmt, ...)
> +{
> +	struct va_format vaf;
> +	va_list args;
> +
> +	va_start(args, fmt);
> +	vaf.fmt = fmt;
> +	vaf.va = &args;
> +
> +	if (err != -EPROBE_DEFER)
> +		dev_err(dev, "error %d: %pV", err, &vaf);
> +	else
> +		dev_dbg(dev, "error %d: %pV", err, &vaf);
> +
> +	va_end(args);
> +
> +	return err;
> +}
> +EXPORT_SYMBOL_GPL(dev_err_probe);
> +
>  static inline bool fwnode_is_primary(struct fwnode_handle *fwnode)
>  {
>  	return fwnode && !IS_ERR(fwnode->secondary);
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 15460a5ac024..6b2272ae9af8 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -964,6 +964,9 @@ void device_link_remove(void *consumer, struct device *supplier);
>  void device_links_supplier_sync_state_pause(void);
>  void device_links_supplier_sync_state_resume(void);
>  
> +extern __printf(3, 4)
> +int dev_err_probe(const struct device *dev, int err, const char *fmt, ...);
> +
>  /* Create alias, so I can be autoloaded. */
>  #define MODULE_ALIAS_CHARDEV(major,minor) \
>  	MODULE_ALIAS("char-major-" __stringify(major) "-" __stringify(minor))
> -- 
> 2.17.1
> 
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

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Re: [PATCH v6 1/4] driver core: add device probe log helper

[Grygorii Strashko]

On 26/06/2020 13:01, Andrzej Hajda wrote:
> During probe every time driver gets resource it should usually check for
> error printk some message if it is not -EPROBE_DEFER and return the error.
> This pattern is simple but requires adding few lines after any resource
> acquisition code, as a result it is often omitted or implemented only
> partially.
> dev_err_probe helps to replace such code sequences with simple call,
> so code:
> 	if (err != -EPROBE_DEFER)
> 		dev_err(dev, ...);
> 	return err;
> becomes:
> 	return probe_err(dev, err, ...);
> 
> Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
> ---
>   drivers/base/core.c    | 42 ++++++++++++++++++++++++++++++++++++++++++
>   include/linux/device.h |  3 +++
>   2 files changed, 45 insertions(+)
> 

Basic version of the helper looks very good to me, thank you.
Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>

> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 67d39a90b45c..3a827c82933f 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -3953,6 +3953,48 @@ define_dev_printk_level(_dev_info, KERN_INFO);
>   
>   #endif
>   
> +/**
> + * dev_err_probe - probe error check and log helper
> + * @dev: the pointer to the struct device
> + * @err: error value to test
> + * @fmt: printf-style format string
> + * @...: arguments as specified in the format string
> + *
> + * This helper implements common pattern present in probe functions for error
> + * checking: print debug or error message depending if the error value is
> + * -EPROBE_DEFER and propagate error upwards.
> + * It replaces code sequence:
> + * 	if (err != -EPROBE_DEFER)
> + * 		dev_err(dev, ...);
> + * 	else
> + * 		dev_dbg(dev, ...);
> + * 	return err;
> + * with
> + * 	return dev_err_probe(dev, err, ...);
> + *
> + * Returns @err.
> + *
> + */
> +int dev_err_probe(const struct device *dev, int err, const char *fmt, ...)
> +{
> +	struct va_format vaf;
> +	va_list args;
> +
> +	va_start(args, fmt);
> +	vaf.fmt = fmt;
> +	vaf.va = &args;
> +
> +	if (err != -EPROBE_DEFER)
> +		dev_err(dev, "error %d: %pV", err, &vaf);
> +	else
> +		dev_dbg(dev, "error %d: %pV", err, &vaf);
> +
> +	va_end(args);
> +
> +	return err;
> +}
> +EXPORT_SYMBOL_GPL(dev_err_probe);
> +
>   static inline bool fwnode_is_primary(struct fwnode_handle *fwnode)
>   {
>   	return fwnode && !IS_ERR(fwnode->secondary);
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 15460a5ac024..6b2272ae9af8 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -964,6 +964,9 @@ void device_link_remove(void *consumer, struct device *supplier);
>   void device_links_supplier_sync_state_pause(void);
>   void device_links_supplier_sync_state_resume(void);
>   
> +extern __printf(3, 4)
> +int dev_err_probe(const struct device *dev, int err, const char *fmt, ...);
> +
>   /* Create alias, so I can be autoloaded. */
>   #define MODULE_ALIAS_CHARDEV(major,minor) \
>   	MODULE_ALIAS("char-major-" __stringify(major) "-" __stringify(minor))
> 

-- 
Best regards,
grygorii

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[PATCH v6 2/4] driver core: add deferring probe reason to devices_deferred property

[Andrzej Hajda]

/sys/kernel/debug/devices_deferred property contains list of deferred devices.
This list does not contain reason why the driver deferred probe, the patch
improves it.
The natural place to set the reason is probe_err function introduced recently,
ie. if probe_err will be called with -EPROBE_DEFER instead of printk the message
will be attached to deferred device and printed when user read devices_deferred
property.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
---
 drivers/base/base.h |  3 +++
 drivers/base/core.c |  8 ++++++--
 drivers/base/dd.c   | 23 ++++++++++++++++++++++-
 3 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/drivers/base/base.h b/drivers/base/base.h
index 95c22c0f9036..6954fccab3d7 100644
--- a/drivers/base/base.h
+++ b/drivers/base/base.h
@@ -93,6 +93,7 @@ struct device_private {
 	struct klist_node knode_class;
 	struct list_head deferred_probe;
 	struct device_driver *async_driver;
+	char *deferred_probe_reason;
 	struct device *device;
 	u8 dead:1;
 };
@@ -134,6 +135,8 @@ extern void device_release_driver_internal(struct device *dev,
 extern void driver_detach(struct device_driver *drv);
 extern int driver_probe_device(struct device_driver *drv, struct device *dev);
 extern void driver_deferred_probe_del(struct device *dev);
+extern void device_set_deferred_probe_reson(const struct device *dev,
+					    struct va_format *vaf);
 static inline int driver_match_device(struct device_driver *drv,
 				      struct device *dev)
 {
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 3a827c82933f..fee047f03681 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -3963,6 +3963,8 @@ define_dev_printk_level(_dev_info, KERN_INFO);
  * This helper implements common pattern present in probe functions for error
  * checking: print debug or error message depending if the error value is
  * -EPROBE_DEFER and propagate error upwards.
+ * In case of -EPROBE_DEFER it sets also defer probe reason, which can be
+ * checked later by reading devices_deferred debugfs attribute.
  * It replaces code sequence:
  * 	if (err != -EPROBE_DEFER)
  * 		dev_err(dev, ...);
@@ -3984,10 +3986,12 @@ int dev_err_probe(const struct device *dev, int err, const char *fmt, ...)
 	vaf.fmt = fmt;
 	vaf.va = &args;
 
-	if (err != -EPROBE_DEFER)
+	if (err != -EPROBE_DEFER) {
 		dev_err(dev, "error %d: %pV", err, &vaf);
-	else
+	} else {
+		device_set_deferred_probe_reson(dev, &vaf);
 		dev_dbg(dev, "error %d: %pV", err, &vaf);
+	}
 
 	va_end(args);
 
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 9a1d940342ac..dd5683b61f74 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -27,6 +27,7 @@
 #include <linux/async.h>
 #include <linux/pm_runtime.h>
 #include <linux/pinctrl/devinfo.h>
+#include <linux/slab.h>
 
 #include "base.h"
 #include "power/power.h"
@@ -136,6 +137,8 @@ void driver_deferred_probe_del(struct device *dev)
 	if (!list_empty(&dev->p->deferred_probe)) {
 		dev_dbg(dev, "Removed from deferred list\n");
 		list_del_init(&dev->p->deferred_probe);
+		kfree(dev->p->deferred_probe_reason);
+		dev->p->deferred_probe_reason = NULL;
 	}
 	mutex_unlock(&deferred_probe_mutex);
 }
@@ -211,6 +214,23 @@ void device_unblock_probing(void)
 	driver_deferred_probe_trigger();
 }
 
+/**
+ * device_set_deferred_probe_reson() - Set defer probe reason message for device
+ * @dev: the pointer to the struct device
+ * @vaf: the pointer to va_format structure with message
+ */
+void device_set_deferred_probe_reson(const struct device *dev, struct va_format *vaf)
+{
+	const char *drv = dev_driver_string(dev);
+
+	mutex_lock(&deferred_probe_mutex);
+
+	kfree(dev->p->deferred_probe_reason);
+	dev->p->deferred_probe_reason = kasprintf(GFP_KERNEL, "%s: %pV", drv, vaf);
+
+	mutex_unlock(&deferred_probe_mutex);
+}
+
 /*
  * deferred_devs_show() - Show the devices in the deferred probe pending list.
  */
@@ -221,7 +241,8 @@ static int deferred_devs_show(struct seq_file *s, void *data)
 	mutex_lock(&deferred_probe_mutex);
 
 	list_for_each_entry(curr, &deferred_probe_pending_list, deferred_probe)
-		seq_printf(s, "%s\n", dev_name(curr->device));
+		seq_printf(s, "%s\t%s", dev_name(curr->device),
+			   curr->device->p->deferred_probe_reason ?: "\n");
 
 	mutex_unlock(&deferred_probe_mutex);
 
-- 
2.17.1


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Re: [PATCH v6 2/4] driver core: add deferring probe reason to devices_deferred property

[Rafael J. Wysocki]

On Fri, Jun 26, 2020 at 12:01 PM Andrzej Hajda <a.hajda@samsung.com> wrote:
>
> /sys/kernel/debug/devices_deferred property contains list of deferred devices.
> This list does not contain reason why the driver deferred probe, the patch
> improves it.
> The natural place to set the reason is probe_err function introduced recently,
> ie. if probe_err will be called with -EPROBE_DEFER instead of printk the message
> will be attached to deferred device and printed when user read devices_deferred
> property.
>
> Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
> Reviewed-by: Mark Brown <broonie@kernel.org>
> Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
> Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>

Reviewed-by: Rafael J. Wysocki <rafael@kernel.org>

> ---
>  drivers/base/base.h |  3 +++
>  drivers/base/core.c |  8 ++++++--
>  drivers/base/dd.c   | 23 ++++++++++++++++++++++-
>  3 files changed, 31 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/base/base.h b/drivers/base/base.h
> index 95c22c0f9036..6954fccab3d7 100644
> --- a/drivers/base/base.h
> +++ b/drivers/base/base.h
> @@ -93,6 +93,7 @@ struct device_private {
>         struct klist_node knode_class;
>         struct list_head deferred_probe;
>         struct device_driver *async_driver;
> +       char *deferred_probe_reason;
>         struct device *device;
>         u8 dead:1;
>  };
> @@ -134,6 +135,8 @@ extern void device_release_driver_internal(struct device *dev,
>  extern void driver_detach(struct device_driver *drv);
>  extern int driver_probe_device(struct device_driver *drv, struct device *dev);
>  extern void driver_deferred_probe_del(struct device *dev);
> +extern void device_set_deferred_probe_reson(const struct device *dev,
> +                                           struct va_format *vaf);
>  static inline int driver_match_device(struct device_driver *drv,
>                                       struct device *dev)
>  {
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 3a827c82933f..fee047f03681 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -3963,6 +3963,8 @@ define_dev_printk_level(_dev_info, KERN_INFO);
>   * This helper implements common pattern present in probe functions for error
>   * checking: print debug or error message depending if the error value is
>   * -EPROBE_DEFER and propagate error upwards.
> + * In case of -EPROBE_DEFER it sets also defer probe reason, which can be
> + * checked later by reading devices_deferred debugfs attribute.
>   * It replaces code sequence:
>   *     if (err != -EPROBE_DEFER)
>   *             dev_err(dev, ...);
> @@ -3984,10 +3986,12 @@ int dev_err_probe(const struct device *dev, int err, const char *fmt, ...)
>         vaf.fmt = fmt;
>         vaf.va = &args;
>
> -       if (err != -EPROBE_DEFER)
> +       if (err != -EPROBE_DEFER) {
>                 dev_err(dev, "error %d: %pV", err, &vaf);
> -       else
> +       } else {
> +               device_set_deferred_probe_reson(dev, &vaf);
>                 dev_dbg(dev, "error %d: %pV", err, &vaf);
> +       }
>
>         va_end(args);
>
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 9a1d940342ac..dd5683b61f74 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -27,6 +27,7 @@
>  #include <linux/async.h>
>  #include <linux/pm_runtime.h>
>  #include <linux/pinctrl/devinfo.h>
> +#include <linux/slab.h>
>
>  #include "base.h"
>  #include "power/power.h"
> @@ -136,6 +137,8 @@ void driver_deferred_probe_del(struct device *dev)
>         if (!list_empty(&dev->p->deferred_probe)) {
>                 dev_dbg(dev, "Removed from deferred list\n");
>                 list_del_init(&dev->p->deferred_probe);
> +               kfree(dev->p->deferred_probe_reason);
> +               dev->p->deferred_probe_reason = NULL;
>         }
>         mutex_unlock(&deferred_probe_mutex);
>  }
> @@ -211,6 +214,23 @@ void device_unblock_probing(void)
>         driver_deferred_probe_trigger();
>  }
>
> +/**
> + * device_set_deferred_probe_reson() - Set defer probe reason message for device
> + * @dev: the pointer to the struct device
> + * @vaf: the pointer to va_format structure with message
> + */
> +void device_set_deferred_probe_reson(const struct device *dev, struct va_format *vaf)
> +{
> +       const char *drv = dev_driver_string(dev);
> +
> +       mutex_lock(&deferred_probe_mutex);
> +
> +       kfree(dev->p->deferred_probe_reason);
> +       dev->p->deferred_probe_reason = kasprintf(GFP_KERNEL, "%s: %pV", drv, vaf);
> +
> +       mutex_unlock(&deferred_probe_mutex);
> +}
> +
>  /*
>   * deferred_devs_show() - Show the devices in the deferred probe pending list.
>   */
> @@ -221,7 +241,8 @@ static int deferred_devs_show(struct seq_file *s, void *data)
>         mutex_lock(&deferred_probe_mutex);
>
>         list_for_each_entry(curr, &deferred_probe_pending_list, deferred_probe)
> -               seq_printf(s, "%s\n", dev_name(curr->device));
> +               seq_printf(s, "%s\t%s", dev_name(curr->device),
> +                          curr->device->p->deferred_probe_reason ?: "\n");
>
>         mutex_unlock(&deferred_probe_mutex);
>
> --
> 2.17.1
>

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Re: [PATCH v6 2/4] driver core: add deferring probe reason to devices_deferred property

[Grygorii Strashko]

On 26/06/2020 13:01, Andrzej Hajda wrote:
> /sys/kernel/debug/devices_deferred property contains list of deferred devices.
> This list does not contain reason why the driver deferred probe, the patch
> improves it.
> The natural place to set the reason is probe_err function introduced recently,
> ie. if probe_err will be called with -EPROBE_DEFER instead of printk the message
> will be attached to deferred device and printed when user read devices_deferred
> property.
> 
> Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
> Reviewed-by: Mark Brown <broonie@kernel.org>
> Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
> Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
> ---
>   drivers/base/base.h |  3 +++
>   drivers/base/core.c |  8 ++++++--
>   drivers/base/dd.c   | 23 ++++++++++++++++++++++-
>   3 files changed, 31 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/base/base.h b/drivers/base/base.h
> index 95c22c0f9036..6954fccab3d7 100644
> --- a/drivers/base/base.h
> +++ b/drivers/base/base.h
> @@ -93,6 +93,7 @@ struct device_private {
>   	struct klist_node knode_class;
>   	struct list_head deferred_probe;
>   	struct device_driver *async_driver;
> +	char *deferred_probe_reason;
>   	struct device *device;
>   	u8 dead:1;
>   };
> @@ -134,6 +135,8 @@ extern void device_release_driver_internal(struct device *dev,
>   extern void driver_detach(struct device_driver *drv);
>   extern int driver_probe_device(struct device_driver *drv, struct device *dev);
>   extern void driver_deferred_probe_del(struct device *dev);
> +extern void device_set_deferred_probe_reson(const struct device *dev,
> +					    struct va_format *vaf);
>   static inline int driver_match_device(struct device_driver *drv,
>   				      struct device *dev)
>   {
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 3a827c82933f..fee047f03681 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -3963,6 +3963,8 @@ define_dev_printk_level(_dev_info, KERN_INFO);
>    * This helper implements common pattern present in probe functions for error
>    * checking: print debug or error message depending if the error value is
>    * -EPROBE_DEFER and propagate error upwards.
> + * In case of -EPROBE_DEFER it sets also defer probe reason, which can be
> + * checked later by reading devices_deferred debugfs attribute.
>    * It replaces code sequence:
>    * 	if (err != -EPROBE_DEFER)
>    * 		dev_err(dev, ...);
> @@ -3984,10 +3986,12 @@ int dev_err_probe(const struct device *dev, int err, const char *fmt, ...)
>   	vaf.fmt = fmt;
>   	vaf.va = &args;
>   
> -	if (err != -EPROBE_DEFER)
> +	if (err != -EPROBE_DEFER) {
>   		dev_err(dev, "error %d: %pV", err, &vaf);
> -	else
> +	} else {
> +		device_set_deferred_probe_reson(dev, &vaf);
>   		dev_dbg(dev, "error %d: %pV", err, &vaf);
> +	}
>   
>   	va_end(args);
>   
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index 9a1d940342ac..dd5683b61f74 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -27,6 +27,7 @@
>   #include <linux/async.h>
>   #include <linux/pm_runtime.h>
>   #include <linux/pinctrl/devinfo.h>
> +#include <linux/slab.h>
>   
>   #include "base.h"
>   #include "power/power.h"
> @@ -136,6 +137,8 @@ void driver_deferred_probe_del(struct device *dev)
>   	if (!list_empty(&dev->p->deferred_probe)) {
>   		dev_dbg(dev, "Removed from deferred list\n");
>   		list_del_init(&dev->p->deferred_probe);
> +		kfree(dev->p->deferred_probe_reason);
> +		dev->p->deferred_probe_reason = NULL;
>   	}
>   	mutex_unlock(&deferred_probe_mutex);
>   }
> @@ -211,6 +214,23 @@ void device_unblock_probing(void)
>   	driver_deferred_probe_trigger();
>   }
>   
> +/**
> + * device_set_deferred_probe_reson() - Set defer probe reason message for device
> + * @dev: the pointer to the struct device
> + * @vaf: the pointer to va_format structure with message
> + */
> +void device_set_deferred_probe_reson(const struct device *dev, struct va_format *vaf)
> +{
> +	const char *drv = dev_driver_string(dev);
> +
> +	mutex_lock(&deferred_probe_mutex);
> +
> +	kfree(dev->p->deferred_probe_reason);
> +	dev->p->deferred_probe_reason = kasprintf(GFP_KERNEL, "%s: %pV", drv, vaf);
> +
> +	mutex_unlock(&deferred_probe_mutex);
> +}
> +
>   /*
>    * deferred_devs_show() - Show the devices in the deferred probe pending list.
>    */
> @@ -221,7 +241,8 @@ static int deferred_devs_show(struct seq_file *s, void *data)
>   	mutex_lock(&deferred_probe_mutex);
>   
>   	list_for_each_entry(curr, &deferred_probe_pending_list, deferred_probe)
> -		seq_printf(s, "%s\n", dev_name(curr->device));
> +		seq_printf(s, "%s\t%s", dev_name(curr->device),
> +			   curr->device->p->deferred_probe_reason ?: "\n");
>   
>   	mutex_unlock(&deferred_probe_mutex);
>   
> 

Sry, may be i missing smth, but shouldn't it be optional
(CONFIG_DEBUG_FS is probably too generic).

-- 
Best regards,
grygorii

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Re: [PATCH v6 2/4] driver core: add deferring probe reason to devices_deferred property

[Andrzej Hajda]

Hi Grygorii,

(...)

>>   /*
>>    * deferred_devs_show() - Show the devices in the deferred probe 
>> pending list.
>>    */
>> @@ -221,7 +241,8 @@ static int deferred_devs_show(struct seq_file *s, 
>> void *data)
>>       mutex_lock(&deferred_probe_mutex);
>>         list_for_each_entry(curr, &deferred_probe_pending_list, 
>> deferred_probe)
>> -        seq_printf(s, "%s\n", dev_name(curr->device));
>> +        seq_printf(s, "%s\t%s", dev_name(curr->device),
>> +               curr->device->p->deferred_probe_reason ?: "\n");
>>         mutex_unlock(&deferred_probe_mutex);
>>
>
> Sry, may be i missing smth, but shouldn't it be optional
> (CONFIG_DEBUG_FS is probably too generic).
>

I am not sure what exactly are you referring to, but this patch does not 
add new property, it just extends functionality of existing one.


Regards

Andrzej



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Re: [PATCH v6 2/4] driver core: add deferring probe reason to devices_deferred property

[Grygorii Strashko]

Hi

On 29/06/2020 14:28, Andrzej Hajda wrote:
> Hi Grygorii,
> 
> (...)
> 
>>>    /*
>>>     * deferred_devs_show() - Show the devices in the deferred probe
>>> pending list.
>>>     */
>>> @@ -221,7 +241,8 @@ static int deferred_devs_show(struct seq_file *s,
>>> void *data)
>>>        mutex_lock(&deferred_probe_mutex);
>>>          list_for_each_entry(curr, &deferred_probe_pending_list,
>>> deferred_probe)
>>> -        seq_printf(s, "%s\n", dev_name(curr->device));
>>> +        seq_printf(s, "%s\t%s", dev_name(curr->device),
>>> +               curr->device->p->deferred_probe_reason ?: "\n");
>>>          mutex_unlock(&deferred_probe_mutex);
>>>
>>
>> Sry, may be i missing smth, but shouldn't it be optional
>> (CONFIG_DEBUG_FS is probably too generic).
>>
> 
> I am not sure what exactly are you referring to, but this patch does not
> add new property, it just extends functionality of existing one.

Sry, needed to be more specific.

You've added  device_set_deferred_probe_reson(dev, &vaf);
which expected to be used on every EPROBE_DEFER in dev_err_probe() in combination with

+       } else {
+               device_set_deferred_probe_reson(dev, &vaf);
                 dev_dbg(dev, "error %d: %pV", err, &vaf);

^^ dev_dbg() does not add any runtime overhead during boot unless enabled
+       }

But:

+void device_set_deferred_probe_reson(const struct device *dev, struct va_format *vaf)
+{
+       const char *drv = dev_driver_string(dev);
+
+       mutex_lock(&deferred_probe_mutex);
+
+       kfree(dev->p->deferred_probe_reason);
+       dev->p->deferred_probe_reason = kasprintf(GFP_KERNEL, "%s: %pV", drv, vaf);
+
+       mutex_unlock(&deferred_probe_mutex);
+}

^^ Adds locking, kfree() and kasprintf() for every deferred probe during boot and can't be disabled.

Right?


-- 
Best regards,
grygorii

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Re: [PATCH v6 2/4] driver core: add deferring probe reason to devices_deferred property

[Andrzej Hajda]

On 30.06.2020 10:59, Grygorii Strashko wrote:
> Hi
>
> On 29/06/2020 14:28, Andrzej Hajda wrote:
>> Hi Grygorii,
>>
>> (...)
>>
>>>>    /*
>>>>     * deferred_devs_show() - Show the devices in the deferred probe
>>>> pending list.
>>>>     */
>>>> @@ -221,7 +241,8 @@ static int deferred_devs_show(struct seq_file *s,
>>>> void *data)
>>>>        mutex_lock(&deferred_probe_mutex);
>>>>          list_for_each_entry(curr, &deferred_probe_pending_list,
>>>> deferred_probe)
>>>> -        seq_printf(s, "%s\n", dev_name(curr->device));
>>>> +        seq_printf(s, "%s\t%s", dev_name(curr->device),
>>>> + curr->device->p->deferred_probe_reason ?: "\n");
>>>>          mutex_unlock(&deferred_probe_mutex);
>>>>
>>>
>>> Sry, may be i missing smth, but shouldn't it be optional
>>> (CONFIG_DEBUG_FS is probably too generic).
>>>
>>
>> I am not sure what exactly are you referring to, but this patch does not
>> add new property, it just extends functionality of existing one.
>
> Sry, needed to be more specific.
>
> You've added  device_set_deferred_probe_reson(dev, &vaf);
> which expected to be used on every EPROBE_DEFER in dev_err_probe() in 
> combination with
>
> +       } else {
> +               device_set_deferred_probe_reson(dev, &vaf);
>                 dev_dbg(dev, "error %d: %pV", err, &vaf);
>
> ^^ dev_dbg() does not add any runtime overhead during boot unless enabled
> +       }
>
> But:
>
> +void device_set_deferred_probe_reson(const struct device *dev, struct 
> va_format *vaf)
> +{
> +       const char *drv = dev_driver_string(dev);
> +
> +       mutex_lock(&deferred_probe_mutex);
> +
> +       kfree(dev->p->deferred_probe_reason);
> +       dev->p->deferred_probe_reason = kasprintf(GFP_KERNEL, "%s: 
> %pV", drv, vaf);
> +
> +       mutex_unlock(&deferred_probe_mutex);
> +}
>
> ^^ Adds locking, kfree() and kasprintf() for every deferred probe 
> during boot and can't be disabled.
>
> Right?


Right, but usually the burden should be insignificant in comparison to 
probe time, so I do not think it is worth optimizing.


Regards

Andrzej


>
>

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Re: [PATCH v6 2/4] driver core: add deferring probe reason to devices_deferred property

[Dmitry Torokhov]

On Tue, Jun 30, 2020 at 8:42 AM Andrzej Hajda <a.hajda@samsung.com> wrote:
>
>
> On 30.06.2020 10:59, Grygorii Strashko wrote:
> > Hi
> >
> > On 29/06/2020 14:28, Andrzej Hajda wrote:
> >> Hi Grygorii,
> >>
> >> (...)
> >>
> >>>>    /*
> >>>>     * deferred_devs_show() - Show the devices in the deferred probe
> >>>> pending list.
> >>>>     */
> >>>> @@ -221,7 +241,8 @@ static int deferred_devs_show(struct seq_file *s,
> >>>> void *data)
> >>>>        mutex_lock(&deferred_probe_mutex);
> >>>>          list_for_each_entry(curr, &deferred_probe_pending_list,
> >>>> deferred_probe)
> >>>> -        seq_printf(s, "%s\n", dev_name(curr->device));
> >>>> +        seq_printf(s, "%s\t%s", dev_name(curr->device),
> >>>> + curr->device->p->deferred_probe_reason ?: "\n");
> >>>>          mutex_unlock(&deferred_probe_mutex);
> >>>>
> >>>
> >>> Sry, may be i missing smth, but shouldn't it be optional
> >>> (CONFIG_DEBUG_FS is probably too generic).
> >>>
> >>
> >> I am not sure what exactly are you referring to, but this patch does not
> >> add new property, it just extends functionality of existing one.
> >
> > Sry, needed to be more specific.
> >
> > You've added  device_set_deferred_probe_reson(dev, &vaf);
> > which expected to be used on every EPROBE_DEFER in dev_err_probe() in
> > combination with
> >
> > +       } else {
> > +               device_set_deferred_probe_reson(dev, &vaf);
> >                 dev_dbg(dev, "error %d: %pV", err, &vaf);
> >
> > ^^ dev_dbg() does not add any runtime overhead during boot unless enabled
> > +       }
> >
> > But:
> >
> > +void device_set_deferred_probe_reson(const struct device *dev, struct
> > va_format *vaf)
> > +{
> > +       const char *drv = dev_driver_string(dev);
> > +
> > +       mutex_lock(&deferred_probe_mutex);
> > +
> > +       kfree(dev->p->deferred_probe_reason);
> > +       dev->p->deferred_probe_reason = kasprintf(GFP_KERNEL, "%s:
> > %pV", drv, vaf);
> > +
> > +       mutex_unlock(&deferred_probe_mutex);
> > +}
> >
> > ^^ Adds locking, kfree() and kasprintf() for every deferred probe
> > during boot and can't be disabled.
> >
> > Right?
>
>
> Right, but usually the burden should be insignificant in comparison to
> probe time, so I do not think it is worth optimizing.

I do not think this is going to take. You are suggesting that we
modify pretty much every driver to supply this deferral reason, and I
doubt it will happen. Can we put this burden on providers that raise
the deferral? I.e. majority of code are using devm API now, so we most
likely know the device for which deferral is being raised. We can have
a list of deferral reasons and their devices and when in device code
once probe is done we could try reconciling it with the deferred
devicelist, and this would mean you only need to implement this in
gpiolib, regulator core, clocks core, etc.

Thanks.

-- 
Dmitry

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Re: [PATCH v6 2/4] driver core: add deferring probe reason to devices_deferred property

[Andrzej Hajda]

On 30.06.2020 20:00, Dmitry Torokhov wrote:
> On Tue, Jun 30, 2020 at 8:42 AM Andrzej Hajda <a.hajda@samsung.com> wrote:
>>
>> On 30.06.2020 10:59, Grygorii Strashko wrote:
>>> Hi
>>>
>>> On 29/06/2020 14:28, Andrzej Hajda wrote:
>>>> Hi Grygorii,
>>>>
>>>> (...)
>>>>
>>>>>>     /*
>>>>>>      * deferred_devs_show() - Show the devices in the deferred probe
>>>>>> pending list.
>>>>>>      */
>>>>>> @@ -221,7 +241,8 @@ static int deferred_devs_show(struct seq_file *s,
>>>>>> void *data)
>>>>>>         mutex_lock(&deferred_probe_mutex);
>>>>>>           list_for_each_entry(curr, &deferred_probe_pending_list,
>>>>>> deferred_probe)
>>>>>> -        seq_printf(s, "%s\n", dev_name(curr->device));
>>>>>> +        seq_printf(s, "%s\t%s", dev_name(curr->device),
>>>>>> + curr->device->p->deferred_probe_reason ?: "\n");
>>>>>>           mutex_unlock(&deferred_probe_mutex);
>>>>>>
>>>>> Sry, may be i missing smth, but shouldn't it be optional
>>>>> (CONFIG_DEBUG_FS is probably too generic).
>>>>>
>>>> I am not sure what exactly are you referring to, but this patch does not
>>>> add new property, it just extends functionality of existing one.
>>> Sry, needed to be more specific.
>>>
>>> You've added  device_set_deferred_probe_reson(dev, &vaf);
>>> which expected to be used on every EPROBE_DEFER in dev_err_probe() in
>>> combination with
>>>
>>> +       } else {
>>> +               device_set_deferred_probe_reson(dev, &vaf);
>>>                  dev_dbg(dev, "error %d: %pV", err, &vaf);
>>>
>>> ^^ dev_dbg() does not add any runtime overhead during boot unless enabled
>>> +       }
>>>
>>> But:
>>>
>>> +void device_set_deferred_probe_reson(const struct device *dev, struct
>>> va_format *vaf)
>>> +{
>>> +       const char *drv = dev_driver_string(dev);
>>> +
>>> +       mutex_lock(&deferred_probe_mutex);
>>> +
>>> +       kfree(dev->p->deferred_probe_reason);
>>> +       dev->p->deferred_probe_reason = kasprintf(GFP_KERNEL, "%s:
>>> %pV", drv, vaf);
>>> +
>>> +       mutex_unlock(&deferred_probe_mutex);
>>> +}
>>>
>>> ^^ Adds locking, kfree() and kasprintf() for every deferred probe
>>> during boot and can't be disabled.
>>>
>>> Right?
>>
>> Right, but usually the burden should be insignificant in comparison to
>> probe time, so I do not think it is worth optimizing.
> I do not think this is going to take. You are suggesting that we
> modify pretty much every driver to supply this deferral reason, and I
> doubt it will happen. Can we put this burden on providers that raise
> the deferral?


I wouldn't say they raise the deferral, they just inform resource is not 
yet available. Only device driver, and only in its probe function can 
"raise the deferral".


>   I.e. majority of code are using devm API now, so we most
> likely know the device for which deferral is being raised. We can have
> a list of deferral reasons and their devices and when in device code
> once probe is done we could try reconciling it with the deferred
> devicelist, and this would mean you only need to implement this in
> gpiolib, regulator core, clocks core, etc.


This patchset tries to solve simple issue - replace multiple lines of 
code present in multiple probe functions (additionally fixing lot of 
them) with single call and then enhance it little bit, nothing more.

What you are proposing is blurry at the moment for me, provider does not 
know if consumer want to defer,  or will continue working without 
missing resource, moreover some consumers can acquire resources after 
probe - again no probe deferral. Even if it will be done (it can be, for 
example by creating probe version of all resource get functions), it 
will require much more changes but finally it will look like:

res = devm_get_resource_from_probe(....)

if (IS_ERR(res))

     return PTR_ERR(res);

vs:

res = devm_get_resource(...)

if (IS_ERR(res))

     return dev_err_probe(dev, PTR_ERR(res), ...);


Regards

Andrzej


>
> Thanks.
>

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Re: [PATCH v6 2/4] driver core: add deferring probe reason to devices_deferred property

[Dmitry Torokhov]

On Thu, Jul 02, 2020 at 08:57:55AM +0200, Andrzej Hajda wrote:
> 
> On 30.06.2020 20:00, Dmitry Torokhov wrote:
> > On Tue, Jun 30, 2020 at 8:42 AM Andrzej Hajda <a.hajda@samsung.com> wrote:
> >>
> >> On 30.06.2020 10:59, Grygorii Strashko wrote:
> >>> Hi
> >>>
> >>> On 29/06/2020 14:28, Andrzej Hajda wrote:
> >>>> Hi Grygorii,
> >>>>
> >>>> (...)
> >>>>
> >>>>>>     /*
> >>>>>>      * deferred_devs_show() - Show the devices in the deferred probe
> >>>>>> pending list.
> >>>>>>      */
> >>>>>> @@ -221,7 +241,8 @@ static int deferred_devs_show(struct seq_file *s,
> >>>>>> void *data)
> >>>>>>         mutex_lock(&deferred_probe_mutex);
> >>>>>>           list_for_each_entry(curr, &deferred_probe_pending_list,
> >>>>>> deferred_probe)
> >>>>>> -        seq_printf(s, "%s\n", dev_name(curr->device));
> >>>>>> +        seq_printf(s, "%s\t%s", dev_name(curr->device),
> >>>>>> + curr->device->p->deferred_probe_reason ?: "\n");
> >>>>>>           mutex_unlock(&deferred_probe_mutex);
> >>>>>>
> >>>>> Sry, may be i missing smth, but shouldn't it be optional
> >>>>> (CONFIG_DEBUG_FS is probably too generic).
> >>>>>
> >>>> I am not sure what exactly are you referring to, but this patch does not
> >>>> add new property, it just extends functionality of existing one.
> >>> Sry, needed to be more specific.
> >>>
> >>> You've added  device_set_deferred_probe_reson(dev, &vaf);
> >>> which expected to be used on every EPROBE_DEFER in dev_err_probe() in
> >>> combination with
> >>>
> >>> +       } else {
> >>> +               device_set_deferred_probe_reson(dev, &vaf);
> >>>                  dev_dbg(dev, "error %d: %pV", err, &vaf);
> >>>
> >>> ^^ dev_dbg() does not add any runtime overhead during boot unless enabled
> >>> +       }
> >>>
> >>> But:
> >>>
> >>> +void device_set_deferred_probe_reson(const struct device *dev, struct
> >>> va_format *vaf)
> >>> +{
> >>> +       const char *drv = dev_driver_string(dev);
> >>> +
> >>> +       mutex_lock(&deferred_probe_mutex);
> >>> +
> >>> +       kfree(dev->p->deferred_probe_reason);
> >>> +       dev->p->deferred_probe_reason = kasprintf(GFP_KERNEL, "%s:
> >>> %pV", drv, vaf);
> >>> +
> >>> +       mutex_unlock(&deferred_probe_mutex);
> >>> +}
> >>>
> >>> ^^ Adds locking, kfree() and kasprintf() for every deferred probe
> >>> during boot and can't be disabled.
> >>>
> >>> Right?
> >>
> >> Right, but usually the burden should be insignificant in comparison to
> >> probe time, so I do not think it is worth optimizing.
> > I do not think this is going to take. You are suggesting that we
> > modify pretty much every driver to supply this deferral reason, and I
> > doubt it will happen. Can we put this burden on providers that raise
> > the deferral?
> 
> 
> I wouldn't say they raise the deferral, they just inform resource is not 
> yet available. Only device driver, and only in its probe function can 
> "raise the deferral".

Well, this is a matter of perspective. If devm_gpiod_get() returns
-EBUSY and this is returned to driver core, is it GPIO line signals that
line is busy, or is it the driver applies its knowledge. I say that in
majority of cases driver does not really get a say in this and simply
has to pass whatever error condition that is signalled by providers up
the stack.

I would consider whenever a driver does not propagate -EPROBE_DEFER to
the driver code a bug that needs fixing, because it should not degrade
functionality and/or performance just because we have not figured out
how to order probing properly and have to rely on deferrals.

> 
> 
> >   I.e. majority of code are using devm API now, so we most
> > likely know the device for which deferral is being raised. We can have
> > a list of deferral reasons and their devices and when in device code
> > once probe is done we could try reconciling it with the deferred
> > devicelist, and this would mean you only need to implement this in
> > gpiolib, regulator core, clocks core, etc.
> 
> 
> This patchset tries to solve simple issue - replace multiple lines of 
> code present in multiple probe functions (additionally fixing lot of 
> them) with single call and then enhance it little bit, nothing more.
> 
> What you are proposing is blurry at the moment for me, provider does not 
> know if consumer want to defer,

This is my point - the consumer does not get to decide. If deferral is
raised, it must be honored.

> or will continue working without missing resource,

Deferral does not mean resource does not exist and the driver has to get
by if it can. It means the resource is not ready, and even if the system
can work without it, it will not be working optimally.

> moreover some consumers can acquire resources after probe - again no
> probe deferral.

In this case we should not signal deferral either.

> Even if it will be done (it can be, for 
> example by creating probe version of all resource get functions), it 
> will require much more changes but finally it will look like:
> 
> res = devm_get_resource_from_probe(....)
> 
> if (IS_ERR(res))
> 
>      return PTR_ERR(res);
> 
> vs:
> 
> res = devm_get_resource(...)
> 
> if (IS_ERR(res))
> 
>      return dev_err_probe(dev, PTR_ERR(res), ...);

And we will need to adjust how many hundreds of drivers?

Consider that most drivers use devm_clk_get(), devm_gpiod_get() and
devm_regulator_get() and their friends. All these APIs already have
device for which resource is being allocated, and moreover their use
outside of probe() path is highly suspicious (because devm outside of
probe() typically result in unwinding in really surprising order). So if
you could stash device and deferral reason in a list and then scan this
list in driver core when handling the raised deferral you would not need
to change anything in individual drivers.

Hope this clears what I had in mind.

Thanks.

-- 
Dmitry

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Re: [PATCH v6 2/4] driver core: add deferring probe reason to devices_deferred property

[Andrzej Hajda]

On 07.07.2020 06:14, Dmitry Torokhov wrote:
> On Thu, Jul 02, 2020 at 08:57:55AM +0200, Andrzej Hajda wrote:
>> On 30.06.2020 20:00, Dmitry Torokhov wrote:
>>> On Tue, Jun 30, 2020 at 8:42 AM Andrzej Hajda <a.hajda@samsung.com> wrote:
>>>> On 30.06.2020 10:59, Grygorii Strashko wrote:
>>>>> Hi
>>>>>
>>>>> On 29/06/2020 14:28, Andrzej Hajda wrote:
>>>>>> Hi Grygorii,
>>>>>>
>>>>>> (...)
>>>>>>
>>>>>>>>      /*
>>>>>>>>       * deferred_devs_show() - Show the devices in the deferred probe
>>>>>>>> pending list.
>>>>>>>>       */
>>>>>>>> @@ -221,7 +241,8 @@ static int deferred_devs_show(struct seq_file *s,
>>>>>>>> void *data)
>>>>>>>>          mutex_lock(&deferred_probe_mutex);
>>>>>>>>            list_for_each_entry(curr, &deferred_probe_pending_list,
>>>>>>>> deferred_probe)
>>>>>>>> -        seq_printf(s, "%s\n", dev_name(curr->device));
>>>>>>>> +        seq_printf(s, "%s\t%s", dev_name(curr->device),
>>>>>>>> + curr->device->p->deferred_probe_reason ?: "\n");
>>>>>>>>            mutex_unlock(&deferred_probe_mutex);
>>>>>>>>
>>>>>>> Sry, may be i missing smth, but shouldn't it be optional
>>>>>>> (CONFIG_DEBUG_FS is probably too generic).
>>>>>>>
>>>>>> I am not sure what exactly are you referring to, but this patch does not
>>>>>> add new property, it just extends functionality of existing one.
>>>>> Sry, needed to be more specific.
>>>>>
>>>>> You've added  device_set_deferred_probe_reson(dev, &vaf);
>>>>> which expected to be used on every EPROBE_DEFER in dev_err_probe() in
>>>>> combination with
>>>>>
>>>>> +       } else {
>>>>> +               device_set_deferred_probe_reson(dev, &vaf);
>>>>>                   dev_dbg(dev, "error %d: %pV", err, &vaf);
>>>>>
>>>>> ^^ dev_dbg() does not add any runtime overhead during boot unless enabled
>>>>> +       }
>>>>>
>>>>> But:
>>>>>
>>>>> +void device_set_deferred_probe_reson(const struct device *dev, struct
>>>>> va_format *vaf)
>>>>> +{
>>>>> +       const char *drv = dev_driver_string(dev);
>>>>> +
>>>>> +       mutex_lock(&deferred_probe_mutex);
>>>>> +
>>>>> +       kfree(dev->p->deferred_probe_reason);
>>>>> +       dev->p->deferred_probe_reason = kasprintf(GFP_KERNEL, "%s:
>>>>> %pV", drv, vaf);
>>>>> +
>>>>> +       mutex_unlock(&deferred_probe_mutex);
>>>>> +}
>>>>>
>>>>> ^^ Adds locking, kfree() and kasprintf() for every deferred probe
>>>>> during boot and can't be disabled.
>>>>>
>>>>> Right?
>>>> Right, but usually the burden should be insignificant in comparison to
>>>> probe time, so I do not think it is worth optimizing.
>>> I do not think this is going to take. You are suggesting that we
>>> modify pretty much every driver to supply this deferral reason, and I
>>> doubt it will happen. Can we put this burden on providers that raise
>>> the deferral?
>>
>> I wouldn't say they raise the deferral, they just inform resource is not
>> yet available. Only device driver, and only in its probe function can
>> "raise the deferral".
> Well, this is a matter of perspective. If devm_gpiod_get() returns
> -EBUSY and this is returned to driver core, is it GPIO line signals that
> line is busy, or is it the driver applies its knowledge. I say that in
> majority of cases driver does not really get a say in this and simply
> has to pass whatever error condition that is signalled by providers up
> the stack.
>
> I would consider whenever a driver does not propagate -EPROBE_DEFER to
> the driver code a bug that needs fixing, because it should not degrade
> functionality and/or performance just because we have not figured out
> how to order probing properly and have to rely on deferrals.
>
>>
>>>    I.e. majority of code are using devm API now, so we most
>>> likely know the device for which deferral is being raised. We can have
>>> a list of deferral reasons and their devices and when in device code
>>> once probe is done we could try reconciling it with the deferred
>>> devicelist, and this would mean you only need to implement this in
>>> gpiolib, regulator core, clocks core, etc.
>>
>> This patchset tries to solve simple issue - replace multiple lines of
>> code present in multiple probe functions (additionally fixing lot of
>> them) with single call and then enhance it little bit, nothing more.
>>
>> What you are proposing is blurry at the moment for me, provider does not
>> know if consumer want to defer,
> This is my point - the consumer does not get to decide. If deferral is
> raised, it must be honored.
>
>> or will continue working without missing resource,
> Deferral does not mean resource does not exist and the driver has to get
> by if it can. It means the resource is not ready, and even if the system
> can work without it, it will not be working optimally.
>
>> moreover some consumers can acquire resources after probe - again no
>> probe deferral.
> In this case we should not signal deferral either.


But the provider does not know if *get is called in probe context or 
not, so it is not able to differentiate it.

So the whole idea is for me suspicious/wrong. Kind of proof:

1. If you insist that provider's EPROBE_ERROR must be always propagated 
to driver core then.

2. You must enforce that resources can be gathered only from probe.

3. But this is against current practice, even if majority of drivers 
does it from probe, there are many which doesn't.

QED :)


So if you really want to go this way it would be good to look at these 
drivers, check why they do it this way, and try to convert them.

But I do not think it is a good way.


Regards

Andrzej

>
>> Even if it will be done (it can be, for
>> example by creating probe version of all resource get functions), it
>> will require much more changes but finally it will look like:
>>
>> res = devm_get_resource_from_probe(....)
>>
>> if (IS_ERR(res))
>>
>>       return PTR_ERR(res);
>>
>> vs:
>>
>> res = devm_get_resource(...)
>>
>> if (IS_ERR(res))
>>
>>       return dev_err_probe(dev, PTR_ERR(res), ...);
> And we will need to adjust how many hundreds of drivers?
>
> Consider that most drivers use devm_clk_get(), devm_gpiod_get() and
> devm_regulator_get() and their friends. All these APIs already have
> device for which resource is being allocated, and moreover their use
> outside of probe() path is highly suspicious (because devm outside of
> probe() typically result in unwinding in really surprising order). So if
> you could stash device and deferral reason in a list and then scan this
> list in driver core when handling the raised deferral you would not need
> to change anything in individual drivers.

> Hope this clears what I had in mind.
>
> Thanks.
>

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Re: [PATCH v6 2/4] driver core: add deferring probe reason to devices_deferred property

[Mark Brown]

[-- Attachment #1.1: Type: text/plain, Size: 635 bytes --]

On Fri, Jul 10, 2020 at 09:42:49AM +0200, Andrzej Hajda wrote:

> But the provider does not know if *get is called in probe context or 
> not, so it is not able to differentiate it.

> So the whole idea is for me suspicious/wrong. Kind of proof:

> 1. If you insist that provider's EPROBE_ERROR must be always propagated 
> to driver core then.

> 2. You must enforce that resources can be gathered only from probe.

> 3. But this is against current practice, even if majority of drivers 
> does it from probe, there are many which doesn't.

Those drivers are probably buggy anyway at this point given probe
deferral.

[-- Attachment #1.2: signature.asc --]
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[-- Attachment #2: Type: text/plain, Size: 176 bytes --]

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[PATCH v6 3/4] drm/bridge/sii8620: fix resource acquisition error handling

[Andrzej Hajda]

In case of error during resource acquisition driver should print error
message only in case it is not deferred probe, using dev_err_probe helper
solves the issue. Moreover it records defer probe reason for debugging.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
---
 drivers/gpu/drm/bridge/sil-sii8620.c | 21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/bridge/sil-sii8620.c b/drivers/gpu/drm/bridge/sil-sii8620.c
index 92acd336aa89..389c1f029774 100644
--- a/drivers/gpu/drm/bridge/sil-sii8620.c
+++ b/drivers/gpu/drm/bridge/sil-sii8620.c
@@ -2299,10 +2299,9 @@ static int sii8620_probe(struct i2c_client *client,
 	INIT_LIST_HEAD(&ctx->mt_queue);
 
 	ctx->clk_xtal = devm_clk_get(dev, "xtal");
-	if (IS_ERR(ctx->clk_xtal)) {
-		dev_err(dev, "failed to get xtal clock from DT\n");
-		return PTR_ERR(ctx->clk_xtal);
-	}
+	if (IS_ERR(ctx->clk_xtal))
+		return dev_err_probe(dev, PTR_ERR(ctx->clk_xtal),
+				     "failed to get xtal clock from DT\n");
 
 	if (!client->irq) {
 		dev_err(dev, "no irq provided\n");
@@ -2313,16 +2312,14 @@ static int sii8620_probe(struct i2c_client *client,
 					sii8620_irq_thread,
 					IRQF_TRIGGER_HIGH | IRQF_ONESHOT,
 					"sii8620", ctx);
-	if (ret < 0) {
-		dev_err(dev, "failed to install IRQ handler\n");
-		return ret;
-	}
+	if (ret < 0)
+		return dev_err_probe(dev, ret,
+				     "failed to install IRQ handler\n");
 
 	ctx->gpio_reset = devm_gpiod_get(dev, "reset", GPIOD_OUT_HIGH);
-	if (IS_ERR(ctx->gpio_reset)) {
-		dev_err(dev, "failed to get reset gpio from DT\n");
-		return PTR_ERR(ctx->gpio_reset);
-	}
+	if (IS_ERR(ctx->gpio_reset))
+		return dev_err_probe(dev, PTR_ERR(ctx->gpio_reset),
+				     "failed to get reset gpio from DT\n");
 
 	ctx->supplies[0].supply = "cvcc10";
 	ctx->supplies[1].supply = "iovcc18";
-- 
2.17.1


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Re: [PATCH v6 3/4] drm/bridge/sii8620: fix resource acquisition error handling

[Neil Armstrong]

On 26/06/2020 12:01, Andrzej Hajda wrote:
> In case of error during resource acquisition driver should print error
> message only in case it is not deferred probe, using dev_err_probe helper
> solves the issue. Moreover it records defer probe reason for debugging.
> 
> Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
> ---
>  drivers/gpu/drm/bridge/sil-sii8620.c | 21 +++++++++------------
>  1 file changed, 9 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/sil-sii8620.c b/drivers/gpu/drm/bridge/sil-sii8620.c
> index 92acd336aa89..389c1f029774 100644
> --- a/drivers/gpu/drm/bridge/sil-sii8620.c
> +++ b/drivers/gpu/drm/bridge/sil-sii8620.c
> @@ -2299,10 +2299,9 @@ static int sii8620_probe(struct i2c_client *client,
>  	INIT_LIST_HEAD(&ctx->mt_queue);
>  
>  	ctx->clk_xtal = devm_clk_get(dev, "xtal");
> -	if (IS_ERR(ctx->clk_xtal)) {
> -		dev_err(dev, "failed to get xtal clock from DT\n");
> -		return PTR_ERR(ctx->clk_xtal);
> -	}
> +	if (IS_ERR(ctx->clk_xtal))
> +		return dev_err_probe(dev, PTR_ERR(ctx->clk_xtal),
> +				     "failed to get xtal clock from DT\n");
>  
>  	if (!client->irq) {
>  		dev_err(dev, "no irq provided\n");
> @@ -2313,16 +2312,14 @@ static int sii8620_probe(struct i2c_client *client,
>  					sii8620_irq_thread,
>  					IRQF_TRIGGER_HIGH | IRQF_ONESHOT,
>  					"sii8620", ctx);
> -	if (ret < 0) {
> -		dev_err(dev, "failed to install IRQ handler\n");
> -		return ret;
> -	}
> +	if (ret < 0)
> +		return dev_err_probe(dev, ret,
> +				     "failed to install IRQ handler\n");
>  
>  	ctx->gpio_reset = devm_gpiod_get(dev, "reset", GPIOD_OUT_HIGH);
> -	if (IS_ERR(ctx->gpio_reset)) {
> -		dev_err(dev, "failed to get reset gpio from DT\n");
> -		return PTR_ERR(ctx->gpio_reset);
> -	}
> +	if (IS_ERR(ctx->gpio_reset))
> +		return dev_err_probe(dev, PTR_ERR(ctx->gpio_reset),
> +				     "failed to get reset gpio from DT\n");
>  
>  	ctx->supplies[0].supply = "cvcc10";
>  	ctx->supplies[1].supply = "iovcc18";
> 

Nice helper, totally missed this patchset before !

Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>

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[PATCH v6 4/4] drm/bridge: lvds-codec: simplify error handling

[Andrzej Hajda]

Using dev_err_probe code has following advantages:
- shorter code,
- recorded defer probe reason for debugging,
- uniform error code logging.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
---
 drivers/gpu/drm/bridge/lvds-codec.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/bridge/lvds-codec.c b/drivers/gpu/drm/bridge/lvds-codec.c
index 24fb1befdfa2..f19d9f7a5db2 100644
--- a/drivers/gpu/drm/bridge/lvds-codec.c
+++ b/drivers/gpu/drm/bridge/lvds-codec.c
@@ -71,13 +71,9 @@ static int lvds_codec_probe(struct platform_device *pdev)
 	lvds_codec->connector_type = (uintptr_t)of_device_get_match_data(dev);
 	lvds_codec->powerdown_gpio = devm_gpiod_get_optional(dev, "powerdown",
 							     GPIOD_OUT_HIGH);
-	if (IS_ERR(lvds_codec->powerdown_gpio)) {
-		int err = PTR_ERR(lvds_codec->powerdown_gpio);
-
-		if (err != -EPROBE_DEFER)
-			dev_err(dev, "powerdown GPIO failure: %d\n", err);
-		return err;
-	}
+	if (IS_ERR(lvds_codec->powerdown_gpio))
+		return dev_err_probe(dev, PTR_ERR(lvds_codec->powerdown_gpio),
+				     "powerdown GPIO failure\n");
 
 	/* Locate the panel DT node. */
 	panel_node = of_graph_get_remote_node(dev->of_node, 1, 0);
-- 
2.17.1


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Re: [PATCH v6 4/4] drm/bridge: lvds-codec: simplify error handling

[Neil Armstrong]

On 26/06/2020 12:01, Andrzej Hajda wrote:
> Using dev_err_probe code has following advantages:
> - shorter code,
> - recorded defer probe reason for debugging,
> - uniform error code logging.
> 
> Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
> ---
>  drivers/gpu/drm/bridge/lvds-codec.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/lvds-codec.c b/drivers/gpu/drm/bridge/lvds-codec.c
> index 24fb1befdfa2..f19d9f7a5db2 100644
> --- a/drivers/gpu/drm/bridge/lvds-codec.c
> +++ b/drivers/gpu/drm/bridge/lvds-codec.c
> @@ -71,13 +71,9 @@ static int lvds_codec_probe(struct platform_device *pdev)
>  	lvds_codec->connector_type = (uintptr_t)of_device_get_match_data(dev);
>  	lvds_codec->powerdown_gpio = devm_gpiod_get_optional(dev, "powerdown",
>  							     GPIOD_OUT_HIGH);
> -	if (IS_ERR(lvds_codec->powerdown_gpio)) {
> -		int err = PTR_ERR(lvds_codec->powerdown_gpio);
> -
> -		if (err != -EPROBE_DEFER)
> -			dev_err(dev, "powerdown GPIO failure: %d\n", err);
> -		return err;
> -	}
> +	if (IS_ERR(lvds_codec->powerdown_gpio))
> +		return dev_err_probe(dev, PTR_ERR(lvds_codec->powerdown_gpio),
> +				     "powerdown GPIO failure\n");
>  
>  	/* Locate the panel DT node. */
>  	panel_node = of_graph_get_remote_node(dev->of_node, 1, 0);
> 

Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>

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