pwm: Try to load modules during pwm_get()

Add a module name string to the pwm_lookup struct and if specified try
to load the module using request_module() if pwmchip_find_by_name() is
unable to find the PWM chip.

This is a last resort to work around drivers that can't - and can't be
made to - deal with deferred probe.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
[thierry.reding@gmail.com: rename new macro, reword commit message]
[thierry.reding@gmail.com: add comment explaining use-case]
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/core.c

@@ -765,6 +765,7 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
 	unsigned int best = 0;
 	struct pwm_lookup *p, *chosen = NULL;
 	unsigned int match;
+	int err;
 
 	/* look up via DT first */
 	if (IS_ENABLED(CONFIG_OF) && dev && dev->of_node)
@@ -825,6 +826,19 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
 		return ERR_PTR(-ENODEV);
 
 	chip = pwmchip_find_by_name(chosen->provider);
+
+	/*
+	 * If the lookup entry specifies a module, load the module and retry
+	 * the PWM chip lookup. This can be used to work around driver load
+	 * ordering issues if driver's can't be made to properly support the
+	 * deferred probe mechanism.
+	 */
+	if (!chip && chosen->module) {
+		err = request_module(chosen->module);
+		if (err == 0)
+			chip = pwmchip_find_by_name(chosen->provider);
+	}
+
 	if (!chip)
 		return ERR_PTR(-EPROBE_DEFER);
 

include/linux/pwm.h

@@ -603,18 +603,25 @@ struct pwm_lookup {
 	const char *con_id;
 	unsigned int period;
 	enum pwm_polarity polarity;
+	const char *module; /* optional, may be NULL */
 };
 
-#define PWM_LOOKUP(_provider, _index, _dev_id, _con_id, _period, _polarity) \
+#define PWM_LOOKUP_WITH_MODULE(_provider, _index, _dev_id, _con_id,	\
+			       _period, _polarity, _module)		\
 	{								\
 		.provider = _provider,					\
 		.index = _index,					\
 		.dev_id = _dev_id,					\
 		.con_id = _con_id,					\
 		.period = _period,					\
-		.polarity = _polarity			\
+		.polarity = _polarity,					\
+		.module = _module,					\
 	}
 
+#define PWM_LOOKUP(_provider, _index, _dev_id, _con_id, _period, _polarity) \
+	PWM_LOOKUP_WITH_MODULE(_provider, _index, _dev_id, _con_id, _period, \
+			       _polarity, NULL)
+
 #if IS_ENABLED(CONFIG_PWM)
 void pwm_add_table(struct pwm_lookup *table, size_t num);
 void pwm_remove_table(struct pwm_lookup *table, size_t num);