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>

1 files changed, 14 insertions, 0 deletions

diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index 799c4fb4cc2f..a0860b30bd93 100644
--- a/drivers/pwm/core.c
+++ b/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);