On 03/20/2012 02:39 AM, Thierry Reding wrote:

* Stephen Warren wrote:

quoted

On 03/14/2012 09:56 AM, Thierry Reding wrote:

quoted

This commit adds very basic support for device tree probing. Currently,
only a PWM and a list of distinct brightness levels can be specified.
Enabling or disabling backlight power via GPIOs is not yet supported.

A pointer to the exit() callback is stored in the driver data to keep it
around until the driver is unloaded.

...

quoted

quoted

 static int pwm_backlight_probe(struct platform_device *pdev)

...

quoted

-	pb->pwm = pwm_request(data->pwm_id, "backlight");
-	if (IS_ERR(pb->pwm)) {
-		dev_err(&pdev->dev, "unable to request PWM for backlight\n");
-		ret = PTR_ERR(pb->pwm);
-		goto err_alloc;
-	} else
-		dev_dbg(&pdev->dev, "got pwm for backlight\n");
+	if (!pb->pwm) {
+		pb->pwm = pwm_request(data->pwm_id, "backlight");
+		if (IS_ERR(pb->pwm)) {
+			dev_err(&pdev->dev, "unable to request PWM for backlight\n");
+			ret = PTR_ERR(pb->pwm);
+			goto err_alloc;
+		} else
+			dev_dbg(&pdev->dev, "got pwm for backlight\n");
+	}

Hmmm. It'd be more consistent if pwm_backlight_parse_dt() called
something like of_pwm_get() instead of of_pwm_request(), so that this
code could always call pwm_request() on the PWM and hence operate the
same irrespective of DT vs non-DT. GPIOs work that way at least.

That's actually what the initial patch had. Unfortunately that's pretty much
the opposite direction of where the PWM framework is headed because it would
involve getting a global index to request the PWM.

Not necessarily; get() could return a controller+index pair, which could
then be passed to request().

I think in the long run it
would be much better to get rid of pwm_request() altogether and unify by
having the non-DT case request the PWM device on a per-chip basis.

That might also work.