linux-kernel - Re: [PATCH] Revert "backlight: pwm: Handle EPROBE

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Date:	Thu, 1 Oct 2015 10:00:22 +0200
From:	Nicolas Ferre <nicolas.ferre@...el.com>
To:	Robert Jarzmik <robert.jarzmik@...e.fr>,
	Thierry Reding <thierry.reding@...il.com>,
	<linux-pwm@...r.kernel.org>,
	Boris BREZILLON <boris.brezillon@...e-electrons.com>,
	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
CC:	Jingoo Han <jingoohan1@...il.com>,
	Lee Jones <lee.jones@...aro.org>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	<linux-fbdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Revert "backlight: pwm: Handle EPROBE_DEFER while
 requesting the PWM"

Le 30/09/2015 21:29, Robert Jarzmik a écrit :
> Robert Jarzmik <robert.jarzmik@...e.fr> writes:
> 
>> This reverts commit 68feaca0b13e453aa14ee064c1736202b48b342f.
>> This commit breaks legacy platforms, for which :
>>  (a) no pwm table is added (legacy platforms)
>>  (b) in this case, in pwm_get(), pmw_lookup_list is empty, and therefore
>>      chosen == NULL, and therefore pwm_get() returns NULL, and pwm_get()
>>      returns -EPROBE_DEFER
>>  (c) as a consequence, this code is unreachable in pwm_bl.c :
>>      if (IS_ERR(pb->pwm)) {
>> 	ret = PTR_ERR(pb->pwm);
>>  	dev_info(&pdev->dev, "%s:%d(): %d\n", __func__, __LINE__, ret);
>>  	if (ret == -EPROBE_DEFER)
>>  		goto err_alloc;
>>
>>  	dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n");
>>  	pb->legacy = true;
>>  	pb->pwm = pwm_request(data->pwm_id, "pwm-backlight");
>>
>> As this code is unreachable, all legacy platforms relying on pwm_id are
>> broken, amongst which pxa have been tested as broken.
>>
>> Signed-off-by: Robert Jarzmik <robert.jarzmik@...e.fr>
> Thierry, would you have a look please ?
> As I said before, all legacy platform relying on pwm_id are broken. I'd like to
> be sure this lands in the next -rc series.

Well, as I answered on the linux-pwm mailing-list (I was not in copy) here:
http://article.gmane.org/gmane.linux.pwm/2744
I wonder if it's not easier to fix the platforms and add the pwm tables...

Otherwise, Boris proposed this fix:
8<-----------------------------------------------------------
diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c
index eff379b..00483d4 100644
--- a/drivers/video/backlight/pwm_bl.c
+++ b/drivers/video/backlight/pwm_bl.c
@@ -273,15 +273,15 @@ static int pwm_backlight_probe(struct platform_device *pdev)
 	pb->pwm = devm_pwm_get(&pdev->dev, NULL);
 	if (IS_ERR(pb->pwm)) {
 		ret = PTR_ERR(pb->pwm);
-		if (ret == -EPROBE_DEFER)
-			goto err_alloc;
 
 		dev_err(&pdev->dev, "unable to request PWM, trying legacy API\n");
 		pb->legacy = true;
 		pb->pwm = pwm_request(data->pwm_id, "pwm-backlight");
 		if (IS_ERR(pb->pwm)) {
 			dev_err(&pdev->dev, "unable to request legacy PWM\n");
-			ret = PTR_ERR(pb->pwm);
+			if (ret != -EPROBE_DEFER)
+				ret = PTR_ERR(pb->pwm);
+
 			goto err_alloc;
 		}
 	}

which is not tested and may add an extra non-valid error log.

Bye,
-- 
Nicolas Ferre
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