linux-kernel - How does commit 47ec340c not introduce a bug?

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Message-ID: <20130507091734.GM3658@sgi.com>
Date:	Tue, 7 May 2013 04:17:34 -0500
From:	Robin Holt <holt@....com>
To:	Qing Xu <qingx@...vell.com>,
	Haojian Zhuang <haojian.zhuang@...il.com>,
	Samuel Ortiz <sameo@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: How does commit 47ec340c not introduce a bug?

I noticed a warning while cross-compiling all arm defconfigs.

The mmp2_defconfig gave this warning:

drivers/video/backlight/max8925_bl.c: In function 'max8925_backlight_probe':
drivers/video/backlight/max8925_bl.c:177:3: warning: statement with no effect [-Wunused-value]

This appears to have been introduced by the above commit when !CONFIG_OF

Looking at this more closely, I am not sure how this was ever intended
to be handled or how the errors returned in the CONFIG_OF case were
intended to be handled as the return from max8925_backlight_dt_init is
always ignored.

I think this needs some more attention, but do not feel like I know
enough about it or have any means to test it to weigh in.

Thanks,
Robin


commit 47ec340cb8e232671e7c4a4689ff32c3bdf329da
Author: Qing Xu <qingx@...vell.com>
Date:   Mon Feb 4 23:40:45 2013 +0800

    mfd: max8925: Support dt for backlight
    
    Add device tree support in max8925 backlight.
    
    Signed-off-by: Qing Xu <qingx@...vell.com>
    Signed-off-by: Haojian Zhuang <haojian.zhuang@...il.com>
    Signed-off-by: Samuel Ortiz <sameo@...ux.intel.com>

diff --git a/drivers/video/backlight/max8925_bl.c b/drivers/video/backlight/max8925_bl.c
index 2c9bce0..5ca11b0 100644
--- a/drivers/video/backlight/max8925_bl.c
+++ b/drivers/video/backlight/max8925_bl.c
@@ -101,6 +101,29 @@ static const struct backlight_ops max8925_backlight_ops = {
 	.get_brightness	= max8925_backlight_get_brightness,
 };
 
+#ifdef CONFIG_OF
+static int max8925_backlight_dt_init(struct platform_device *pdev,
+			      struct max8925_backlight_pdata *pdata)
+{
+	struct device_node *nproot = pdev->dev.parent->of_node, *np;
+	int dual_string;
+
+	if (!nproot)
+		return -ENODEV;
+	np = of_find_node_by_name(nproot, "backlight");
+	if (!np) {
+		dev_err(&pdev->dev, "failed to find backlight node\n");
+		return -ENODEV;
+	}
+
+	of_property_read_u32(np, "maxim,max8925-dual-string", &dual_string);
+	pdata->dual_string = dual_string;
+	return 0;
+}
+#else
+#define max8925_backlight_dt_init(x, y)	(-1)
+#endif
+
 static int max8925_backlight_probe(struct platform_device *pdev)
 {
 	struct max8925_chip *chip = dev_get_drvdata(pdev->dev.parent);
@@ -147,6 +170,13 @@ static int max8925_backlight_probe(struct platform_device *pdev)
 	platform_set_drvdata(pdev, bl);
 
 	value = 0;
+	if (pdev->dev.parent->of_node && !pdata) {
+		pdata = devm_kzalloc(&pdev->dev,
+				     sizeof(struct max8925_backlight_pdata),
+				     GFP_KERNEL);
+		max8925_backlight_dt_init(pdev, pdata);
+	}
+
 	if (pdata) {
 		if (pdata->lxw_scl)
 			value |= (1 << 7);
@@ -158,7 +188,6 @@ static int max8925_backlight_probe(struct platform_device *pdev)
 	ret = max8925_set_bits(chip->i2c, data->reg_mode_cntl, 0xfe, value);
 	if (ret < 0)
 		goto out_brt;
-
 	backlight_update_status(bl);
 	return 0;
 out_brt:
--
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