Re: [Outreachy kernel] [PATCH v14 2/3] drm/tinydrm: Move tinydrm_of_find_backlight to backlight.c

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On 24/10/17 16:38, Sean Paul wrote:
On Sat, Oct 21, 2017 at 05:27:33PM +0530, Meghana Madhyastha wrote:
Rename tinydrm_of_find_backlight to of_find_backlight and move
it to linux/backlight.c so that it can be used by other drivers.

Signed-off-by: Meghana Madhyastha <meghana.madhyastha@xxxxxxxxx>
---
Changes in v14:
  -s/backlight_get/of_find_backlight/

  drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c | 40 --------------------------
  drivers/gpu/drm/tinydrm/mi0283qt.c             |  3 +-
  drivers/video/backlight/backlight.c            | 37 ++++++++++++++++++++++++
  include/drm/tinydrm/tinydrm-helpers.h          |  2 --
  include/linux/backlight.h                      | 19 ++++++++++++
  5 files changed, 58 insertions(+), 43 deletions(-)

diff --git a/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c b/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c
index a42dee6..cb1a01a 100644
--- a/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c
+++ b/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c
@@ -236,46 +236,6 @@ void tinydrm_xrgb8888_to_gray8(u8 *dst, void *vaddr, struct drm_framebuffer *fb,
  }
  EXPORT_SYMBOL(tinydrm_xrgb8888_to_gray8);
-/**
- * tinydrm_of_find_backlight - Find backlight device in device-tree
- * @dev: Device
- *
- * This function looks for a DT node pointed to by a property named 'backlight'
- * and uses of_find_backlight_by_node() to get the backlight device.
- * Additionally if the brightness property is zero, it is set to
- * max_brightness.
- *
- * Returns:
- * NULL if there's no backlight property.
- * Error pointer -EPROBE_DEFER if the DT node is found, but no backlight device
- * is found.
- * If the backlight device is found, a pointer to the structure is returned.
- */
-struct backlight_device *tinydrm_of_find_backlight(struct device *dev)
-{
-	struct backlight_device *backlight;
-	struct device_node *np;
-
-	np = of_parse_phandle(dev->of_node, "backlight", 0);
-	if (!np)
-		return NULL;
-
-	backlight = of_find_backlight_by_node(np);
-	of_node_put(np);
-
-	if (!backlight)
-		return ERR_PTR(-EPROBE_DEFER);
-
-	if (!backlight->props.brightness) {
-		backlight->props.brightness = backlight->props.max_brightness;
-		DRM_DEBUG_KMS("Backlight brightness set to %d\n",
-			      backlight->props.brightness);
-	}
-
-	return backlight;
-}
-EXPORT_SYMBOL(tinydrm_of_find_backlight);
-
  #if IS_ENABLED(CONFIG_SPI)
/**
diff --git a/drivers/gpu/drm/tinydrm/mi0283qt.c b/drivers/gpu/drm/tinydrm/mi0283qt.c
index 7fd2691..53ab5a0 100644
--- a/drivers/gpu/drm/tinydrm/mi0283qt.c
+++ b/drivers/gpu/drm/tinydrm/mi0283qt.c
@@ -12,6 +12,7 @@
  #include <drm/tinydrm/ili9341.h>
  #include <drm/tinydrm/mipi-dbi.h>
  #include <drm/tinydrm/tinydrm-helpers.h>
+#include <linux/backlight.h>
  #include <linux/delay.h>
  #include <linux/gpio/consumer.h>
  #include <linux/module.h>
@@ -188,7 +189,7 @@ static int mi0283qt_probe(struct spi_device *spi)
  	if (IS_ERR(mipi->regulator))
  		return PTR_ERR(mipi->regulator);
- mipi->backlight = tinydrm_of_find_backlight(dev);
+	mipi->backlight = of_find_backlight(dev);
  	if (IS_ERR(mipi->backlight))
  		return PTR_ERR(mipi->backlight);
diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
index 8049e76..76d46c3 100644
--- a/drivers/video/backlight/backlight.c
+++ b/drivers/video/backlight/backlight.c
@@ -580,6 +580,43 @@ struct backlight_device *of_find_backlight_by_node(struct device_node *node)
  EXPORT_SYMBOL(of_find_backlight_by_node);
  #endif
+/**
+ * of_find_backlight - Get backlight device
+ * @dev: Device
+ *
+ * This function looks for a property named 'backlight' on the DT node
+ * connected to @dev and looks up the backlight device.
+ *
+ * Call backlight_put() to drop the reference on the backlight device.
+ *
+ * Returns:
+ * A pointer to the backlight device if found.
+ * Error pointer -EPROBE_DEFER if the DT property is set, but no backlight
+ * device is found.
+ * NULL if there's no backlight property.
+ */
+struct backlight_device *of_find_backlight(struct device *dev)
+{
+	struct backlight_device *bd = NULL;
+	struct device_node *np;
+
+	if (!dev)
+		return NULL;
+
+	if (IS_ENABLED(CONFIG_OF) && dev->of_node) {
+		np = of_parse_phandle(dev->of_node, "backlight", 0);
+		if (np) {
+			bd = of_find_backlight_by_node(np);
+			of_node_put(np);
+			if (!bd)
+				return ERR_PTR(-EPROBE_DEFER);
+		}
+	}
+
+	return bd;
+}
+EXPORT_SYMBOL(of_find_backlight);
+
  static void __exit backlight_class_exit(void)
  {
  	class_destroy(backlight_class);
diff --git a/include/drm/tinydrm/tinydrm-helpers.h b/include/drm/tinydrm/tinydrm-helpers.h
index f54fae0..0a4ddbc 100644
--- a/include/drm/tinydrm/tinydrm-helpers.h
+++ b/include/drm/tinydrm/tinydrm-helpers.h
@@ -46,8 +46,6 @@ void tinydrm_xrgb8888_to_rgb565(u16 *dst, void *vaddr,
  void tinydrm_xrgb8888_to_gray8(u8 *dst, void *vaddr, struct drm_framebuffer *fb,
  			       struct drm_clip_rect *clip);
-struct backlight_device *tinydrm_of_find_backlight(struct device *dev);
-
  size_t tinydrm_spi_max_transfer_size(struct spi_device *spi, size_t max_len);
  bool tinydrm_spi_bpw_supported(struct spi_device *spi, u8 bpw);
  int tinydrm_spi_transfer(struct spi_device *spi, u32 speed_hz,
diff --git a/include/linux/backlight.h b/include/linux/backlight.h
index b88fabb..f98b684 100644
--- a/include/linux/backlight.h
+++ b/include/linux/backlight.h
@@ -159,6 +159,16 @@ static inline int backlight_disable(struct backlight_device *bd)
  	return backlight_update_status(bd);
  }
+/**
+ * backlight_put - Drop backlight reference
+ * @bd: the backlight device to put
+ */
+static inline void backlight_put(struct backlight_device *bd)
+{
+	if (bd)
+		put_device(&bd->dev);
+}


As I mentioned in my last review, I don't think we need this function.

Just to check... some DRM drivers do allow themselves to work if CONFIG_BACKLIGHT_CLASS_DEVICE isn't enabled (as discussed earlier in the thread ;-). Did you consider what happens when this happens.

Wrapped up with backlight_put() we are sure never to accidentally dereference bd in DRM de-init paths when CONFIG_BACKLIGHT_CLASS_DEVICVE if it is not set. With a raw put_device() all that conditional logic ends up on the driver.


Daniel.


+
  extern struct backlight_device *backlight_device_register(const char *name,
  	struct device *dev, void *devdata, const struct backlight_ops *ops,
  	const struct backlight_properties *props);
@@ -202,4 +212,13 @@ of_find_backlight_by_node(struct device_node *node)
  }
  #endif
+#if IS_ENABLED(CONFIG_BACKLIGHT_CLASS_DEVICE)
+struct backlight_device *of_find_backlight(struct device *dev);
+#else
+static inline struct backlight_device *of_find_backlight(struct device *dev)
+{
+	return NULL;
+}
+#endif
+
  #endif
--
2.7.4

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