On Tue, Oct 24, 2017 at 04:56:59PM +0100, Daniel Thompson wrote:
> 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.
>
Thanks for pointing that out, definitely a fair point.
I don't really mind putting the NULL check in the driver code. The return
values of of_find_backlight are well documented, so it shouldn't be too much
of a problem.
That said, this is your rodeo, so if you prefer to supply the put helper, that's
A-Ok with me.
Sean
>
> 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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> > > To view this discussion on the web visit https://groups.google.com/d/msgid/outreachy-kernel/678c3adb07b729acf6e80119ab9adec01d89842f.1508586429.git.meghana.madhyastha%40gmail.com.
> > > For more options, visit https://groups.google.com/d/optout.
> >
>
--
Sean Paul, Software Engineer, Google / Chromium OS
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