Re: [PATCH v2] drm/tinydrm: Move backlight helpers to a separate file

[Noralf Trønnes <noralf@xxxxxxxxxxx>]

Den 26.09.2017 15.06, skrev Noralf Trønnes:
> Den 26.09.2017 13.32, skrev Daniel Vetter:
> > On Tue, Sep 26, 2017 at 04:46:53PM +0530, Meghana Madhyastha wrote:
> > > On Mon, Sep 25, 2017 at 06:31:58PM +0200, Noralf Trønnes wrote:
> > > > Den 25.09.2017 16.56, skrev Noralf Trønnes:
> > > > > Hi Meghana,
> > > > >
> > > > >
> > > > > Den 22.09.2017 17.09, skrev Meghana Madhyastha:
> > > > > > Move backlight helpers from tinydrm-helpers.c to
> > > > > > tinydrm-backlight.c. This is because it is organizationally
> > > > > > simpler to understand and advantageous to group functions
> > > > > > performing a similar function to a separate file as opposed to
> > > > > > having one helper file with heteregenous helper functions.
> > > > > >
> > > > > > Signed-off-by: Meghana Madhyastha <meghana.madhyastha@xxxxxxxxx>
> > > > > > ---
> > > > > I don't think there is much gain in just moving the code like this.
> > > > >
> > > > > The idea is to add a drm_backlight helper that can be useful for all
> > > > > DRM drivers that use the backlight subsystem.
> > > Yes I agree. That definitely makes more sense.
> > > > The full path to that helper would be:
> > > > drivers/gpu/drm/drm_backlight.c
> > > >
> > > > > This is what the TODO says:
> > > > > https://dri.freedesktop.org/docs/drm/gpu/todo.html#tinydrm
> > > > >
> > > > > - backlight helpers, probably best to put them into a new 
> > > > > drm_backlight.c.
> > > > >    This is because drivers/video is de-facto unmaintained. We 
> > > > > could also
> > > > >    move drivers/video/backlight to drivers/gpu/backlight and take 
> > > > > it all
> > > > >    over within drm-misc, but that’s more work.
> > > > >
> > > > > There is also this discussion to take into account:
> > > > > KMS backlight ABI proposition
> > > > > https://lists.freedesktop.org/archives/dri-devel/2017-February/133206.html 
> > > > >
> > > > >
> > > > >
> > > > > I don't remember what came out of that discussion.
> > > > >
> > > > > Noralf.
> > > After having discussed this with Daniel on the #dri-devel irc channel,
> > > here are some of the points suggested.
> > >
> > > Daniel suggested that I first look into the usage of shared backlight
> > > helpers in drm (specifically backlight_update_status to begin with). 
> > > The idea
> > > was to see whether there is any pattern in usage and/or code 
> > > dupication.
> > > If there is, then the next step would be to write helper functions 
> > > which
> > > can be used by other drivers (and not just tinydrm).
> > >
> > > To start with, I went through the instances of backlight_update_status
> > > in the drm code, and made the following observations(most of them are
> > > very simple/naive observations).
> > >
> > > - backlight_update_status is usually called in backlight init (and
> > >    sometimes exit) functions of the drivers just after the device is 
> > > registered.
> > >    So backlight_update_status is called with the registered device 
> > > as the
> > >    parameter.
> > >
> > > Here are the following cases of properties changed/set before
> > > backlight_update_status is called.
> > >
> > > - CASE 1: Brightness is changed (either a macro BRIGHTNESS_MAX_LEVEL 
> > > 100
> > >    is defined or it is manually set) This happens in the following 
> > > files:
> > >
> > >    gma500/cdv_device.c, gma500/mdfld_device.c, 
> > > gma500/oaktrail_device.c,
> > >    gma500/psb_device.c, noveau/noveau_backlight.c(here brightness is 
> > > determined by fuction
> > >    static int nv50_get_intensity)
> > >
> > > - CASE 2: Power property is set (to FB_BLANK_UNBLANK mostly)
> > >    This happens in the following files:
> > >
> > >    omapdrm/displays/panel-dpi.c, panel/panel-innolux-p079zca.c,
> > >    panel/panel-jdi-lt070me05000.c, panel/panel-sharp-lq101r1sx01.c,
> > >    panel/panel-sharp-ls043t1le01.c, tilcdc/tilcdc_panel.c
> > >    - CASE 3: State is set
> > >    This happens in the following files:
> > >
> > >    tinydrm/tinydrm-helpers.c
> > >
> > > - CASE 4: Power and brightness properties are set
> > >    This happens in the following files:
> > >
> > >    atombios_encoders.c, radeon/radeon_legacy_encoders.c,
> > >    shmobile/shmob_drm_backlight.c
> > >
> > > - CASE 5: Power and the state properties are set
> > >    This happens in the following files:
> > >
> > >    panel/panel-lvds.c, panel/panel-panasonic-vvx10f034n00.c,
> > >    panel/panel-simple.c, panel/panel-sitronix-st7789v.c
> > >
> > > Please let me know if I am wrong / missed something. As for next steps,
> > > wouldn't it be an overkill to have a separate helper function for each
> > > of these cases ? Perhaps a generic helper function which would somehow
> > > address these cases would be more appropriate ? Thank you for your
> > > time/patience.
> > I suspect that a lot of these combinations are just plain wrong, but
> > happen to kinda work with the combination of gpu driver and backlight
> > driver they're used on. tbh I have no idea which one is the correct
> > version for enabling a backlight correctly ...
> >
> > So definitely a good task to refactor this into a proper helper, but 
> > looks
> > a lot more involved than at first sight.
>
> Backlight is tricky.
>
> One annoying thing from a DRM point of view is that it's tied to fbdev
> with a notifier fb_notifier_callback() that turns it off on
> FB_EVENT_BLANK and FB_EVENT_CONBLANK. And the logic in that function is
> very convoluted.
>
> And if we look at the gpio backlight driver, we see that there are
> 3 properties that turn off the backlight:
>
> static int gpio_backlight_update_status(struct backlight_device *bl)
> {
>     struct gpio_backlight *gbl = bl_get_data(bl);
>     int brightness = bl->props.brightness;
>
>     if (bl->props.power != FB_BLANK_UNBLANK ||
>         bl->props.fb_blank != FB_BLANK_UNBLANK ||
>         bl->props.state & (BL_CORE_SUSPENDED | BL_CORE_FBBLANK))
>         brightness = 0;
>
>     gpiod_set_value_cansleep(gbl->gpiod, brightness);
>
>     return 0;
> }
>
> This may account for the different ways of controlling backlight in DRM.
>
> Some other aspects:
> - The backlight device has it's own suspend/resume functions.
> - systemd tries to be smart and turn on/off backlight, but that is just
>   annoying with tinydrm drivers that are loaded late since it turns on
>   an uninitialized display. Disabling the service fixes it.

And some more:
The backlight driver is probed before the DRM driver and if DRM should
control backlight, then backlight should be initially off. The pwm_bl
driver has a default-brightness-level property that is set when the
pwm_bl driver probes. If the DRM driver should control backlight, then
this has to be zero/off, or the backlight is turned on before the
display is initialized. So how can we now communicate the default
brightness level to the pwm_bl driver?

The gpio_backlight driver is off by default.

I noticed that backlight is listed under leds in DT bindings now.

> Noralf.
>
> > Do you have any of the hardware supported by any of these drivers? lsmod
> > and then comparing with the modules you're building in your own tree
> > should help you figure this out.
> > -Daniel
> >
> > > -Meghana
> > >
> > > > > > Changes in v2:
> > > > > >    -Improved commit message by explaining why the changes were made.
> > > > > >
> > > > > >    drivers/gpu/drm/tinydrm/core/Makefile            | 2 +-
> > > > > >    drivers/gpu/drm/tinydrm/core/tinydrm-backlight.c | 103
> > > > > > +++++++++++++++++++++++
> > > > > >    drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c   | 94
> > > > > > ---------------------
> > > > > >    drivers/gpu/drm/tinydrm/mi0283qt.c               | 1 +
> > > > > >    drivers/gpu/drm/tinydrm/mipi-dbi.c               | 1 +
> > > > > >    include/drm/tinydrm/tinydrm-backlight.h          | 18 ++++
> > > > > >    6 files changed, 124 insertions(+), 95 deletions(-)
> > > > > >    create mode 100644 
> > > > > > drivers/gpu/drm/tinydrm/core/tinydrm-backlight.c
> > > > > >    create mode 100644 include/drm/tinydrm/tinydrm-backlight.h
> > > > > >
> > > > > > diff --git a/drivers/gpu/drm/tinydrm/core/Makefile
> > > > > > b/drivers/gpu/drm/tinydrm/core/Makefile
> > > > > > index fb221e6..389ca7a 100644
> > > > > > --- a/drivers/gpu/drm/tinydrm/core/Makefile
> > > > > > +++ b/drivers/gpu/drm/tinydrm/core/Makefile
> > > > > > @@ -1,3 +1,3 @@
> > > > > > -tinydrm-y := tinydrm-core.o tinydrm-pipe.o tinydrm-helpers.o
> > > > > > +tinydrm-y := tinydrm-core.o tinydrm-pipe.o tinydrm-backlight.o
> > > > > > tinydrm-helpers.o
> > > > > >      obj-$(CONFIG_DRM_TINYDRM) += tinydrm.o
> > > > > > diff --git a/drivers/gpu/drm/tinydrm/core/tinydrm-backlight.c
> > > > > > b/drivers/gpu/drm/tinydrm/core/tinydrm-backlight.c
> > > > > > new file mode 100644
> > > > > > index 0000000..dc6f17d
> > > > > > --- /dev/null
> > > > > > +++ b/drivers/gpu/drm/tinydrm/core/tinydrm-backlight.c
> > > > > > @@ -0,0 +1,103 @@
> > > > > > +#include <linux/backlight.h>
> > > > > > +#include <linux/dma-buf.h>
> > > > > > +#include <linux/pm.h>
> > > > > > +#include <linux/swab.h>
> > > > > > +
> > > > > > +#include <drm/tinydrm/tinydrm.h>
> > > > > > +#include <drm/tinydrm/tinydrm-backlight.h>
> > > > > > +
> > > > > > +/**
> > > > > > + * 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);
> > > > > > +
> > > > > > +/**
> > > > > > + * tinydrm_enable_backlight - Enable backlight helper
> > > > > > + * @backlight: Backlight device
> > > > > > + *
> > > > > > + * Returns:
> > > > > > + * Zero on success, negative error code on failure.
> > > > > > + */
> > > > > > +int tinydrm_enable_backlight(struct backlight_device *backlight)
> > > > > > +{
> > > > > > +    unsigned int old_state;
> > > > > > +    int ret;
> > > > > > +
> > > > > > +    if (!backlight)
> > > > > > +        return 0;
> > > > > > +
> > > > > > +    old_state = backlight->props.state;
> > > > > > +    backlight->props.state &= ~BL_CORE_FBBLANK;
> > > > > > +    DRM_DEBUG_KMS("Backlight state: 0x%x -> 0x%x\n", old_state,
> > > > > > +              backlight->props.state);
> > > > > > +
> > > > > > +    ret = backlight_update_status(backlight);
> > > > > > +    if (ret)
> > > > > > +        DRM_ERROR("Failed to enable backlight %d\n", ret);
> > > > > > +
> > > > > > +    return ret;
> > > > > > +}
> > > > > > +EXPORT_SYMBOL(tinydrm_enable_backlight);
> > > > > > +
> > > > > > +/**
> > > > > > + * tinydrm_disable_backlight - Disable backlight helper
> > > > > > + * @backlight: Backlight device
> > > > > > + *
> > > > > > + * Returns:
> > > > > > + * Zero on success, negative error code on failure.
> > > > > > + */
> > > > > > +int tinydrm_disable_backlight(struct backlight_device *backlight)
> > > > > > +{
> > > > > > +    unsigned int old_state;
> > > > > > +    int ret;
> > > > > > +
> > > > > > +    if (!backlight)
> > > > > > +        return 0;
> > > > > > +
> > > > > > +    old_state = backlight->props.state;
> > > > > > +    backlight->props.state |= BL_CORE_FBBLANK;
> > > > > > +    DRM_DEBUG_KMS("Backlight state: 0x%x -> 0x%x\n", old_state,
> > > > > > +              backlight->props.state);
> > > > > > +    ret = backlight_update_status(backlight);
> > > > > > +    if (ret)
> > > > > > +        DRM_ERROR("Failed to disable backlight %d\n", ret);
> > > > > > +
> > > > > > +    return ret;
> > > > > > +}
> > > > > > +EXPORT_SYMBOL(tinydrm_disable_backlight);
> > > > > > diff --git a/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c
> > > > > > b/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c
> > > > > > index bd6cce0..ee8ad8c 100644
> > > > > > --- a/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c
> > > > > > +++ b/drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c
> > > > > > @@ -236,100 +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);
> > > > > > -
> > > > > > -/**
> > > > > > - * tinydrm_enable_backlight - Enable backlight helper
> > > > > > - * @backlight: Backlight device
> > > > > > - *
> > > > > > - * Returns:
> > > > > > - * Zero on success, negative error code on failure.
> > > > > > - */
> > > > > > -int tinydrm_enable_backlight(struct backlight_device *backlight)
> > > > > > -{
> > > > > > -    unsigned int old_state;
> > > > > > -    int ret;
> > > > > > -
> > > > > > -    if (!backlight)
> > > > > > -        return 0;
> > > > > > -
> > > > > > -    old_state = backlight->props.state;
> > > > > > -    backlight->props.state &= ~BL_CORE_FBBLANK;
> > > > > > -    DRM_DEBUG_KMS("Backlight state: 0x%x -> 0x%x\n", old_state,
> > > > > > -              backlight->props.state);
> > > > > > -
> > > > > > -    ret = backlight_update_status(backlight);
> > > > > > -    if (ret)
> > > > > > -        DRM_ERROR("Failed to enable backlight %d\n", ret);
> > > > > > -
> > > > > > -    return ret;
> > > > > > -}
> > > > > > -EXPORT_SYMBOL(tinydrm_enable_backlight);
> > > > > > -
> > > > > > -/**
> > > > > > - * tinydrm_disable_backlight - Disable backlight helper
> > > > > > - * @backlight: Backlight device
> > > > > > - *
> > > > > > - * Returns:
> > > > > > - * Zero on success, negative error code on failure.
> > > > > > - */
> > > > > > -int tinydrm_disable_backlight(struct backlight_device *backlight)
> > > > > > -{
> > > > > > -    unsigned int old_state;
> > > > > > -    int ret;
> > > > > > -
> > > > > > -    if (!backlight)
> > > > > > -        return 0;
> > > > > > -
> > > > > > -    old_state = backlight->props.state;
> > > > > > -    backlight->props.state |= BL_CORE_FBBLANK;
> > > > > > -    DRM_DEBUG_KMS("Backlight state: 0x%x -> 0x%x\n", old_state,
> > > > > > -              backlight->props.state);
> > > > > > -    ret = backlight_update_status(backlight);
> > > > > > -    if (ret)
> > > > > > -        DRM_ERROR("Failed to disable backlight %d\n", ret);
> > > > > > -
> > > > > > -    return ret;
> > > > > > -}
> > > > > > -EXPORT_SYMBOL(tinydrm_disable_backlight);
> > > > > >      #if IS_ENABLED(CONFIG_SPI)
> > > > > >    diff --git a/drivers/gpu/drm/tinydrm/mi0283qt.c
> > > > > > b/drivers/gpu/drm/tinydrm/mi0283qt.c
> > > > > > index 7e5bb7d..c161d45 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 <drm/tinydrm/tinydrm-backlight.h>
> > > > > >    #include <linux/delay.h>
> > > > > >    #include <linux/gpio/consumer.h>
> > > > > >    #include <linux/module.h>
> > > > > > diff --git a/drivers/gpu/drm/tinydrm/mipi-dbi.c
> > > > > > b/drivers/gpu/drm/tinydrm/mipi-dbi.c
> > > > > > index 2caeabc..dc84f26 100644
> > > > > > --- a/drivers/gpu/drm/tinydrm/mipi-dbi.c
> > > > > > +++ b/drivers/gpu/drm/tinydrm/mipi-dbi.c
> > > > > > @@ -11,6 +11,7 @@
> > > > > >      #include <drm/tinydrm/mipi-dbi.h>
> > > > > >    #include <drm/tinydrm/tinydrm-helpers.h>
> > > > > > +#include <drm/tinydrm/tinydrm-backlight.h>
> > > > > >    #include <linux/debugfs.h>
> > > > > >    #include <linux/dma-buf.h>
> > > > > >    #include <linux/gpio/consumer.h>
> > > > > > diff --git a/include/drm/tinydrm/tinydrm-backlight.h
> > > > > > b/include/drm/tinydrm/tinydrm-backlight.h
> > > > > > new file mode 100644
> > > > > > index 0000000..6a7b6d5
> > > > > > --- /dev/null
> > > > > > +++ b/include/drm/tinydrm/tinydrm-backlight.h
> > > > > > @@ -0,0 +1,18 @@
> > > > > > +/*
> > > > > > + * Copyright (C) 2016 Noralf Trønnes
> > > > > > + *
> > > > > > + * This program is free software; you can redistribute it and/or 
> > > > > > modify
> > > > > > + * it under the terms of the GNU General Public License as 
> > > > > > published by
> > > > > > + * the Free Software Foundation; either version 2 of the 
> > > > > > License, or
> > > > > > + * (at your option) any later version.
> > > > > > + */
> > > > > > +
> > > > > > +#ifndef __LINUX_TINYDRM_BACKLIGHT_H
> > > > > > +#define __LINUX_TINYDRM_BACKLIGHT_H
> > > > > > +
> > > > > > +struct backlight_device;
> > > > > > +struct backlight_device *tinydrm_of_find_backlight(struct device 
> > > > > > *dev);
> > > > > > +int tinydrm_enable_backlight(struct backlight_device *backlight);
> > > > > > +int tinydrm_disable_backlight(struct backlight_device *backlight);
> > > > > > +
> > > > > > +#endif /* __LINUX_TINYDRM_BACKLIGHT_H */
> > > > > _______________________________________________
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>
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