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SubjectRE: [PATCH] FB: add early fb blank feature.
Date
Hi, Lars-Peter Clausen.

> > Why do we need a new notifier chain? Can't we introduce a new event for
> > the
> > existing chain?

Yes, it's good point. I will consider a new event as you said. thank you for
your advice. :)


> -----Original Message-----
> From: Inki Dae [mailto:inki.dae@samsung.com]
> Sent: Monday, September 26, 2011 7:37 PM
> To: 'Lars-Peter Clausen'
> Cc: 'FlorianSchandinat@gmx.de'; 'linux-fbdev@vger.kernel.org';
> 'akpm@linux-foundation.org'; 'linux-kernel@vger.kernel.org';
> 'kyungmin.park@samsung.com'
> Subject: RE: [PATCH] FB: add early fb blank feature.
>
> Hi, Lars-Peter Clausen.
>
> Sorry for being late.
>
> > -----Original Message-----
> > From: Lars-Peter Clausen [mailto:lars@metafoo.de]
> > Sent: Thursday, September 15, 2011 8:37 PM
> > To: Inki Dae
> > Cc: FlorianSchandinat@gmx.de; linux-fbdev@vger.kernel.org; akpm@linux-
> > foundation.org; linux-kernel@vger.kernel.org; kyungmin.park@samsung.com
> > Subject: Re: [PATCH] FB: add early fb blank feature.
> >
> > Hi
> >
> > I have a LCD panel with an similar issue, and I think the idea to
> > introduce a
> > early fb blank event is the right solution. I have some comments and
> > questions
> > on this particular implementation though.
> >
> > On 09/09/2011 07:03 AM, Inki Dae wrote:
> > > this patch adds early fb blank feature that this is a callback of
> > > lcd panel driver would be called prior to fb driver's one.
> > > in case of MIPI-DSI based video mode LCD Panel, for lcd power off,
> > > the power off commands should be transferred to lcd panel with display
> > > and mipi-dsi controller enabled because the commands is set to lcd
> panel
> > > at vsync porch period. on the other hand, in opposite case, the
> callback
> > > of fb driver should be called prior to lcd panel driver's one because
> of
> > > same issue. now we could handle call order to fb blank properly.
> > >
> > > the order is as the following:
> > >
> > > at fb_blank function of fbmem.c
> > > -> fb_early_notifier_call_chain()
> > > -> lcd panel driver's early_set_power()
> > > -> info->fbops->fb_blank()
> > > -> fb driver's fb_blank()
> > > -> fb_notifier_call_chain()
> > > -> lcd panel driver's set_power()
> > >
> >
> > I wonder if we really need the lcd_ops early_set_power callback. I can't
> > really
> > imagine a situation where you need to power the LCD down only after the
> > LCD
> > controller has been shutdown.
> >
>
> if fb_blank mode is changed to FB_BLANK_POWERDOWN then display controller
> would be off(clock disable). On the other hand, lcd panel would be still
> on. at this time, you could see some issue like sparkling on lcd panel
> because video clock to be delivered to ldi module of lcd panel was
> disabled.
>
> > So I wonder if we couldn't just have the set_power callback, but listen
> to
> > both
> > events and call set_power for early blank events with code !=
> > FB_BLANK_UNBLANK
> > and for normal blank events with code == FB_BLANK_UNBLANK?
> >
>
> with this feaure, if a event is FB_BLANK_POWERDOWN then early_set_power()
> callback would be called for lcd panel to be off and if FB_BLANK_UNBLANK
> or FB_BLANK_NORMAL then set_power() callback would be called for lcd panel
> to be on.
>
> > > note that early fb blank mode is valid only if lcd_ops-
> >early_blank_mode
> > is 1.
> > > if the value is 0 then early fb blank callback would be ignored.
> > >
> > > this patch is based on git repository below:
> > > git://github.com/schandinat/linux-2.6.git
> > > branch: fbdev-next
> > > commit-id: a67472ad1ae040f073e45048cbc5a01195f2e3f5
> > >
> > > Signed-off-by: Inki Dae <inki.dae@samsung.com>
> > > Signed-off-by: KyungMin Park <kyungmin.park@samsung.com>
> > > ---
> > > drivers/video/backlight/lcd.c | 77
> > ++++++++++++++++++++++++++++++++++++++--
> > > drivers/video/fb_notify.c | 31 ++++++++++++++++
> > > drivers/video/fbmem.c | 25 +++++++------
> > > include/linux/fb.h | 4 ++
> > > include/linux/lcd.h | 61 ++++++++++++++++++++++++--------
> >
> > In my opinion this should be split into two patches, one adding the
> early
> > blank
> > event, one adding support for it to the LCD framework.
> >
>
> You are right. this patch should be split into two patches. Thank you.
>
> > > 5 files changed, 167 insertions(+), 31 deletions(-)
> > >
> > > [...]
> > > diff --git a/drivers/video/fb_notify.c b/drivers/video/fb_notify.c
> > > index 8c02038..3930c7c 100644
> > > --- a/drivers/video/fb_notify.c
> > > +++ b/drivers/video/fb_notify.c
> > > @@ -13,9 +13,20 @@
> > > #include <linux/fb.h>
> > > #include <linux/notifier.h>
> > >
> > > +static BLOCKING_NOTIFIER_HEAD(fb_early_notifier_list);
> > > static BLOCKING_NOTIFIER_HEAD(fb_notifier_list);
> > >
> > > /**
> > > + * fb_register_early_client - register a client early notifier
> > > + * @nb: notifier block to callback on events
> > > + */
> > > +int fb_register_early_client(struct notifier_block *nb)
> > > +{
> > > + return blocking_notifier_chain_register(&fb_early_notifier_list,
> > nb);
> > > +}
> > > +EXPORT_SYMBOL(fb_register_early_client);
> > > +
> >
> > Why do we need a new notifier chain? Can't we introduce a new event for
> > the
> > existing chain?
> >
>
> Suppose that we have only fb_notifier_list. Once lcd_device_register() is
> called by lcd panel driver, existing two notifiers would be added
> fb_notifier_list and when fb_blank is called by user process, some
> callback registered to the fb_notifier_list would be called two times, one
> is set_power() and another one is early_set_power(). as you know, this is
> not the thing we want. If there is any missing point, please give me your
> comment.
>
>
> > > +/**
> > > * fb_register_client - register a client notifier
> > > * @nb: notifier block to callback on events
> > > */
> > > @@ -26,6 +37,16 @@ int fb_register_client(struct notifier_block *nb)
> > > EXPORT_SYMBOL(fb_register_client);
> > >
> > > /**
> > > + * fb_unregister_early_client - unregister a client early
> notifier
> > > + * @nb: notifier block to callback on events
> > > + */
> > > +int fb_unregister_early_client(struct notifier_block *nb)
> > > +{
> > > + return blocking_notifier_chain_unregister(&fb_early_notifier_list,
> > nb);
> > > +}
> > > +EXPORT_SYMBOL(fb_unregister_early_client);
> > > +
> > > +/**
> > > * fb_unregister_client - unregister a client notifier
> > > * @nb: notifier block to callback on events
> > > */
> > > @@ -36,6 +57,16 @@ int fb_unregister_client(struct notifier_block *nb)
> > > EXPORT_SYMBOL(fb_unregister_client);
> > >
> > > /**
> > > + * fb_early_notifier_call_chain - early notify clients of fb_events
> > > + *
> > > + */
> > > +int fb_early_notifier_call_chain(unsigned long val, void *v)
> > > +{
> > > + return blocking_notifier_call_chain(&fb_early_notifier_list, val,
> > v);
> > > +}
> > > +EXPORT_SYMBOL_GPL(fb_early_notifier_call_chain);
> > > +
> > > +/**
> > > * fb_notifier_call_chain - notify clients of fb_events
> > > *
> > > */
> > > diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
> > > index ad93629..cf22516 100644
> > > --- a/drivers/video/fbmem.c
> > > +++ b/drivers/video/fbmem.c
> > > @@ -1031,24 +1031,25 @@ fb_set_var(struct fb_info *info, struct
> > fb_var_screeninfo *var)
> > >
> > > int
> > > fb_blank(struct fb_info *info, int blank)
> > > -{
> > > - int ret = -EINVAL;
> > > +{
> > > + struct fb_event event;
> > > + int ret = -EINVAL;
> > >
> > > - if (blank > FB_BLANK_POWERDOWN)
> > > - blank = FB_BLANK_POWERDOWN;
> > > + if (blank > FB_BLANK_POWERDOWN)
> > > + blank = FB_BLANK_POWERDOWN;
> > >
> > > - if (info->fbops->fb_blank)
> > > - ret = info->fbops->fb_blank(blank, info);
> > > + event.info = info;
> > > + event.data = &blank;
> > >
> > > - if (!ret) {
> > > - struct fb_event event;
> > > + fb_early_notifier_call_chain(FB_EVENT_BLANK, &event);
> > >
> > > - event.info = info;
> > > - event.data = &blank;
> > > + if (info->fbops->fb_blank)
> > > + ret = info->fbops->fb_blank(blank, info);
> >
> > I think we have to handle the case where the fb_blank callback fails and
> > should
> > somehow revert the effects of the early blank event.
> >
>
> You are right. it should be reverted with fail. thank you.
>
> >
> > > +
> > > + if (!ret)
> > > fb_notifier_call_chain(FB_EVENT_BLANK, &event);
> > > - }
> > >
> >
> >
> >
> > > - return ret;
> > > + return ret;
> > > }
> > >
> > > static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
> > > diff --git a/include/linux/fb.h b/include/linux/fb.h
> > > index 1d6836c..1d7d995 100644
> > > --- a/include/linux/fb.h
> > > +++ b/include/linux/fb.h
> > > @@ -562,6 +562,10 @@ struct fb_blit_caps {
> > > u32 flags;
> > > };
> > >
> > > +extern int fb_register_early_client(struct notifier_block *nb);
> > > +extern int fb_unregister_early_client(struct notifier_block *nb);
> > > +extern int fb_early_notifier_call_chain(unsigned long val, void *v);
> > > +
> > > extern int fb_register_client(struct notifier_block *nb);
> > > extern int fb_unregister_client(struct notifier_block *nb);
> > > extern int fb_notifier_call_chain(unsigned long val, void *v);
> > > diff --git a/include/linux/lcd.h b/include/linux/lcd.h
> > > index 8877123..930d1cc 100644
> > > --- a/include/linux/lcd.h
> > > +++ b/include/linux/lcd.h
> > > @@ -37,10 +37,21 @@ struct lcd_properties {
> > > };
> > >
> > > struct lcd_ops {
> > > - /* Get the LCD panel power status (0: full on, 1..3: controller
> > > - power on, flat panel power off, 4: full off), see FB_BLANK_XXX */
> > > + /*
> > > + * Get the LCD panel power status (0: full on, 1..3: controller
> > > + * power on, flat panel power off, 4: full off), see FB_BLANK_XXX
> > > + */
> > > int (*get_power)(struct lcd_device *);
> > > - /* Enable or disable power to the LCD (0: on; 4: off, see
> > FB_BLANK_XXX) */
> > > + /*
> > > + * Get the current contrast setting (0-max_contrast) and
> >
> > ???
> >
>
> Ah, I missed it. this is a comment wrong so I will remove it. thank you.
>
> > > + * Enable or disable power to the LCD (0: on; 4: off, see
> > FB_BLANK_XXX)
> > > + * this callback would be called proir to fb driver's fb_blank
> > callback.
> > > + */
> > > + int (*early_set_power)(struct lcd_device *, int power);
> > > + /*
> > > + * Get the current contrast setting (0-max_contrast)
> > > + * Enable or disable power to the LCD (0: on; 4: off, see
> > FB_BLANK_XXX)
> > > + */
> > > int (*set_power)(struct lcd_device *, int power);
> > > /* Get the current contrast setting (0-max_contrast) */
> > > int (*get_contrast)(struct lcd_device *);
> > > @@ -48,21 +59,35 @@ struct lcd_ops {
> > > int (*set_contrast)(struct lcd_device *, int contrast);
> > > /* Set LCD panel mode (resolutions ...) */
> > > int (*set_mode)(struct lcd_device *, struct fb_videomode *);
> > > - /* Check if given framebuffer device is the one LCD is bound to;
> > > - return 0 if not, !=0 if it is. If NULL, lcd always matches the
fb.
> > */
> > > + /*
> > > + * Check if given framebuffer device is the one LCD is bound to;
> > > + * return 0 if not, !=0 if it is. If NULL, lcd always matches the
> > fb.
> > > + */
> > > int (*check_fb)(struct lcd_device *, struct fb_info *);
> > > +
> > > + /*
> > > + * indicate whether enabling early blank mode or not.
> > > + * (0: disable; 1: enable);
> > > + * if enabled, lcd blank callback would be called prior
> > > + * to fb blank callback.
> > > + */
> > > + unsigned int early_blank_mode;
> >
> > I think it should be sufficient to check early_set_power for NULL
> instead
> > of
> > adding this additional flag.
> >
>
> You are right. I will modify it. thank you.
>
> > > };
> > >
> > > struct lcd_device {
> > > struct lcd_properties props;
> > > - /* This protects the 'ops' field. If 'ops' is NULL, the driver that
> > > - registered this device has been unloaded, and if
> > class_get_devdata()
> > > - points to something in the body of that driver, it is also
> > invalid. */
> > > + /*
> > > + * This protects the 'ops' field. If 'ops' is NULL, the driver that
> > > + * registered this device has been unloaded, and if
> > class_get_devdata()
> > > + * points to something in the body of that driver, it is also
> > invalid.
> > > + */
> > > struct mutex ops_lock;
> > > /* If this is NULL, the backing module is unloaded */
> > > struct lcd_ops *ops;
> > > /* Serialise access to set_power method */
> > > struct mutex update_lock;
> > > + /* The framebuffer early notifier block */
> > > + struct notifier_block fb_early_notif;
> > > /* The framebuffer notifier block */
> > > struct notifier_block fb_notif;
> > >
> > > @@ -72,16 +97,22 @@ struct lcd_device {
> > > struct lcd_platform_data {
> > > /* reset lcd panel device. */
> > > int (*reset)(struct lcd_device *ld);
> > > - /* on or off to lcd panel. if 'enable' is 0 then
> > > - lcd power off and 1, lcd power on. */
> > > + /*
> > > + * on or off to lcd panel. if 'enable' is 0 then
> > > + * lcd power off and 1, lcd power on.
> > > + */
> > > int (*power_on)(struct lcd_device *ld, int enable);
> > >
> > > - /* it indicates whether lcd panel was enabled
> > > - from bootloader or not. */
> > > + /*
> > > + * it indicates whether lcd panel was enabled
> > > + * from bootloader or not.
> > > + */
> > > int lcd_enabled;
> > > - /* it means delay for stable time when it becomes low to high
> > > - or high to low that is dependent on whether reset gpio is
> > > - low active or high active. */
> > > + /*
> > > + * it means delay for stable time when it becomes low to high
> > > + * or high to low that is dependent on whether reset gpio is
> > > + * low active or high active.
> > > + */
> >
> > The formatting cleanup patches should go into a separate patch.
>
> Ok, get it. and I will re-send this patch. thank you again. :)



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