[PATCH 0/2] Allow disabling all native fbdev drivers and only keeping DRM emulation

[PATCH 0/2] Allow disabling all native fbdev drivers and only keeping DRM emulation

[Javier Martinez Canillas]

This patch series splits the fbdev core support in two different Kconfig
symbols: FB and FB_CORE. The motivation for this is to allow CONFIG_FB to
be disabled, while still having the the core fbdev support needed for the
CONFIG_DRM_FBDEV_EMULATION to be enabled. The motivation is automatically
disabling all fbdev drivers instead of having to be disabled individually.

The reason for doing this is that now with simpledrm, there's no need for
the legacy fbdev (e.g: efifb or vesafb) drivers anymore and many distros
now disable them. But it would simplify the config a lot fo have a single
Kconfig symbol to disable all fbdev drivers.

I've build tested with possible combinations of CONFIG_FB, CONFIG_FB_CORE,
CONFIG_DRM_FBDEV_EMULATION and CONFIG_FB_DEVICE symbols set to 'y' or 'n'.

Patch 1/2 makes the CONFIG_FB split that is mentioned above and patch 2/2
makes DRM fbdev emulation depend on the new FB_CORE symbol instead of FB.


Javier Martinez Canillas (2):
  fbdev: Split frame buffer support in FB and FB_CORE symbols
  drm: Make fbdev emulation depend on FB_CORE instead of FB

 arch/x86/Makefile                 |  2 +-
 arch/x86/video/Makefile           |  2 +-
 drivers/gpu/drm/Kconfig           |  2 +-
 drivers/video/console/Kconfig     |  2 +-
 drivers/video/fbdev/Kconfig       | 62 ++++++++++++++++++-------------
 drivers/video/fbdev/core/Makefile | 14 +++----
 6 files changed, 48 insertions(+), 36 deletions(-)

-- 
2.41.0

[PATCH 1/2] fbdev: Split frame buffer support in FB and FB_CORE symbols

[Javier Martinez Canillas]

Currently the CONFIG_FB option has to be enabled even if no legacy fbdev
drivers are needed (e.g: only to have support for framebuffer consoles).

The DRM subsystem has a fbdev emulation layer, but depends on CONFIG_FB
and so it can only be enabled if that dependency is enabled as well.

That means fbdev drivers have to be explicitly disabled if users want to
enable CONFIG_FB, only to use fbcon and/or the DRM fbdev emulation layer.

This patch introduces a CONFIG_FB_CORE option that could be enabled just
to have the core support needed for CONFIG_DRM_FBDEV_EMULATION, allowing
CONFIG_FB to be disabled (and automatically disabling all fbdev drivers).

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
---

 arch/x86/Makefile                 |  2 +-
 arch/x86/video/Makefile           |  2 +-
 drivers/video/console/Kconfig     |  2 +-
 drivers/video/fbdev/Kconfig       | 62 ++++++++++++++++++-------------
 drivers/video/fbdev/core/Makefile | 14 +++----
 5 files changed, 47 insertions(+), 35 deletions(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index b39975977c03..89a02e69be5f 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -259,7 +259,7 @@ drivers-$(CONFIG_PCI)            += arch/x86/pci/
 # suspend and hibernation support
 drivers-$(CONFIG_PM) += arch/x86/power/
 
-drivers-$(CONFIG_FB) += arch/x86/video/
+drivers-$(CONFIG_FB_CORE) += arch/x86/video/
 
 ####
 # boot loader support. Several targets are kept for legacy purposes
diff --git a/arch/x86/video/Makefile b/arch/x86/video/Makefile
index 11640c116115..5ebe48752ffc 100644
--- a/arch/x86/video/Makefile
+++ b/arch/x86/video/Makefile
@@ -1,2 +1,2 @@
 # SPDX-License-Identifier: GPL-2.0-only
-obj-$(CONFIG_FB)               += fbdev.o
+obj-$(CONFIG_FB_CORE)		+= fbdev.o
diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
index a2a88d42edf0..1b5a319971ed 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig
@@ -72,7 +72,7 @@ config DUMMY_CONSOLE_ROWS
 
 config FRAMEBUFFER_CONSOLE
 	bool "Framebuffer Console support"
-	depends on FB && !UML
+	depends on FB_CORE && !UML
 	select VT_HW_CONSOLE_BINDING
 	select CRC32
 	select FONT_SUPPORT
diff --git a/drivers/video/fbdev/Kconfig b/drivers/video/fbdev/Kconfig
index cecf15418632..74d7a305657a 100644
--- a/drivers/video/fbdev/Kconfig
+++ b/drivers/video/fbdev/Kconfig
@@ -6,10 +6,8 @@
 config FB_NOTIFY
 	bool
 
-menuconfig FB
-	tristate "Support for frame buffer devices"
-	select FB_NOTIFY
-	select VIDEO_CMDLINE
+menuconfig FB_CORE
+	tristate "Core support for frame buffer devices"
 	help
 	  The frame buffer device provides an abstraction for the graphics
 	  hardware. It represents the frame buffer of some video hardware and
@@ -33,6 +31,20 @@ menuconfig FB
 	  <http://www.munted.org.uk/programming/Framebuffer-HOWTO-1.3.html> for more
 	  information.
 
+	  This options enables the core support for frame buffer devices.
+
+menuconfig FB
+	tristate "Support for frame buffer device drivers"
+	depends on FB_CORE
+	select FB_NOTIFY
+	select VIDEO_CMDLINE
+	help
+	  This enables support for native frame buffer device (fbdev) drivers.
+
+	  The DRM subsystem provides support for emulated frame buffer devices
+	  on top of KMS drivers, but this option allows legacy fbdev drivers to
+	  be enabled as well.
+
 	  Say Y here and to the driver for your graphics board below if you
 	  are compiling a kernel for a non-x86 architecture.
 
@@ -44,7 +56,7 @@ menuconfig FB
 
 config FIRMWARE_EDID
 	bool "Enable firmware EDID"
-	depends on FB
+	depends on FB_CORE
 	help
 	  This enables access to the EDID transferred from the firmware.
 	  On the i386, this is from the Video BIOS. Enable this if DDC/I2C
@@ -59,7 +71,7 @@ config FIRMWARE_EDID
 
 config FB_DEVICE
 	bool "Provide legacy /dev/fb* device"
-	depends on FB
+	depends on FB_CORE
 	default y
 	help
 	  Say Y here if you want the legacy /dev/fb* device file and
@@ -69,13 +81,13 @@ config FB_DEVICE
 
 config FB_DDC
 	tristate
-	depends on FB
+	depends on FB_CORE
 	select I2C_ALGOBIT
 	select I2C
 
 config FB_CFB_FILLRECT
 	tristate
-	depends on FB
+	depends on FB_CORE
 	help
 	  Include the cfb_fillrect function for generic software rectangle
 	  filling. This is used by drivers that don't provide their own
@@ -83,7 +95,7 @@ config FB_CFB_FILLRECT
 
 config FB_CFB_COPYAREA
 	tristate
-	depends on FB
+	depends on FB_CORE
 	help
 	  Include the cfb_copyarea function for generic software area copying.
 	  This is used by drivers that don't provide their own (accelerated)
@@ -91,7 +103,7 @@ config FB_CFB_COPYAREA
 
 config FB_CFB_IMAGEBLIT
 	tristate
-	depends on FB
+	depends on FB_CORE
 	help
 	  Include the cfb_imageblit function for generic software image
 	  blitting. This is used by drivers that don't provide their own
@@ -99,7 +111,7 @@ config FB_CFB_IMAGEBLIT
 
 config FB_CFB_REV_PIXELS_IN_BYTE
 	bool
-	depends on FB
+	depends on FB_CORE
 	help
 	  Allow generic frame-buffer functions to work on displays with 1, 2
 	  and 4 bits per pixel depths which has opposite order of pixels in
@@ -107,7 +119,7 @@ config FB_CFB_REV_PIXELS_IN_BYTE
 
 config FB_SYS_FILLRECT
 	tristate
-	depends on FB
+	depends on FB_CORE
 	help
 	  Include the sys_fillrect function for generic software rectangle
 	  filling. This is used by drivers that don't provide their own
@@ -115,7 +127,7 @@ config FB_SYS_FILLRECT
 
 config FB_SYS_COPYAREA
 	tristate
-	depends on FB
+	depends on FB_CORE
 	help
 	  Include the sys_copyarea function for generic software area copying.
 	  This is used by drivers that don't provide their own (accelerated)
@@ -123,7 +135,7 @@ config FB_SYS_COPYAREA
 
 config FB_SYS_IMAGEBLIT
 	tristate
-	depends on FB
+	depends on FB_CORE
 	help
 	  Include the sys_imageblit function for generic software image
 	  blitting. This is used by drivers that don't provide their own
@@ -162,22 +174,22 @@ endchoice
 
 config FB_SYS_FOPS
 	tristate
-	depends on FB
+	depends on FB_CORE
 
 config FB_DEFERRED_IO
 	bool
-	depends on FB
+	depends on FB_CORE
 
 config FB_IO_HELPERS
 	bool
-	depends on FB
+	depends on FB_CORE
 	select FB_CFB_COPYAREA
 	select FB_CFB_FILLRECT
 	select FB_CFB_IMAGEBLIT
 
 config FB_SYS_HELPERS
 	bool
-	depends on FB
+	depends on FB_CORE
 	select FB_SYS_COPYAREA
 	select FB_SYS_FILLRECT
 	select FB_SYS_FOPS
@@ -185,34 +197,34 @@ config FB_SYS_HELPERS
 
 config FB_SYS_HELPERS_DEFERRED
 	bool
-	depends on FB
+	depends on FB_CORE
 	select FB_DEFERRED_IO
 	select FB_SYS_HELPERS
 
 config FB_HECUBA
 	tristate
-	depends on FB
+	depends on FB_CORE
 	depends on FB_DEFERRED_IO
 
 config FB_SVGALIB
 	tristate
-	depends on FB
+	depends on FB_CORE
 	help
 	  Common utility functions useful to fbdev drivers of VGA-based
 	  cards.
 
 config FB_MACMODES
 	tristate
-	depends on FB
+	depends on FB_CORE
 
 config FB_BACKLIGHT
 	tristate
-	depends on FB
+	depends on FB_CORE
 	select BACKLIGHT_CLASS_DEVICE
 
 config FB_MODE_HELPERS
 	bool "Enable Video Mode Handling Helpers"
-	depends on FB
+	depends on FB_CORE
 	help
 	  This enables functions for handling video modes using the
 	  Generalized Timing Formula and the EDID parser. A few drivers rely
@@ -222,7 +234,7 @@ config FB_MODE_HELPERS
 
 config FB_TILEBLITTING
 	bool "Enable Tile Blitting Support"
-	depends on FB
+	depends on FB_CORE
 	help
 	  This enables tile blitting.  Tile blitting is a drawing technique
 	  where the screen is divided into rectangular sections (tiles), whereas
diff --git a/drivers/video/fbdev/core/Makefile b/drivers/video/fbdev/core/Makefile
index 9150bafd9e89..88ef39dad03b 100644
--- a/drivers/video/fbdev/core/Makefile
+++ b/drivers/video/fbdev/core/Makefile
@@ -1,22 +1,22 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_FB_NOTIFY)           += fb_notify.o
-obj-$(CONFIG_FB)                  += fb.o
-fb-y                              := fb_backlight.o \
+obj-$(CONFIG_FB_CORE)             += fb_core.o
+fb_core-y                         := fb_backlight.o \
                                      fb_info.o \
                                      fbmem.o fbmon.o fbcmap.o \
                                      modedb.o fbcvt.o fb_cmdline.o fb_io_fops.o
-fb-$(CONFIG_FB_DEFERRED_IO)       += fb_defio.o
-fb-$(CONFIG_FB_DEVICE)            += fb_chrdev.o \
+fb_core-$(CONFIG_FB_DEFERRED_IO)  += fb_defio.o
+fb_core-$(CONFIG_FB_DEVICE)       += fb_chrdev.o \
                                      fb_procfs.o \
                                      fbsysfs.o
 
 ifeq ($(CONFIG_FRAMEBUFFER_CONSOLE),y)
-fb-y				  += fbcon.o bitblit.o softcursor.o
+fb_core-y			  += fbcon.o bitblit.o softcursor.o
 ifeq ($(CONFIG_FB_TILEBLITTING),y)
-fb-y				  += tileblit.o
+fb_core-y			  += tileblit.o
 endif
 ifeq ($(CONFIG_FRAMEBUFFER_CONSOLE_ROTATION),y)
-fb-y				  += fbcon_rotate.o fbcon_cw.o fbcon_ud.o \
+fb_core-y			  += fbcon_rotate.o fbcon_cw.o fbcon_ud.o \
 				     fbcon_ccw.o
 endif
 endif
-- 
2.41.0

Re: [PATCH 1/2] fbdev: Split frame buffer support in FB and FB_CORE symbols

[Arnd Bergmann]

On Fri, Jun 30, 2023, at 00:51, Javier Martinez Canillas wrote:
> Currently the CONFIG_FB option has to be enabled even if no legacy fbdev
> drivers are needed (e.g: only to have support for framebuffer consoles).
>
> The DRM subsystem has a fbdev emulation layer, but depends on CONFIG_FB
> and so it can only be enabled if that dependency is enabled as well.
>
> That means fbdev drivers have to be explicitly disabled if users want to
> enable CONFIG_FB, only to use fbcon and/or the DRM fbdev emulation layer.
>
> This patch introduces a CONFIG_FB_CORE option that could be enabled just
> to have the core support needed for CONFIG_DRM_FBDEV_EMULATION, allowing
> CONFIG_FB to be disabled (and automatically disabling all fbdev drivers).
>
> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
> ---

This looks really nice!

I tried to do something like this a few years ago, but failed as
I did too much at once by attempting to cut out msot of the fb core
support that is not actually used by DRM at the same time.

Doing just the Kconfig bits as you do here is probably better
anyway, cutting out unneeded bits into separate modules or #ifdef
sections can come later.

> @@ -59,7 +71,7 @@ config FIRMWARE_EDID
> 
>  config FB_DEVICE
>  	bool "Provide legacy /dev/fb* device"
> -	depends on FB
> +	depends on FB_CORE
>  	default y
>  	help
>  	  Say Y here if you want the legacy /dev/fb* device file and

I don't see this symbol in linux-next yet, what tree are you using
as a base?

> @@ -69,13 +81,13 @@ config FB_DEVICE
> 
>  config FB_DDC
>  	tristate
> -	depends on FB
> +	depends on FB_CORE
>  	select I2C_ALGOBIT
>  	select I2C

This seems to only be used by actual fbdev drivers, so maybe
don't change the dependency here.

> @@ -162,22 +174,22 @@ endchoice
> 
>  config FB_SYS_FOPS
>  	tristate
> -	depends on FB
> +	depends on FB_CORE

Same for this one

>  config FB_HECUBA
>  	tristate
> -	depends on FB
> +	depends on FB_CORE
>  	depends on FB_DEFERRED_IO
> 
>  config FB_SVGALIB
>  	tristate
> -	depends on FB
> +	depends on FB_CORE
>  	help
>  	  Common utility functions useful to fbdev drivers of VGA-based
>  	  cards.
>  config FB_MACMODES
>  	tristate
> -	depends on FB
> +	depends on FB_CORE
> 

These three seem to actually be part of fbdev drivers rather
than the core, and it may be best to move them into
drviers/video/fbdev/ as standalone modules. That would be a
separate patch of course.
 
>  config FB_BACKLIGHT
>  	tristate
> -	depends on FB
> +	depends on FB_CORE
>  	select BACKLIGHT_CLASS_DEVICE

Separating this one from FB_CORE would help avoid circular dependencies,
this one keeps causing issues.

> @@ -1,22 +1,22 @@
>  # SPDX-License-Identifier: GPL-2.0
>  obj-$(CONFIG_FB_NOTIFY)           += fb_notify.o
> -obj-$(CONFIG_FB)                  += fb.o
> -fb-y                              := fb_backlight.o \
> +obj-$(CONFIG_FB_CORE)             += fb_core.o
> +fb_core-y                         := fb_backlight.o \
>                                       fb_info.o \
>                                       fbmem.o fbmon.o fbcmap.o \
>                                       modedb.o fbcvt.o fb_cmdline.o 

I would not bother renaming the module itself here, that
might cause problems if anything relies on loading the
module by name or a named module parameter.

      Arnd

Re: [PATCH 1/2] fbdev: Split frame buffer support in FB and FB_CORE symbols

[Javier Martinez Canillas]

"Arnd Bergmann" <arnd@arndb.de> writes:

Hello Arnd,

Thanks for your review!

> On Fri, Jun 30, 2023, at 00:51, Javier Martinez Canillas wrote:
>> Currently the CONFIG_FB option has to be enabled even if no legacy fbdev
>> drivers are needed (e.g: only to have support for framebuffer consoles).
>>
>> The DRM subsystem has a fbdev emulation layer, but depends on CONFIG_FB
>> and so it can only be enabled if that dependency is enabled as well.
>>
>> That means fbdev drivers have to be explicitly disabled if users want to
>> enable CONFIG_FB, only to use fbcon and/or the DRM fbdev emulation layer.
>>
>> This patch introduces a CONFIG_FB_CORE option that could be enabled just
>> to have the core support needed for CONFIG_DRM_FBDEV_EMULATION, allowing
>> CONFIG_FB to be disabled (and automatically disabling all fbdev drivers).
>>
>> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
>> ---
>
> This looks really nice!
>
> I tried to do something like this a few years ago, but failed as

Yes, I also tried to do this before some time ago [0]:

[0]: https://lore.kernel.org/lkml/20210827100027.1577561-1-javierm@redhat.com/t/#mc8bb6cda8c2d795673618049b6c834b34bf86162

and at the time required some code refactoring but now thanks to all the
cleanups that Thomas has been doing over, I could just do it with Kconfig.

> I did too much at once by attempting to cut out msot of the fb core
> support that is not actually used by DRM at the same time.
>
> Doing just the Kconfig bits as you do here is probably better
> anyway, cutting out unneeded bits into separate modules or #ifdef
> sections can come later.
>

Exactly, that was my thought too. Glad that you agree with the approach.

>> @@ -59,7 +71,7 @@ config FIRMWARE_EDID
>> 
>>  config FB_DEVICE
>>  	bool "Provide legacy /dev/fb* device"
>> -	depends on FB
>> +	depends on FB_CORE
>>  	default y
>>  	help
>>  	  Say Y here if you want the legacy /dev/fb* device file and
>
> I don't see this symbol in linux-next yet, what tree are you using
> as a base?
>

It's now in the drm-misc/drm-misc-next branch [1]. It's not in -next yet
because it just landed a few days ago [2].

[1]: https://cgit.freedesktop.org/drm/drm-misc/log/?h=drm-misc-next
[2]: https://cgit.freedesktop.org/drm/drm-misc/commit/?id=701d2054fa3

In fact, that's the reason why I rebased my previous attempt [0].

>> @@ -69,13 +81,13 @@ config FB_DEVICE
>> 
>>  config FB_DDC
>>  	tristate
>> -	depends on FB
>> +	depends on FB_CORE
>>  	select I2C_ALGOBIT
>>  	select I2C
>
> This seems to only be used by actual fbdev drivers, so maybe
> don't change the dependency here.
>

Indeed.

>> @@ -162,22 +174,22 @@ endchoice
>> 
>>  config FB_SYS_FOPS
>>  	tristate
>> -	depends on FB
>> +	depends on FB_CORE
>
> Same for this one
>

Ok.

>>  config FB_HECUBA
>>  	tristate
>> -	depends on FB
>> +	depends on FB_CORE
>>  	depends on FB_DEFERRED_IO
>> 
>>  config FB_SVGALIB
>>  	tristate
>> -	depends on FB
>> +	depends on FB_CORE
>>  	help
>>  	  Common utility functions useful to fbdev drivers of VGA-based
>>  	  cards.
>>  config FB_MACMODES
>>  	tristate
>> -	depends on FB
>> +	depends on FB_CORE
>> 
>
> These three seem to actually be part of fbdev drivers rather
> than the core, and it may be best to move them into
> drviers/video/fbdev/ as standalone modules. That would be a
> separate patch of course.
>

Agreed. I'll then also don't change the dependency on these ones.

>>  config FB_BACKLIGHT
>>  	tristate
>> -	depends on FB
>> +	depends on FB_CORE
>>  	select BACKLIGHT_CLASS_DEVICE
>
> Separating this one from FB_CORE would help avoid circular dependencies,
> this one keeps causing issues.
>

You mean separating from FB or should I keep the existing depends on FB?

It seems this is only used by fbdev drivers so probably the latter?

>> @@ -1,22 +1,22 @@
>>  # SPDX-License-Identifier: GPL-2.0
>>  obj-$(CONFIG_FB_NOTIFY)           += fb_notify.o
>> -obj-$(CONFIG_FB)                  += fb.o
>> -fb-y                              := fb_backlight.o \
>> +obj-$(CONFIG_FB_CORE)             += fb_core.o
>> +fb_core-y                         := fb_backlight.o \
>>                                       fb_info.o \
>>                                       fbmem.o fbmon.o fbcmap.o \
>>                                       modedb.o fbcvt.o fb_cmdline.o 
>
> I would not bother renaming the module itself here, that
> might cause problems if anything relies on loading the
> module by name or a named module parameter.
>

I was actually not sure about this, but then thought that someone could
had complained that the Kconfig symbol and module name wouldn't match :)

I'll just keep the existing module name then and drop the rename.

>       Arnd
>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat

Re: [PATCH 1/2] fbdev: Split frame buffer support in FB and FB_CORE symbols

[Arnd Bergmann]

On Fri, Jun 30, 2023, at 12:51, Javier Martinez Canillas wrote:
> "Arnd Bergmann" <arnd@arndb.de> writes:
>
>>> @@ -59,7 +71,7 @@ config FIRMWARE_EDID
>>> 
>>>  config FB_DEVICE
>>>  	bool "Provide legacy /dev/fb* device"
>>> -	depends on FB
>>> +	depends on FB_CORE
>>>  	default y
>>>  	help
>>>  	  Say Y here if you want the legacy /dev/fb* device file and
>>
>> I don't see this symbol in linux-next yet, what tree are you using
>> as a base?
>>
>
> It's now in the drm-misc/drm-misc-next branch [1]. It's not in -next yet
> because it just landed a few days ago [2].
>
> [1]: https://cgit.freedesktop.org/drm/drm-misc/log/?h=drm-misc-next
> [2]: https://cgit.freedesktop.org/drm/drm-misc/commit/?id=701d2054fa3
>
> In fact, that's the reason why I rebased my previous attempt [0].

Ok.

I wonder if it would make sense to also make FB_DEVICE depend on FB
instead of FB_CORE then. I don't think there is any actual dependency
between the two, but as I understand we want modern distros to use
neither FB nor FB_DEVICE, so tying them together with a dependency
may be desirable anyway.


>>>  config FB_BACKLIGHT
>>>  	tristate
>>> -	depends on FB
>>> +	depends on FB_CORE
>>>  	select BACKLIGHT_CLASS_DEVICE
>>
>> Separating this one from FB_CORE would help avoid circular dependencies,
>> this one keeps causing issues.
>>
>
> You mean separating from FB or should I keep the existing depends on FB?
>
> It seems this is only used by fbdev drivers so probably the latter?

Right, I meant keeping the dependency on FB. Ideally we'd
turn this all into a set of 'depends on' instead of 'select',
but that is a completely separate topic.

    Arnd

Re: [PATCH 1/2] fbdev: Split frame buffer support in FB and FB_CORE symbols

[Javier Martinez Canillas]

"Arnd Bergmann" <arnd@arndb.de> writes:

> On Fri, Jun 30, 2023, at 12:51, Javier Martinez Canillas wrote:
>> "Arnd Bergmann" <arnd@arndb.de> writes:
>>
>>>> @@ -59,7 +71,7 @@ config FIRMWARE_EDID
>>>> 
>>>>  config FB_DEVICE
>>>>  	bool "Provide legacy /dev/fb* device"
>>>> -	depends on FB
>>>> +	depends on FB_CORE
>>>>  	default y
>>>>  	help
>>>>  	  Say Y here if you want the legacy /dev/fb* device file and
>>>
>>> I don't see this symbol in linux-next yet, what tree are you using
>>> as a base?
>>>
>>
>> It's now in the drm-misc/drm-misc-next branch [1]. It's not in -next yet
>> because it just landed a few days ago [2].
>>
>> [1]: https://cgit.freedesktop.org/drm/drm-misc/log/?h=drm-misc-next
>> [2]: https://cgit.freedesktop.org/drm/drm-misc/commit/?id=701d2054fa3
>>
>> In fact, that's the reason why I rebased my previous attempt [0].
>
> Ok.
>
> I wonder if it would make sense to also make FB_DEVICE depend on FB
> instead of FB_CORE then. I don't think there is any actual dependency

No, because that wouldn't allow to have /dev/fb* devices when using the
DRM fbdev emulation layer. It could be the case that users have an old
fbdev user-space but the platform only has a DRM driver, in that case we
want to disable all native fbdev drivers (CONFIG_FB not set) but still
have FB_CORE, FB_DEVICE and DRM_FBDEV_EMULATION options enabled.

> between the two, but as I understand we want modern distros to use
> neither FB nor FB_DEVICE, so tying them together with a dependency
> may be desirable anyway.
>

As said, modern distros would want to disable both FB and FB_DEVICE, but
we want to allow for these two options to be {en,dis}abled independently.

>
>>>>  config FB_BACKLIGHT
>>>>  	tristate
>>>> -	depends on FB
>>>> +	depends on FB_CORE
>>>>  	select BACKLIGHT_CLASS_DEVICE
>>>
>>> Separating this one from FB_CORE would help avoid circular dependencies,
>>> this one keeps causing issues.
>>>
>>
>> You mean separating from FB or should I keep the existing depends on FB?
>>
>> It seems this is only used by fbdev drivers so probably the latter?
>
> Right, I meant keeping the dependency on FB. Ideally we'd
> turn this all into a set of 'depends on' instead of 'select',
> but that is a completely separate topic.
>

Ok.

>     Arnd
>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat

Re: [PATCH 0/2] Allow disabling all native fbdev drivers and only keeping DRM emulation

[Thomas Zimmermann]

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Hi Javier

Am 30.06.23 um 00:51 schrieb Javier Martinez Canillas:
> This patch series splits the fbdev core support in two different Kconfig
> symbols: FB and FB_CORE. The motivation for this is to allow CONFIG_FB to
> be disabled, while still having the the core fbdev support needed for the
> CONFIG_DRM_FBDEV_EMULATION to be enabled. The motivation is automatically
> disabling all fbdev drivers instead of having to be disabled individually.
> 
> The reason for doing this is that now with simpledrm, there's no need for
> the legacy fbdev (e.g: efifb or vesafb) drivers anymore and many distros
> now disable them. But it would simplify the config a lot fo have a single
> Kconfig symbol to disable all fbdev drivers.

I still don't get the point of this change. We've disabled the fbdev 
drivers once. And they are off now and remain off.

The patchset now introduces FB_CORE, which just adds more options. But 
you're not reducing the code or compile time or any thing similar.

I'd like to suggest a change to these patches: rather then making FB and 
DRM_FBDEV_EMULATION depend on FB_CORE, make them select FB_CORE. That 
will allow the DRM subsystem to enable framebuffer emulation 
independently from framebuffer devices. If either has been set, the 
fbdev core will be selected.

Best regards
Thomas

> 
> I've build tested with possible combinations of CONFIG_FB, CONFIG_FB_CORE,
> CONFIG_DRM_FBDEV_EMULATION and CONFIG_FB_DEVICE symbols set to 'y' or 'n'.
> 
> Patch 1/2 makes the CONFIG_FB split that is mentioned above and patch 2/2
> makes DRM fbdev emulation depend on the new FB_CORE symbol instead of FB.
> 
> 
> Javier Martinez Canillas (2):
>    fbdev: Split frame buffer support in FB and FB_CORE symbols
>    drm: Make fbdev emulation depend on FB_CORE instead of FB
> 
>   arch/x86/Makefile                 |  2 +-
>   arch/x86/video/Makefile           |  2 +-
>   drivers/gpu/drm/Kconfig           |  2 +-
>   drivers/video/console/Kconfig     |  2 +-
>   drivers/video/fbdev/Kconfig       | 62 ++++++++++++++++++-------------
>   drivers/video/fbdev/core/Makefile | 14 +++----
>   6 files changed, 48 insertions(+), 36 deletions(-)
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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Re: [PATCH 0/2] Allow disabling all native fbdev drivers and only keeping DRM emulation

[Javier Martinez Canillas]

Thomas Zimmermann <tzimmermann@suse.de> writes:

Hello Thomas,

Thanks a lot for your review.

> Hi Javier
>
> Am 30.06.23 um 00:51 schrieb Javier Martinez Canillas:
>> This patch series splits the fbdev core support in two different Kconfig
>> symbols: FB and FB_CORE. The motivation for this is to allow CONFIG_FB to
>> be disabled, while still having the the core fbdev support needed for the
>> CONFIG_DRM_FBDEV_EMULATION to be enabled. The motivation is automatically
>> disabling all fbdev drivers instead of having to be disabled individually.
>> 
>> The reason for doing this is that now with simpledrm, there's no need for
>> the legacy fbdev (e.g: efifb or vesafb) drivers anymore and many distros
>> now disable them. But it would simplify the config a lot fo have a single
>> Kconfig symbol to disable all fbdev drivers.
>
> I still don't get the point of this change. We've disabled the fbdev 
> drivers once. And they are off now and remain off.
>

Yes, but doing that means you have a bunch of these in your kernel config:

#
# Frame buffer hardware drivers
#
# CONFIG_FB_CIRRUS is not set
# CONFIG_FB_PM2 is not set
# CONFIG_FB_ARMCLCD is not set
...

I don't know how the kernel configuration management for the OpenSUSE
kernel package works, but at least in Fedora this translates to needing to
have a lot of explicit disable configurations in the form of:

$ cat redhat/configs/common/generic/CONFIG_FB_CIRRUS 
# CONFIG_FB_CIRRUS is not set

$ ls redhat/configs/common/generic/CONFIG_FB_* | wc -l
61

I want to get rid of all those and the goal of this series is to reduce
that configuration to only:

$ cat redhat/configs/common/generic/CONFIG_FB
# CONFIG_FB is not set

$ cat redhat/configs/common/generic/CONFIG_FB_CORE
CONFIG_FB_CORE=y

> The patchset now introduces FB_CORE, which just adds more options. But 
> you're not reducing the code or compile time or any thing similar.
>

No need for any redhat/configs/common/generic/CONFIG_FB_* because those
don't need to be explicitly disabled anymore since CONFIG_FB isn't set.

And the "Frame buffer hardware drivers" section in the .config goes away.

So it is a configuration simplification even when you can achieve the same
with the existing Kconfig symbols.

> I'd like to suggest a change to these patches: rather then making FB and 
> DRM_FBDEV_EMULATION depend on FB_CORE, make them select FB_CORE. That 
> will allow the DRM subsystem to enable framebuffer emulation 
> independently from framebuffer devices. If either has been set, the 
> fbdev core will be selected.
>

Yes, I guess that making it a non user-visible option makes sense. I'm
just wary of using select because I've bitten in the past by circular
dependencies when other symbol depends on it.

But I'm OK with that change and will do in v2.

> Best regards
> Thomas
>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat

Re: [PATCH 0/2] Allow disabling all native fbdev drivers and only keeping DRM emulation

[Thomas Zimmermann]

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Hi

Am 30.06.23 um 14:33 schrieb Javier Martinez Canillas:
> Thomas Zimmermann <tzimmermann@suse.de> writes:
> 
> Hello Thomas,
> 
> Thanks a lot for your review.
> 
>> Hi Javier
>>
>> Am 30.06.23 um 00:51 schrieb Javier Martinez Canillas:
>>> This patch series splits the fbdev core support in two different Kconfig
>>> symbols: FB and FB_CORE. The motivation for this is to allow CONFIG_FB to
>>> be disabled, while still having the the core fbdev support needed for the
>>> CONFIG_DRM_FBDEV_EMULATION to be enabled. The motivation is automatically
>>> disabling all fbdev drivers instead of having to be disabled individually.
>>>
>>> The reason for doing this is that now with simpledrm, there's no need for
>>> the legacy fbdev (e.g: efifb or vesafb) drivers anymore and many distros
>>> now disable them. But it would simplify the config a lot fo have a single
>>> Kconfig symbol to disable all fbdev drivers.
>>
>> I still don't get the point of this change. We've disabled the fbdev
>> drivers once. And they are off now and remain off.
>>
> 
> Yes, but doing that means you have a bunch of these in your kernel config:
> 
> #
> # Frame buffer hardware drivers
> #
> # CONFIG_FB_CIRRUS is not set
> # CONFIG_FB_PM2 is not set
> # CONFIG_FB_ARMCLCD is not set
> ...
> 
> I don't know how the kernel configuration management for the OpenSUSE
> kernel package works, but at least in Fedora this translates to needing to
> have a lot of explicit disable configurations in the form of:
> 
> $ cat redhat/configs/common/generic/CONFIG_FB_CIRRUS
> # CONFIG_FB_CIRRUS is not set
> 
> $ ls redhat/configs/common/generic/CONFIG_FB_* | wc -l
> 61
> 
> I want to get rid of all those and the goal of this series is to reduce
> that configuration to only:
> 
> $ cat redhat/configs/common/generic/CONFIG_FB
> # CONFIG_FB is not set
> 
> $ cat redhat/configs/common/generic/CONFIG_FB_CORE
> CONFIG_FB_CORE=y

We have these 'is not set' lines on our kernel configs, but I don't 
think they bother anyone too much.

Well, thanks for explaining. At least I now see why you want to do this 
change.

> 
>> The patchset now introduces FB_CORE, which just adds more options. But
>> you're not reducing the code or compile time or any thing similar.
>>
> 
> No need for any redhat/configs/common/generic/CONFIG_FB_* because those
> don't need to be explicitly disabled anymore since CONFIG_FB isn't set.
> 
> And the "Frame buffer hardware drivers" section in the .config goes away.
> 
> So it is a configuration simplification even when you can achieve the same
> with the existing Kconfig symbols.
> 
>> I'd like to suggest a change to these patches: rather then making FB and
>> DRM_FBDEV_EMULATION depend on FB_CORE, make them select FB_CORE. That
>> will allow the DRM subsystem to enable framebuffer emulation
>> independently from framebuffer devices. If either has been set, the
>> fbdev core will be selected.
>>
> 
> Yes, I guess that making it a non user-visible option makes sense. I'm
> just wary of using select because I've bitten in the past by circular
> dependencies when other symbol depends on it.
> 
> But I'm OK with that change and will do in v2.

Great, thanks.

Best regards
Thomas

> 
>> Best regards
>> Thomas
>>
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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Re: [PATCH 0/2] Allow disabling all native fbdev drivers and only keeping DRM emulation

[Arnd Bergmann]

On Fri, Jun 30, 2023, at 13:19, Thomas Zimmermann wrote:
> Am 30.06.23 um 00:51 schrieb Javier Martinez Canillas:
>> This patch series splits the fbdev core support in two different Kconfig
>> symbols: FB and FB_CORE. The motivation for this is to allow CONFIG_FB to
>> be disabled, while still having the the core fbdev support needed for the
>> CONFIG_DRM_FBDEV_EMULATION to be enabled. The motivation is automatically
>> disabling all fbdev drivers instead of having to be disabled individually.
>> 
>> The reason for doing this is that now with simpledrm, there's no need for
>> the legacy fbdev (e.g: efifb or vesafb) drivers anymore and many distros
>> now disable them. But it would simplify the config a lot fo have a single
>> Kconfig symbol to disable all fbdev drivers.
>
> I still don't get the point of this change. We've disabled the fbdev 
> drivers once. And they are off now and remain off.
>
> The patchset now introduces FB_CORE, which just adds more options. But 
> you're not reducing the code or compile time or any thing similar.
>
> I'd like to suggest a change to these patches: rather then making FB and 
> DRM_FBDEV_EMULATION depend on FB_CORE, make them select FB_CORE. That 
> will allow the DRM subsystem to enable framebuffer emulation 
> independently from framebuffer devices. If either has been set, the 
> fbdev core will be selected.

I agree with making FB_CORE a hidden option that gets selected by FB
and DRM_FBDEV_EMULATION, without that we will get a whole lot of new
build regressions for people that don't update their defconfigs,
like we had when we removed the 'select FB' in DRM.

Aside from that, the changes look very useful to me.

      Arnd

Re: [PATCH 0/2] Allow disabling all native fbdev drivers and only keeping DRM emulation

[Andy Shevchenko]

On Fri, Jun 30, 2023 at 12:51:02AM +0200, Javier Martinez Canillas wrote:
> This patch series splits the fbdev core support in two different Kconfig
> symbols: FB and FB_CORE. The motivation for this is to allow CONFIG_FB to
> be disabled, while still having the the core fbdev support needed for the
> CONFIG_DRM_FBDEV_EMULATION to be enabled. The motivation is automatically
> disabling all fbdev drivers instead of having to be disabled individually.
> 
> The reason for doing this is that now with simpledrm, there's no need for
> the legacy fbdev (e.g: efifb or vesafb) drivers anymore and many distros

How does simpledrm works with earlycon=efi?

> now disable them. But it would simplify the config a lot fo have a single
> Kconfig symbol to disable all fbdev drivers.
> 
> I've build tested with possible combinations of CONFIG_FB, CONFIG_FB_CORE,
> CONFIG_DRM_FBDEV_EMULATION and CONFIG_FB_DEVICE symbols set to 'y' or 'n'.
> 
> Patch 1/2 makes the CONFIG_FB split that is mentioned above and patch 2/2
> makes DRM fbdev emulation depend on the new FB_CORE symbol instead of FB.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH 0/2] Allow disabling all native fbdev drivers and only keeping DRM emulation

[Javier Martinez Canillas]

Andy Shevchenko <andriy.shevchenko@linux.intel.com> writes:

Hello Andy,

> On Fri, Jun 30, 2023 at 12:51:02AM +0200, Javier Martinez Canillas wrote:
>> This patch series splits the fbdev core support in two different Kconfig
>> symbols: FB and FB_CORE. The motivation for this is to allow CONFIG_FB to
>> be disabled, while still having the the core fbdev support needed for the
>> CONFIG_DRM_FBDEV_EMULATION to be enabled. The motivation is automatically
>> disabling all fbdev drivers instead of having to be disabled individually.
>> 
>> The reason for doing this is that now with simpledrm, there's no need for
>> the legacy fbdev (e.g: efifb or vesafb) drivers anymore and many distros
>
> How does simpledrm works with earlycon=efi?
>

simpledrm isn't for earlycon. For that you use a different driver (i.e:
drivers/firmware/efi/earlycon.c). I'm just talking about fbdev drivers
here that could be replaced by simpledrm.

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat

Re: [PATCH 0/2] Allow disabling all native fbdev drivers and only keeping DRM emulation

[Andy Shevchenko]

On Fri, Jun 30, 2023 at 07:38:01PM +0200, Javier Martinez Canillas wrote:
> Andy Shevchenko <andriy.shevchenko@linux.intel.com> writes:
> > On Fri, Jun 30, 2023 at 12:51:02AM +0200, Javier Martinez Canillas wrote:
> >> This patch series splits the fbdev core support in two different Kconfig
> >> symbols: FB and FB_CORE. The motivation for this is to allow CONFIG_FB to
> >> be disabled, while still having the the core fbdev support needed for the
> >> CONFIG_DRM_FBDEV_EMULATION to be enabled. The motivation is automatically
> >> disabling all fbdev drivers instead of having to be disabled individually.
> >> 
> >> The reason for doing this is that now with simpledrm, there's no need for
> >> the legacy fbdev (e.g: efifb or vesafb) drivers anymore and many distros
> >
> > How does simpledrm works with earlycon=efi?
> >
> 
> simpledrm isn't for earlycon. For that you use a different driver (i.e:
> drivers/firmware/efi/earlycon.c). I'm just talking about fbdev drivers
> here that could be replaced by simpledrm.

So, efifb can't be replaced. Please, fix your cover letter to reduce false
impression of the scope of usage of the simpledrm.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH 0/2] Allow disabling all native fbdev drivers and only keeping DRM emulation

[Andy Shevchenko]

On Fri, Jun 30, 2023 at 08:42:21PM +0300, Andy Shevchenko wrote:
> On Fri, Jun 30, 2023 at 07:38:01PM +0200, Javier Martinez Canillas wrote:
> > Andy Shevchenko <andriy.shevchenko@linux.intel.com> writes:
> > > On Fri, Jun 30, 2023 at 12:51:02AM +0200, Javier Martinez Canillas wrote:

...

> > >> The reason for doing this is that now with simpledrm, there's no need for
> > >> the legacy fbdev (e.g: efifb or vesafb) drivers anymore and many distros
> > >
> > > How does simpledrm works with earlycon=efi?
> > >
> > 
> > simpledrm isn't for earlycon. For that you use a different driver (i.e:
> > drivers/firmware/efi/earlycon.c). I'm just talking about fbdev drivers
> > here that could be replaced by simpledrm.
> 
> So, efifb can't be replaced. Please, fix your cover letter to reduce false
> impression of the scope of usage of the simpledrm.

Or tell how it can be used for earlycon on EFI platforms (if it can be).

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH 0/2] Allow disabling all native fbdev drivers and only keeping DRM emulation

[Javier Martinez Canillas]

Andy Shevchenko <andriy.shevchenko@linux.intel.com> writes:

> On Fri, Jun 30, 2023 at 07:38:01PM +0200, Javier Martinez Canillas wrote:
>> Andy Shevchenko <andriy.shevchenko@linux.intel.com> writes:
>> > On Fri, Jun 30, 2023 at 12:51:02AM +0200, Javier Martinez Canillas wrote:
>> >> This patch series splits the fbdev core support in two different Kconfig
>> >> symbols: FB and FB_CORE. The motivation for this is to allow CONFIG_FB to
>> >> be disabled, while still having the the core fbdev support needed for the
>> >> CONFIG_DRM_FBDEV_EMULATION to be enabled. The motivation is automatically
>> >> disabling all fbdev drivers instead of having to be disabled individually.
>> >> 
>> >> The reason for doing this is that now with simpledrm, there's no need for
>> >> the legacy fbdev (e.g: efifb or vesafb) drivers anymore and many distros
>> >
>> > How does simpledrm works with earlycon=efi?
>> >
>> 
>> simpledrm isn't for earlycon. For that you use a different driver (i.e:
>> drivers/firmware/efi/earlycon.c). I'm just talking about fbdev drivers
>> here that could be replaced by simpledrm.
>
> So, efifb can't be replaced. Please, fix your cover letter to reduce false
> impression of the scope of usage of the simpledrm.
>

Nothing to fixup.

You are conflating the efifb fbdev driver (drivers/video/fbdev/efifb.c)
with the efifb earlycon driver (drivers/firmware/efi/earlycon.c). I'm
talking about the former (which can be replaced by simpledrm) while you
are talking about the latter.

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat

Re: [PATCH 0/2] Allow disabling all native fbdev drivers and only keeping DRM emulation

[Andy Shevchenko]

On Fri, Jun 30, 2023 at 10:29:20PM +0200, Javier Martinez Canillas wrote:
> Andy Shevchenko <andriy.shevchenko@linux.intel.com> writes:
> > On Fri, Jun 30, 2023 at 07:38:01PM +0200, Javier Martinez Canillas wrote:
> >> Andy Shevchenko <andriy.shevchenko@linux.intel.com> writes:
> >> > On Fri, Jun 30, 2023 at 12:51:02AM +0200, Javier Martinez Canillas wrote:
> >> >> This patch series splits the fbdev core support in two different Kconfig
> >> >> symbols: FB and FB_CORE. The motivation for this is to allow CONFIG_FB to
> >> >> be disabled, while still having the the core fbdev support needed for the
> >> >> CONFIG_DRM_FBDEV_EMULATION to be enabled. The motivation is automatically
> >> >> disabling all fbdev drivers instead of having to be disabled individually.
> >> >> 
> >> >> The reason for doing this is that now with simpledrm, there's no need for
> >> >> the legacy fbdev (e.g: efifb or vesafb) drivers anymore and many distros
> >> >
> >> > How does simpledrm works with earlycon=efi?
> >> >
> >> 
> >> simpledrm isn't for earlycon. For that you use a different driver (i.e:
> >> drivers/firmware/efi/earlycon.c). I'm just talking about fbdev drivers
> >> here that could be replaced by simpledrm.
> >
> > So, efifb can't be replaced. Please, fix your cover letter to reduce false
> > impression of the scope of usage of the simpledrm.
> >
> 
> Nothing to fixup.
> 
> You are conflating the efifb fbdev driver (drivers/video/fbdev/efifb.c)
> with the efifb earlycon driver (drivers/firmware/efi/earlycon.c). I'm
> talking about the former (which can be replaced by simpledrm) while you
> are talking about the latter.

Ah, this makes sense!

I remember now that it was (still is?) an attempt to move from efifb to
simpledrm, but have no idea what the status of that series is.

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH 0/2] Allow disabling all native fbdev drivers and only keeping DRM emulation

[Javier Martinez Canillas]

Andy Shevchenko <andriy.shevchenko@linux.intel.com> writes:

> On Fri, Jun 30, 2023 at 10:29:20PM +0200, Javier Martinez Canillas wrote:
>> Andy Shevchenko <andriy.shevchenko@linux.intel.com> writes:
>> > On Fri, Jun 30, 2023 at 07:38:01PM +0200, Javier Martinez Canillas wrote:
>> >> Andy Shevchenko <andriy.shevchenko@linux.intel.com> writes:
>> >> > On Fri, Jun 30, 2023 at 12:51:02AM +0200, Javier Martinez Canillas wrote:
>> >> >> This patch series splits the fbdev core support in two different Kconfig
>> >> >> symbols: FB and FB_CORE. The motivation for this is to allow CONFIG_FB to
>> >> >> be disabled, while still having the the core fbdev support needed for the
>> >> >> CONFIG_DRM_FBDEV_EMULATION to be enabled. The motivation is automatically
>> >> >> disabling all fbdev drivers instead of having to be disabled individually.
>> >> >> 
>> >> >> The reason for doing this is that now with simpledrm, there's no need for
>> >> >> the legacy fbdev (e.g: efifb or vesafb) drivers anymore and many distros
>> >> >
>> >> > How does simpledrm works with earlycon=efi?
>> >> >
>> >> 
>> >> simpledrm isn't for earlycon. For that you use a different driver (i.e:
>> >> drivers/firmware/efi/earlycon.c). I'm just talking about fbdev drivers
>> >> here that could be replaced by simpledrm.
>> >
>> > So, efifb can't be replaced. Please, fix your cover letter to reduce false
>> > impression of the scope of usage of the simpledrm.
>> >
>> 
>> Nothing to fixup.
>> 
>> You are conflating the efifb fbdev driver (drivers/video/fbdev/efifb.c)
>> with the efifb earlycon driver (drivers/firmware/efi/earlycon.c). I'm
>> talking about the former (which can be replaced by simpledrm) while you
>> are talking about the latter.
>
> Ah, this makes sense!
>
> I remember now that it was (still is?) an attempt to move from efifb to
> simpledrm, but have no idea what the status of that series is.
>

Indeed. And there was were also some patches IIRC to attempt porting the
earlycon efifb to a fbdev or DRM driver, can't remember now.

> -- 
> With Best Regards,
> Andy Shevchenko
>
>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat