[6/8] drm: decouple from CONFIG_FB

Message ID 20200417155553.675905-7-arnd@arndb.de
State New
Headers show
Series
  • drm, fbdev: rework dependencies
Related show

Commit Message

Arnd Bergmann April 17, 2020, 3:55 p.m.
CONFIG_DRM_KMS_FB_HELPER selects CONFIG_FB, which is something it
really should not, to avoid circular dependencies and accidentally
including potentially dangerous user interfaces in the kernel,
so change this into a 'depends on' check.

Two device drivers currently select CONFIG_DRM_KMS_FB_HELPER, but
as far as I can tell, they do not really need to any more, so those
selects can be removed.

This leaves DRM_FBDEV_EMULATION as the only thing that rightfully
selects CONFIG_DRM_KMS_FB_HELPER, and this now has to depend on
CONFIG_FB and its dependencies.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>

---
 drivers/gpu/drm/Kconfig       | 5 +++--
 drivers/gpu/drm/mxsfb/Kconfig | 1 -
 drivers/gpu/drm/zte/Kconfig   | 1 -
 3 files changed, 3 insertions(+), 4 deletions(-)

-- 
2.26.0

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Comments

Sam Ravnborg April 17, 2020, 4:50 p.m. | #1
Hi Arnd.

On Fri, Apr 17, 2020 at 05:55:51PM +0200, Arnd Bergmann wrote:
> CONFIG_DRM_KMS_FB_HELPER selects CONFIG_FB, which is something it

> really should not, to avoid circular dependencies and accidentally

> including potentially dangerous user interfaces in the kernel,

> so change this into a 'depends on' check.

> 

> Two device drivers currently select CONFIG_DRM_KMS_FB_HELPER, but

> as far as I can tell, they do not really need to any more, so those

> selects can be removed.

> 

> This leaves DRM_FBDEV_EMULATION as the only thing that rightfully

> selects CONFIG_DRM_KMS_FB_HELPER, and this now has to depend on

> CONFIG_FB and its dependencies.

> 

> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

> ---

>  drivers/gpu/drm/Kconfig       | 5 +++--

>  drivers/gpu/drm/mxsfb/Kconfig | 1 -

>  drivers/gpu/drm/zte/Kconfig   | 1 -

>  3 files changed, 3 insertions(+), 4 deletions(-)

> 

> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig

> index 43594978958e..7c3109133685 100644

> --- a/drivers/gpu/drm/Kconfig

> +++ b/drivers/gpu/drm/Kconfig

> @@ -80,7 +80,7 @@ config DRM_KMS_HELPER

>  config DRM_KMS_FB_HELPER

>  	bool

>  	depends on DRM_KMS_HELPER

> -	select FB

> +	depends on FB

>  	select FRAMEBUFFER_CONSOLE if !EXPERT

>  	select FRAMEBUFFER_CONSOLE_DETECT_PRIMARY if FRAMEBUFFER_CONSOLE

>  	select FB_SYS_FOPS

> @@ -111,7 +111,8 @@ config DRM_DEBUG_DP_MST_TOPOLOGY_REFS

>  

>  config DRM_FBDEV_EMULATION

>  	bool "Enable legacy fbdev support for your modesetting driver"

> -	depends on DRM

> +	depends on DRM && FB

> +	depends on FB=y || DRM=m

>  	select DRM_KMS_HELPER

>  	select DRM_KMS_FB_HELPER

>  	default y

This statement:

	depends on DRM && FB

tell us that both symbols must be either y or m. Any combination of y
and m will do the trick


Then we have this statement:

	depends on FB=y || DRM=m

It tells us that either FB equals y or DRM equals m.

So we have following table

	FB	DRM	Result
	n	n	n
	n	y	n
	n	m	n
	y	n	n
	y	y	y
	y	m	y
	m	n	n
	m	y	N
	m	m	y

So what this try to say is that we cannot have FB a module while DRM is
built-in (marked N in the above).

Could you explain in the changelog why this combination is not good.
(Or tell me if my analysis was flawed).

With this fixed (assuming I am right):
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>


	Sam

> diff --git a/drivers/gpu/drm/mxsfb/Kconfig b/drivers/gpu/drm/mxsfb/Kconfig

> index 0dca8f27169e..33916b7b2c50 100644

> --- a/drivers/gpu/drm/mxsfb/Kconfig

> +++ b/drivers/gpu/drm/mxsfb/Kconfig

> @@ -10,7 +10,6 @@ config DRM_MXSFB

>  	depends on COMMON_CLK

>  	select DRM_MXS

>  	select DRM_KMS_HELPER

> -	select DRM_KMS_FB_HELPER

>  	select DRM_KMS_CMA_HELPER

>  	select DRM_PANEL

>  	help

> diff --git a/drivers/gpu/drm/zte/Kconfig b/drivers/gpu/drm/zte/Kconfig

> index 90ebaedc11fd..aa8594190b50 100644

> --- a/drivers/gpu/drm/zte/Kconfig

> +++ b/drivers/gpu/drm/zte/Kconfig

> @@ -3,7 +3,6 @@ config DRM_ZTE

>  	tristate "DRM Support for ZTE SoCs"

>  	depends on DRM && ARCH_ZX

>  	select DRM_KMS_CMA_HELPER

> -	select DRM_KMS_FB_HELPER

>  	select DRM_KMS_HELPER

>  	select SND_SOC_HDMI_CODEC if SND_SOC

>  	select VIDEOMODE_HELPERS

> -- 

> 2.26.0

> 

> _______________________________________________

> dri-devel mailing list

> dri-devel@lists.freedesktop.org

> https://lists.freedesktop.org/mailman/listinfo/dri-devel

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Arnd Bergmann April 17, 2020, 8:03 p.m. | #2
On Fri, Apr 17, 2020 at 6:50 PM Sam Ravnborg <sam@ravnborg.org> wrote:

>

> So what this try to say is that we cannot have FB a module while DRM is

> built-in (marked N in the above).


Correct

>

> Could you explain in the changelog why this combination is not good.

> (Or tell me if my analysis was flawed).


I agree in hindsight this was less obvious than I thought ;-)

Added this text to the changelog:

|  When CONFIG_FB is a loadable module, DRM_KMS_FB_HELPER cannot be
| part of the built-in subsystem, so add dependency to ensure this
| can only be enabled if the DRM module can successfully be linked.

and this comment in the Kconfig file:

@@ -112,7 +112,7 @@ config DRM_DEBUG_DP_MST_TOPOLOGY_REFS
 config DRM_FBDEV_EMULATION
        bool "Enable legacy fbdev support for your modesetting driver"
        depends on DRM && FB
-       depends on FB=y || DRM=m
+       depends on FB=y || DRM=m # DRM_KMS_FB_HELPER links against FB
        select DRM_KMS_HELPER
        select DRM_KMS_FB_HELPER
        default y

Let me know if you think those changes are sufficient

> With this fixed (assuming I am right):

> Reviewed-by: Sam Ravnborg <sam@ravnborg.org>


Thanks!

        Arnd
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Sam Ravnborg April 17, 2020, 8:29 p.m. | #3
Hi Arnd.

On Fri, Apr 17, 2020 at 10:03:23PM +0200, Arnd Bergmann wrote:
> On Fri, Apr 17, 2020 at 6:50 PM Sam Ravnborg <sam@ravnborg.org> wrote:

> 

> >

> > So what this try to say is that we cannot have FB a module while DRM is

> > built-in (marked N in the above).

> 

> Correct

> 

> >

> > Could you explain in the changelog why this combination is not good.

> > (Or tell me if my analysis was flawed).

> 

> I agree in hindsight this was less obvious than I thought ;-)

> 

> Added this text to the changelog:

> 

> |  When CONFIG_FB is a loadable module, DRM_KMS_FB_HELPER cannot be

> | part of the built-in subsystem, so add dependency to ensure this

> | can only be enabled if the DRM module can successfully be linked.

> 

> and this comment in the Kconfig file:

> 

> @@ -112,7 +112,7 @@ config DRM_DEBUG_DP_MST_TOPOLOGY_REFS

>  config DRM_FBDEV_EMULATION

>         bool "Enable legacy fbdev support for your modesetting driver"

>         depends on DRM && FB

> -       depends on FB=y || DRM=m

> +       depends on FB=y || DRM=m # DRM_KMS_FB_HELPER links against FB

>         select DRM_KMS_HELPER

>         select DRM_KMS_FB_HELPER

>         default y

> 

> Let me know if you think those changes are sufficient

> 

> > With this fixed (assuming I am right):

> > Reviewed-by: Sam Ravnborg <sam@ravnborg.org>


Yes, that explains it nicely - thanks.
But unless Daniel decides otherwise we do not get it applied.
He was not too happy with it.

	Sam
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Patch

diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
index 43594978958e..7c3109133685 100644
--- a/drivers/gpu/drm/Kconfig
+++ b/drivers/gpu/drm/Kconfig
@@ -80,7 +80,7 @@  config DRM_KMS_HELPER
 config DRM_KMS_FB_HELPER
 	bool
 	depends on DRM_KMS_HELPER
-	select FB
+	depends on FB
 	select FRAMEBUFFER_CONSOLE if !EXPERT
 	select FRAMEBUFFER_CONSOLE_DETECT_PRIMARY if FRAMEBUFFER_CONSOLE
 	select FB_SYS_FOPS
@@ -111,7 +111,8 @@  config DRM_DEBUG_DP_MST_TOPOLOGY_REFS
 
 config DRM_FBDEV_EMULATION
 	bool "Enable legacy fbdev support for your modesetting driver"
-	depends on DRM
+	depends on DRM && FB
+	depends on FB=y || DRM=m
 	select DRM_KMS_HELPER
 	select DRM_KMS_FB_HELPER
 	default y
diff --git a/drivers/gpu/drm/mxsfb/Kconfig b/drivers/gpu/drm/mxsfb/Kconfig
index 0dca8f27169e..33916b7b2c50 100644
--- a/drivers/gpu/drm/mxsfb/Kconfig
+++ b/drivers/gpu/drm/mxsfb/Kconfig
@@ -10,7 +10,6 @@  config DRM_MXSFB
 	depends on COMMON_CLK
 	select DRM_MXS
 	select DRM_KMS_HELPER
-	select DRM_KMS_FB_HELPER
 	select DRM_KMS_CMA_HELPER
 	select DRM_PANEL
 	help
diff --git a/drivers/gpu/drm/zte/Kconfig b/drivers/gpu/drm/zte/Kconfig
index 90ebaedc11fd..aa8594190b50 100644
--- a/drivers/gpu/drm/zte/Kconfig
+++ b/drivers/gpu/drm/zte/Kconfig
@@ -3,7 +3,6 @@  config DRM_ZTE
 	tristate "DRM Support for ZTE SoCs"
 	depends on DRM && ARCH_ZX
 	select DRM_KMS_CMA_HELPER
-	select DRM_KMS_FB_HELPER
 	select DRM_KMS_HELPER
 	select SND_SOC_HDMI_CODEC if SND_SOC
 	select VIDEOMODE_HELPERS