Re: [RFC 1/6] drm: Add top level Kconfig option for DRM fbdev emulation

[Archit Taneja]

On 03/10/2015 03:16 PM, Daniel Vetter wrote:
> On Tue, Mar 10, 2015 at 03:11:28PM +0530, Archit Taneja wrote:
> > Legacy fbdev emulation support via DRM is achieved through KMS FB helpers.
> > Most modesetting drivers enable provide fbdev emulation by default by selecting
> > KMS FB helpers. A few provide a separate Kconfig option for the user to enable
> > or disbale fbdev emulation.
> >
> > Enabling fbdev emulation is finally a distro-level decision. Having a top level
> > Kconfig option for fbdev emulation helps by providing a uniform way to
> > enable/disable fbdev emulation for any modesetting driver. It also lets us
> > remove unnecessary driver specific Kconfig options that causes bloat.
> >
> > With a top level Kconfig in place, we can stub out the fb helper functions when
> > not needed without breaking functionality. Having stub functions also prevents
> > drivers to require wrapping fb helper function calls with #ifdefs.
> >
> > DRM_FBDEV_EMULATION defaults to y since many drivers enable fbdev emulation by
> > default and majority of distributions expect the fbdev interface in the kernel.
> >
> > For now, this config selects both FB_SYS_* and FB_CFB_* configs as some
> > modesetting drivers use the former and other the later. This needs to be taken
> > care of in a better way.
> >
> > Signed-off-by: Archit Taneja <architt@xxxxxxxxxxxxxx>
> > ---
> >   drivers/gpu/drm/Kconfig     |  18 +++++++
> >   drivers/gpu/drm/Makefile    |   4 ++
> >   include/drm/drm_fb_helper.h | 120 ++++++++++++++++++++++++++++++++++++++++++++
> >   3 files changed, 142 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> > index 151a050..38f83a0 100644
> > --- a/drivers/gpu/drm/Kconfig
> > +++ b/drivers/gpu/drm/Kconfig
> > @@ -40,6 +40,24 @@ config DRM_KMS_FB_HELPER
> >   	help
> >   	  FBDEV helpers for KMS drivers.
> >
> > +config DRM_FBDEV_EMULATION
> > +	bool "Enable legacy fbdev support for your modesetting driver"
> > +	depends on DRM
> > +	select DRM_KMS_HELPER
> > +	select DRM_KMS_FB_HELPER
> > +	select FB_SYS_FILLRECT
> > +	select FB_SYS_COPYAREA
> > +	select FB_SYS_IMAGEBLIT
> > +	select FB_SYS_FOPS
> > +	select FB_CFB_FILLRECT
> > +	select FB_CFB_COPYAREA
> > +	select FB_CFB_IMAGEBLIT
> > +	default y
> > +	help
> > +	  Choose this option if you have a need for the legacy fbdev
> > +	  support. Note that this support also provide the linux console
> > +	  support on top of your modesetting driver.
> > +
> >   config DRM_LOAD_EDID_FIRMWARE
> >   	bool "Allow to specify an EDID data set instead of probing for it"
> >   	depends on DRM_KMS_HELPER
> > diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> > index 2c239b9..c1d44b2 100644
> > --- a/drivers/gpu/drm/Makefile
> > +++ b/drivers/gpu/drm/Makefile
> > @@ -25,7 +25,11 @@ drm-$(CONFIG_OF) += drm_of.o
> >   drm_kms_helper-y := drm_crtc_helper.o drm_dp_helper.o drm_probe_helper.o \
> >   		drm_plane_helper.o drm_dp_mst_topology.o drm_atomic_helper.o
> >   drm_kms_helper-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o
> > +
> > +ifeq ($(CONFIG_DRM_FBDEV_EMULATION),y)
> >   drm_kms_helper-$(CONFIG_DRM_KMS_FB_HELPER) += drm_fb_helper.o
> > +endif
>
> This should work as
>
> drm_kms_helper-$CONFIG_DRM_FBDEV_EMULATION += drm_fb_helper.o
>
> since both <modename>-y and <modename>-m are merged together.

Ah right. I'll fix that.

Archit

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