Re: [RFC 1/6] drm: Add top level Kconfig option for DRM fbdev emulation
From: Archit Taneja
Date: Tue Jun 30 2015 - 03:56:41 EST
Hi,
On 06/30/2015 12:40 PM, Daniel Vetter wrote:
Any updates on this or too much distractions? I really think doing
this would be awesome for the drm subsystem, instead of reinventing
this wheel for each driver.
I'd started on this again. I've got more free time now than before, so I
should have something in a week or so. I agree it will help a lot (there
are already two new drivers since we started discussing this!)
Archit
-Daniel
On Wed, Mar 25, 2015 at 10:21 AM, Daniel Vetter <daniel@xxxxxxxx> wrote:
On Wed, Mar 25, 2015 at 01:47:54PM +0530, Archit Taneja wrote:
Hi,
On 03/13/2015 02:36 PM, Daniel Vetter wrote:
On Fri, Mar 13, 2015 at 11:55:07AM +0530, Archit Taneja wrote:
On 03/11/2015 08:47 PM, Daniel Vetter wrote:
On Wed, Mar 11, 2015 at 01:51:02PM +0530, Archit Taneja wrote:
On 03/10/2015 05:47 PM, Daniel Vetter wrote:
On Tue, Mar 10, 2015 at 03:52:41PM +0530, Archit Taneja wrote:
On 03/10/2015 03:35 PM, Daniel Vetter wrote:
On Tue, Mar 10, 2015 at 03:22:49PM +0530, Archit Taneja wrote:
On 03/10/2015 03:17 PM, Daniel Vetter wrote:
On Tue, Mar 10, 2015 at 03:11:28PM +0530, Archit Taneja wrote:
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.
Maybe clarify that for linux console support you also need
CONFIG_FRAMEBUFFER_CONSOLE? fbdev alone isn't enough.
DRM_KMS_FB_HELPER selects that for us, right?
Hm right I've missed that. Reminds me that you need one more patch at the
end to remove all the various select DRM_KMS_FB_HELPER from all drm
drivers. Otherwise this knob here won't work by default if you e.g. select
radeon. In general we can't mix explicit options with menu entries with a
select.
I was trying that out. Removing DRM_KMS_FB_HELPER and having
DRM_FBDEV_EMULATION disabled breaks drivers which use FB stuff internally in
their respective xyz_fbdev.c files.
But with the stubbed out functions that should work, right? Why doesn't
it?
There are still calls to functions from fb core like fb_set_suspend and
register_framebuffer which aren't covered by the drm fb helper functions.
Hm, sounds like we need another patch to stub out fb_set_suspend when
fbdev isn't enabled. Is there anything else?
There are a handful of fb core functions which are called by drm drivers:
fb_alloc_cmap/fb_dealloc_cmap
fb_sys_read/fb_sys_write
register_framebuffer/unregister_framebuffer/unlink_framebuffer/
remove_conflicting_framebuffers
fb_set_suspend
fb_deferred_io_init/fb_deferred_io_cleanup
framebuffer_alloc/framebuffer_release
Hm yeah that's somewhat annoying indeed. What about the following:
1. We move all the #include <linux/fb.h> from drivers into drm_fb_helper.h
2. Then we add stubs for these functions in drm_fb_helper.h, like this
#if defined(CONFIG_FB)
#include <linux/fb.h>
#else
/* static inline stubs for all the fb stuff used by kms drivers */
#endif
Imo this makes sense since kms drivers really have a bit a special
situation with fbdev. They're not full-blown fbdev drivers and can be
useful fully without fbdev.
I was trying this out. Removing 'linux/fb.h' and replacing stub fb funcs
won't really work because struct declarations(like fb_info) also get
removed.
I considered placing '#if IS_ENABLED(CONFIG_FB)' within linux/fb.h itself,
but that seemed a bit too intrusive.
This is what I'm currently doing:
- Some funcs, like framebufer_alloc/release, alloc_cmap/dealloc_cmap would
actually benefit if we have drm fb helpers for them. They are used in
exactly the same manner by all the drivers.
- For the rest of the functions that are sparsely used, I was considering
making very simple drm_fb_* wrapper functions. Something like:
void drm_fb_helper_deferred_io_init(struct drm_fb_helper *helper)
{
if (helper->fbdev)
fb_deferred_io_init(helper->fbdev);
}
We could have all fb calls called within drm_fb_helper.c, creating
drm_fb_helper_* stub functions would then be an easier task. What do you
think?
That's actually an option I considered, but I hoped we could do it with
less work. If this indeed works and you can create the patch that would be
awesome.
Thanks, Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
--
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project
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