Some questions about DRM(Direct Rendering Manager)

InKi Dae daeinki at
Wed Jun 22 03:50:58 EDT 2011

It adds dri-devel at to this mail thread.
Thank you.

2011년 6월 22일 오후 3:04, daeinki <inki.dae at>님의 말:
> below is additional comments.
> daeinki 쓴 글:
>> Hi all,
>> I'm writing Samsung SoC based DRM framework and this one includes FIMD
>> and HDMI driver as hardware dependent modules. and for now, encoder,
>> connector, crtc and fb module has been materialized almost. but I'm
>> contending with  framebuffer setting issue(created fb_info should be
>> registered to linux framebuffer through register_framebuffer() or not)as
>> default framebuffer at booting time.
>> at drm_fb_helper_single_fb_probe() of drm_fb_helper.c file, fb_helper's
>> fb_probe callback is called and this one creates new framebuffer and
>> returns a value more then 0 if true. internally, this process creates an
>> fb_info object and drm_framebuffer and then drm_framebuffer would be
>> added to mode_config.fb_list of the drm_device.
> it's my mistake. return value is 0 if true, nonzero otherwise.
>> a value returned, new_fb is used to decide that it calls
>> register_framebuffer() or drm_fb_helper_set_par(). at this point, I am
>> confused it's a good way to call register_framebuffer() otherwise
>> drm_fb_helper_set_par(). if register_framebuffer() is called then I
>> guess drm_fb_helper_set_par() or drm_crtc_helper_set_config() should be
>> called somewhere subsequently to apply this one to real hardware because
>> previous process is just for maintaining data logically.(not set up data
>> to h/w)
>> it's a right way to call register_framebuffer() and then
>> drm_fb_helper_set_par() or drm_crtc_helper_set_config()? otherwise just
>> only drm_fb_helper_set_par() or drm_crtc_helper_set_config() ignoring
>> register_framebuffer()? and what is the purpose of using
>> register_framebuffer()?
> I understood that if fb_probe() callback is fail then fb_info object is
> registered to linux framebuffer through register_framebuffer()
> otherwise(if true) hardware configuration would be completed by
> drm_fb_helper_set_par() so the reason of using register_framebuffer() is
> that the case of failing fb_probe() callback, it is for drawing on only
> linux framebuffer. is it right?
>> In my case, first, register_framebuffer() is called and then if desired
>> default crtc id is matched with drm_fb_helper->crtc_info[0 ~ n].crtc_id,
>> it gets mode_set of drm_fb_helper->crtc_info[n] and then  it calls
>> drm_crtc_helper_set_config(mode_set). at this time, all the hardware
>> configurations would be completed.
>> thank you in advance.
>> Best Regards
>> Inki Dae.
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