From mboxrd@z Thu Jan 1 00:00:00 1970 From: Archit Taneja Date: Wed, 25 Mar 2015 08:29:54 +0000 Subject: Re: [RFC 1/6] drm: Add top level Kconfig option for DRM fbdev emulation Message-Id: <55126F32.90404@codeaurora.org> List-Id: References: <1425980493-27533-1-git-send-email-architt@codeaurora.org> <1425980493-27533-2-git-send-email-architt@codeaurora.org> <20150310094756.GE3800@phenom.ffwll.local> <54FEBEF1.5000103@codeaurora.org> <20150310100547.GG3800@phenom.ffwll.local> <54FEC5F1.90208@codeaurora.org> <20150310121702.GO3800@phenom.ffwll.local> <54FFFAEE.3020301@codeaurora.org> <20150311151731.GJ3800@phenom.ffwll.local> <550282C3.10903@codeaurora.org> <20150313090651.GZ3800@phenom.ffwll.local> In-Reply-To: <20150313090651.GZ3800@phenom.ffwll.local> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: robdclark@gmail.com, airlied@linux.ie, treding@nvidia.com, p.zabel@pengutronix.de, benjamin.gaignard@linaro.org, dri-devel@lists.freedesktop.org, daniel@ffwll.ch Cc: linux-arm-msm@vger.kernel.org, linux-fbdev@vger.kernel.org, tomi.valkeinen@ti.com, linux-kernel@vger.kernel.org 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 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 > #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? Archit -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project