Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753769AbcD0Jpj (ORCPT ); Wed, 27 Apr 2016 05:45:39 -0400 Received: from smtp.domeneshop.no ([194.63.252.55]:35786 "EHLO smtp.domeneshop.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753700AbcD0Jpf (ORCPT ); Wed, 27 Apr 2016 05:45:35 -0400 Subject: Re: [PATCH v2 4/8] drm/fb-helper: Add fb_deferred_io support To: dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, laurent.pinchart@ideasonboard.com, tomi.valkeinen@ti.com, linux-kernel@vger.kernel.org References: <1461530942-22485-1-git-send-email-noralf@tronnes.org> <1461530942-22485-5-git-send-email-noralf@tronnes.org> <20160425090957.GQ2510@phenom.ffwll.local> <571F9656.1090506@tronnes.org> <20160426171902.GA2558@phenom.ffwll.local> From: =?UTF-8?Q?Noralf_Tr=c3=b8nnes?= Message-ID: <57208A3B.4020909@tronnes.org> Date: Wed, 27 Apr 2016 11:45:31 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.7.1 MIME-Version: 1.0 In-Reply-To: <20160426171902.GA2558@phenom.ffwll.local> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5952 Lines: 127 Den 26.04.2016 19:19, skrev Daniel Vetter: > On Tue, Apr 26, 2016 at 06:24:54PM +0200, Noralf Tr?nnes wrote: >> Den 25.04.2016 11:09, skrev Daniel Vetter: >>> On Sun, Apr 24, 2016 at 10:48:58PM +0200, Noralf Tr?nnes wrote: >>>> This adds deferred io support if CONFIG_FB_DEFERRED_IO is enabled. >>>> The fbdev framebuffer changes are flushed using the callback >>>> (struct drm_framebuffer *)->funcs->dirty() by a dedicated worker >>>> ensuring that it always runs in process context. >>>> >>>> Signed-off-by: Noralf Tr?nnes >>>> --- >>>> >>>> Changes since v1: >>>> - Use a dedicated worker to run the framebuffer flushing like qxl does >>>> - Add parameter descriptions to drm_fb_helper_deferred_io >>>> >>>> drivers/gpu/drm/drm_fb_helper.c | 127 +++++++++++++++++++++++++++++++++++++++- >>>> include/drm/drm_fb_helper.h | 17 ++++++ >>>> 2 files changed, 143 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c >>>> index 855108e..46ee6f8 100644 >>>> --- a/drivers/gpu/drm/drm_fb_helper.c >>>> +++ b/drivers/gpu/drm/drm_fb_helper.c >>>> @@ -40,6 +40,7 @@ >>>> #include >>>> #include >>>> #include >>>> +#include >>>> >>>> static bool drm_fbdev_emulation = true; >>>> module_param_named(fbdev_emulation, drm_fbdev_emulation, bool, 0600); >>>> @@ -48,6 +49,10 @@ MODULE_PARM_DESC(fbdev_emulation, >>>> >>>> static LIST_HEAD(kernel_fb_helper_list); >>>> >>>> +static void drm_fb_helper_dirty_init(struct drm_fb_helper *helper); >>>> +static void drm_fb_helper_dirty(struct fb_info *info, u32 x, u32 y, >>>> + u32 width, u32 height); >>>> + >>>> /** >>>> * DOC: fbdev helpers >>>> * >>>> @@ -84,6 +89,16 @@ static LIST_HEAD(kernel_fb_helper_list); >>>> * and set up an initial configuration using the detected hardware, drivers >>>> * should call drm_fb_helper_single_add_all_connectors() followed by >>>> * drm_fb_helper_initial_config(). >>>> + * >>>> + * If CONFIG_FB_DEFERRED_IO is enabled and >>>> + * (struct drm_framebuffer *)->funcs->dirty is set, the >>>> + * drm_fb_helper_{cfb,sys}_{write,fillrect,copyarea,imageblit} functions >>>> + * will accumulate changes and schedule (struct fb_helper).dirty_work to run >>>> + * right away. This worker then calls the dirty() function ensuring that it >>>> + * will always run in process context since the fb_*() function could be >>>> + * running in atomic context. If drm_fb_helper_deferred_io() is used as the >>>> + * deferred_io callback it will also schedule dirty_work with the damage >>>> + * collected from the mmap page writes. >>> One thing to consider (and personally I don't care either way) is whether >>> we shouldn't just select CONFIG_FB_DEFERRED_IO if the fbdev helpers are >>> enabled. Pushing that out to drivers is imo a bit fragile. >>> >>> But like I said I'm ok with either way. >> My concern was adding code and data that only a few drivers would >> actually use. But of course there's the tradeoff with complexity. >> I use this to enable it: >> select FB_DEFERRED_IO if DRM_KMS_FB_HELPER >> >> I guess the maintainer has to make this choice between size and complexity >> :-) >> I can enable it by default if you want, drm is both huge and complex so I >> don't know what's best. >> >> As a sidenote, I have also put all the fbdev code in a file of it's own to >> make it simple with regards to the DRM_FBDEV_EMULATION user option: >> tinydrm-$(CONFIG_DRM_KMS_FB_HELPER) += tinydrm-fbdev.o > Ok, if you ask maintainers then please nuke the #ifdef from .c files. If > you select CONFIG_DRM_KMS_FB_HELPER, then you get hdmi, edid, dp aux, dp > mst and whatever else helpers, even if you don't need them. Adding 3 > functions for defio when you select fbdev helpers and maybe don't need > them is totally harmless. And removing the #ifdef will look so much better > ;-) Will do :-) Kernel development is just my hobby so I'm not well versed in all of this. >>>> */ >>>> >>>> /** >>>> @@ -401,11 +416,14 @@ backoff: >>>> static int restore_fbdev_mode(struct drm_fb_helper *fb_helper) >>>> { >>>> struct drm_device *dev = fb_helper->dev; >>>> + struct fb_info *info = fb_helper->fbdev; >>>> struct drm_plane *plane; >>>> int i; >>>> >>>> drm_warn_on_modeset_not_all_locked(dev); >>>> >>>> + drm_fb_helper_dirty(info, 0, 0, info->var.xres, info->var.yres); >>> Why is this needed? If you do a modeset (or pageflip or whatever) drivers >>> are supposed to re-upload the entire screen. We've talked about adding a >>> dirty rectangle to atomic to allow userspace to optimize this, but there >>> should _never_ be a need to do a dirtyfb call around a modeset. Probably >>> just a driver bug in your panel drm drivers? >> Ok, in tinydrm I now set a flag in &drm_simple_display_pipe_funcs >> ->plane_update to indicate that the next dirty() should do the whole >> framebuffer which seems to work fine. >> Should I actually perform the update as well? >> If so I would need to add a worker in tinydrm to do that. > Yes, plane update should always do a full update. Not sure how you get > away with delaying that to ->dirty, maybe modesetting isn't > double-buffering when you don't have a GL that could do glamour. > > ->dirty is _only_ for frontbuffer rendering, not for page-flipping to an > entirely new buffer. In short if someone calls ->dirty on a buffer which > is currently not being displayed than a) they're silly b) drivers should > treat it as a no-op. Maybe we need a helper to do that ... > -Daniel drm_fb_helper will call dirty() as long as there's fbdev activity, so the driver needs to take that into account. For instance fbcon with a blinking cursor will trigger calls even if a buffer has been set up on the drm side. tinydrm checks the fb against the fb set on the plane and if it differs it's a no-op. Noralf.