From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg KH Subject: Re: [PATCH v1 2/2] drm/fb-helper: Ignore the value of fb_var_screeninfo.pixclock Date: Mon, 7 Jan 2019 11:12:55 +0100 Message-ID: <20190107101255.GA2364@kroah.com> References: <20181227231308.16904-1-mironov.ivan@gmail.com> <20181227231308.16904-3-mironov.ivan@gmail.com> <20181228120652.GR9058@dvetter-linux.ger.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: Received: from wout2-smtp.messagingengine.com (wout2-smtp.messagingengine.com [64.147.123.25]) by gabe.freedesktop.org (Postfix) with ESMTPS id 500896E425 for ; Mon, 7 Jan 2019 10:13:00 +0000 (UTC) Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" To: Ivan Mironov Cc: Maxime Ripard , Eugeniy Paltsev , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, 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Jan 2019 11:12:55 +0100 From: Greg KH To: Ivan Mironov Cc: Daniel Vetter , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Maarten Lankhorst , Maxime Ripard , Sean Paul , David Airlie , saahriktu , Eugeniy Paltsev Subject: Re: [PATCH v1 2/2] drm/fb-helper: Ignore the value of fb_var_screeninfo.pixclock Message-ID: <20190107101255.GA2364@kroah.com> References: <20181227231308.16904-1-mironov.ivan@gmail.com> <20181227231308.16904-3-mironov.ivan@gmail.com> <20181228120652.GR9058@dvetter-linux.ger.corp.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Jan 05, 2019 at 09:21:21PM +0500, Ivan Mironov wrote: > On Fri, 2018-12-28 at 13:06 +0100, Daniel Vetter wrote: > > On Fri, Dec 28, 2018 at 04:13:08AM +0500, Ivan Mironov wrote: > > > Strict requirement of pixclock to be zero breaks support of SDL 1.2 > > > which contains hardcoded table of supported video modes with non-zero > > > pixclock values[1]. > > > > > > To better understand which pixclock values are considered valid and how > > > driver should handle these values, I briefly examined few existing fbdev > > > drivers and documentation in Documentation/fb/. And it looks like there > > > are no strict rules on that and actual behaviour varies: > > > > > > * some drivers treat (pixclock == 0) as "use defaults" (uvesafb.c); > > > * some treat (pixclock == 0) as invalid value which leads to > > > -EINVAL (clps711x-fb.c); > > > * some pass converted pixclock value to hardware (uvesafb.c); > > > * some are trying to find nearest value from predefined table > > > (vga16fb.c, video_gx.c). > > > > > > Given this, I believe that it should be safe to just ignore this value if > > > changing is not supported. It seems that any portable fbdev application > > > which was not written only for one specific device working under one > > > specific kernel version should not rely on any particular behaviour of > > > pixclock anyway. > > > > > > However, while enabling SDL1 applications to work out of the box when > > > there is no /etc/fb.modes with valid settings, this change affects the > > > video mode choosing logic in SDL. Depending on current screen > > > resolution, contents of /etc/fb.modes and resolution requested by > > > application, this may lead to user-visible difference (not always): > > > image will be displayed in a right way, but it will be aligned to the > > > left instead of center. There is no "right behaviour" here as well, as > > > emulated fbdev, opposing to old fbdev drivers, simply ignores any > > > requsts of video mode changes with resolutions smaller than current. > > > > > > Feel free to NAK this patch if you think that it causes breakage of > > > user-space =). > > > > It's a regression, we don't nack regression fixes :-) > > > > > The easiest way to reproduce this problem is to install sdl-sopwith[2], > > > remove /etc/fb.modes file if it exists, and then try to run sopwith > > > from console without X. At least in Fedora 29, sopwith may be simply > > > installed from standard repositories. > > > > > > [1] SDL 1.2.15 source code, src/video/fbcon/SDL_fbvideo.c, vesa_timings > > > [2] http://sdl-sopwith.sourceforge.net/ > > > > > > Signed-off-by: Ivan Mironov > > > > I thought this is also a regression fix, so also needs Fixes: and cc: > > stable? > > -Daniel > > This particular patch fixes a bug that existed for 10 years unnoticed. > Are "Fixes:" and "Cc: stable" really required? If you want it backported into a stable kernel release, then yes, they are needed :) thanks, greg k-h