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[212.51.149.33]) by smtp.gmail.com with ESMTPSA id ji12-20020a170907980c00b0094e1272bd12sm640044ejc.159.2023.04.13.01.54.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Apr 2023 01:54:27 -0700 (PDT) Date: Thu, 13 Apr 2023 10:54:26 +0200 From: Daniel Vetter To: Helge Deller Cc: Daniel Vetter , Thomas Zimmermann , javierm@redhat.com, daniel.vetter@ffwll.ch, patrik.r.jakobsson@gmail.com, dri-devel@lists.freedesktop.org, Daniel Vetter , linux-fbdev@vger.kernel.org, Bjorn Helgaas , linux-pci@vger.kernel.org Subject: Re: [PATCH v5 2/9] video/aperture: use generic code to figure out the vga default device Message-ID: References: <20230406132109.32050-1-tzimmermann@suse.de> <20230406132109.32050-3-tzimmermann@suse.de> <85282243-33a6-a311-0b50-a7edfc4c4c6e@gmx.de> <83acd60f-4a42-25a9-afee-ca7919ee42a9@gmx.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <83acd60f-4a42-25a9-afee-ca7919ee42a9@gmx.de> X-Operating-System: Linux phenom 6.1.0-7-amd64 Precedence: bulk List-ID: X-Mailing-List: linux-fbdev@vger.kernel.org On Tue, Apr 11, 2023 at 05:25:47PM +0200, Helge Deller wrote: > On 4/11/23 16:36, Daniel Vetter wrote: > > On Fri, Apr 07, 2023 at 10:54:00PM +0200, Helge Deller wrote: > > > On 4/6/23 15:21, Thomas Zimmermann wrote: > > > > From: Daniel Vetter > > > > > > > > Since vgaarb has been promoted to be a core piece of the pci subsystem > > > > we don't have to open code random guesses anymore, we actually know > > > > this in a platform agnostic way, and there's no need for an x86 > > > > specific hack. See also commit 1d38fe6ee6a8 ("PCI/VGA: Move vgaarb to > > > > drivers/pci") > > > > > > > > This should not result in any functional change, and the non-x86 > > > > multi-gpu pci systems are probably rare enough to not matter (I don't > > > > know of any tbh). But it's a nice cleanup, so let's do it. > > > > > > > > There's been a few questions on previous iterations on dri-devel and > > > > irc: > > > > > > > > - fb_is_primary_device() seems to be yet another implementation of > > > > this theme, and at least on x86 it checks for both > > > > vga_default_device OR rom shadowing. There shouldn't ever be a case > > > > where rom shadowing gives any additional hints about the boot vga > > > > device, but if there is then the default vga selection in vgaarb > > > > should probably be fixed. And not special-case checks replicated all > > > > over. > > > > > > > > - Thomas also brought up that on most !x86 systems > > > > fb_is_primary_device() returns 0, except on sparc/parisc. But these > > > > 2 special cases are about platform specific devices and not pci, so > > > > shouldn't have any interactions. > > > > > > Nearly all graphics cards on parisc machines are actually PCI cards, > > > but the way we handle the handover to graphics mode with STIcore doesn't > > > conflicts with your planned aperture changes. > > > So no problem as far as I can see for parisc... > > > > Ah I thought sticore was some very special bus, if those can be pci cards > > STI stands for "Standard Text Interface" [1], which is a API of ROM functions > to output text chars on a console. It's comparable to the text output functions > in a PC-BIOS on x86 and dependend on the ROM it drives any supported card which has > a parisc ROM. So, STI supports cards on PCI & AGP busses, as well on older GSC busses. > [1] https://parisc.wiki.kernel.org/images-parisc/e/e3/Sti.pdf > > > underneath then I guess some cleanup eventually might be a good idea? For > > anything with a pci bus it's rather strange when vgaarb and > > fb_is_primary_device() aren't a match ... > > There is no VGA on parisc, so there is no conflict. Cards come either with > a parisc STI ROM to support text mode, or they will only be used as secondary > cards only. The graphics mode is only done in userspace by specific drivers, e.g. > by the X11 server in HP-UX. > Even on x86 the BIOS will only show text output if the graphics card comes > with a VGA-compatible BIOS. tbf after reading vt.c and fbcon.c some more I'm pretty sure my patch is nonsense. As sure as you can be with vt/fbcon :-/ Since it sounds like it's a driver bug, maybe a patch to do a pr_warn in register_framebuffer if there's no mode? I read a pile of code around modedb.c right now, and there's a lot of things that silently assume that you always have a mode. So would be good thing to check. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch