From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A4A8DC433FE for ; Tue, 5 Apr 2022 13:24:57 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id C0CC910E902; Tue, 5 Apr 2022 13:24:56 +0000 (UTC) Received: from mail-qt1-f170.google.com (mail-qt1-f170.google.com [209.85.160.170]) by gabe.freedesktop.org (Postfix) with ESMTPS id AF65710E905; Tue, 5 Apr 2022 13:24:55 +0000 (UTC) Received: by mail-qt1-f170.google.com with SMTP id b18so10894182qtk.13; Tue, 05 Apr 2022 06:24:55 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=hBCPhJo5YyS6XSPC6qSR2NczndtrlVmfcRjGORmxI/A=; b=DQ0ovByA1YEDF2Qxk3uOjxB06EnbFTDJRFD3IITrbG6YX9SGT3A68IdJr2fx1f8G6a lR/pWm9IdxYcycEV83K/WHomgeVSpKUoAGtrDssfBQVVkHVyZC3VHe7uGOhT+bRzfYvo 0WMLFoDoy7Nr+ky5cwkvjYgKp/vo+I65GQbXmhtp5PERoEdqJngJBKNbZLpn7gbOrk1p BMoM7NQM4Kq5bS1Iyk8v3X4dc6l19S6+spNIyppVwbvY2QPR8EXCPu8CHc4M2vpFZ/3b ebzhgDwT1UspTfGGdfFbw31nR0KidZeuaYYi8QxtumX14Uy/nT4fcrHGfnhPvDqypEwc uZJw== X-Gm-Message-State: AOAM531AnawFKkfVbt19OrlPVLCAijMtLNj21mg7tJ+EeT9IJXqgcJ7y 5m17ss2WUPPzAFvvNWKGwWqIe9KsVLHQQw== X-Google-Smtp-Source: ABdhPJyVlxjAHfAcWHZ6udh/swia7X/HPDbpZYnCiTmAUhp4opkb7saHxZskWQ5CwgJjwl5qbPmH2A== X-Received: by 2002:a05:620a:2585:b0:680:f1f5:23ac with SMTP id x5-20020a05620a258500b00680f1f523acmr2126899qko.656.1649165093847; Tue, 05 Apr 2022 06:24:53 -0700 (PDT) Received: from mail-yw1-f180.google.com (mail-yw1-f180.google.com. [209.85.128.180]) by smtp.gmail.com with ESMTPSA id l8-20020a05622a174800b002e1e3f7d4easm11459454qtk.86.2022.04.05.06.24.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 05 Apr 2022 06:24:52 -0700 (PDT) Received: by mail-yw1-f180.google.com with SMTP id 00721157ae682-2db2add4516so135941807b3.1; Tue, 05 Apr 2022 06:24:52 -0700 (PDT) X-Received: by 2002:a81:618b:0:b0:2db:d952:8a39 with SMTP id v133-20020a81618b000000b002dbd9528a39mr2679880ywb.132.1649165091759; Tue, 05 Apr 2022 06:24:51 -0700 (PDT) MIME-Version: 1.0 References: <20220208210824.2238981-1-daniel.vetter@ffwll.ch> <20220208210824.2238981-19-daniel.vetter@ffwll.ch> <4ae20b63-f452-fdb4-ced6-d4968a8d69f0@redhat.com> <408ffe9b-f09f-dc7e-7f5e-a93b311a06fa@redhat.com> In-Reply-To: From: Geert Uytterhoeven Date: Tue, 5 Apr 2022 15:24:40 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2 18/19] Revert "fbdev: Prevent probing generic drivers if a FB is already registered" To: Daniel Vetter Content-Type: text/plain; charset="UTF-8" X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Linux Fbdev development list , Greg KH , Intel Graphics Development , LKML , DRI Development , Javier Martinez Canillas , Hans de Goede , Peter Jones , Thomas Zimmermann , Ilya Trukhanov , Daniel Vetter Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Hi Daniel, On Tue, Apr 5, 2022 at 1:48 PM Daniel Vetter wrote: > On Tue, 5 Apr 2022 at 11:52, Javier Martinez Canillas > wrote: > > On 4/5/22 11:24, Daniel Vetter wrote: > > > On Tue, 5 Apr 2022 at 11:19, Javier Martinez Canillas > > >> This is how I think that work, please let me know if you see something > > >> wrong in my logic: > > >> > > >> 1) A PCI device of OF device is registered for the GPU, this attempt to > > >> match a registered driver but no driver was registered that match yet. > > >> > > >> 2) The efifb driver is built-in, will be initialized according to the link > > >> order of the objects under drivers/video and the fbdev driver is registered. > > >> > > >> There is no platform device or PCI/OF device registered that matches. > > >> > > >> 3) The DRM driver is built-in, will be initialized according to the link > > >> order of the objects under drivers/gpu and the DRM driver is registered. > > >> > > >> This matches the device registered in (1) and the DRM driver probes. > > >> > > >> 4) The DRM driver .probe kicks out any conflicting DRM drivers and pdev > > >> before registering the DRM device. > > >> > > >> There are no conflicting drivers or platform device at this point. > > >> > > >> 5) Latter at some point the drivers/firmware/sysfb.c init function is > > >> executed, and this registers a platform device for the generic fb. > > >> > > >> This device matches the efifb driver registered in (2) and the fbdev > > >> driver probes. > > >> > > >> Since that happens *after* the DRM driver already matched, probed > > >> and registered the DRM device, that is a bug and what the reverted > > >> patch worked around. > > >> > > >> So we need to prevent (5) if (1) and (3) already happened. Having a flag > > >> set in the fbdev core somewhere when remove_conflicting_framebuffers() > > >> is called could be a solution indeed. > > >> > > >> That is, the fbdev core needs to know that a DRM driver already probed > > >> and make register_framebuffer() fail if info->flag & FBINFO_MISC_FIRMWARE > > >> > > >> I can attempt to write a patch for that. > > > > > > Ah yeah that could be an issue. I think the right fix is to replace > > > the platform dev unregister with a sysfb_unregister() function in > > > sysfb.c, which is synced with a common lock with the sysfb_init > > > function and a small boolean. I think I can type that up quickly for > > > v3. > > > > It's more complicated than that since sysfb is just *one* of the several > > places where platform devices can be registered for video devices. > > > > For instance, the vga16fb driver registers its own platform device in > > its module_init() function so that can also happen after the conflicting > > framebuffers (and associated devices) were removed by a DRM driver probe. > > > > I tried to minimize the issue for that particular driver with commit: > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0499f419b76f > > > > But the point stands, it all boils down to the fact that you have two > > different subsystems registering video drivers and they don't know all > > about each other to take a proper decision. > > > > Right now the drm_aperture_remove_conflicting_framebuffers() call signals > > in one direction from DRM to fbdev but there isn't a communication in the > > other direction, from fbdev to DRM. > > > > I believe the correct fix would be for the fbdev core to keep a list of > > the apertures struct that are passed to remove_conflicting_framebuffers(), > > that way it will know what apertures are not available anymore and prevent > > to register any fbdev framebuffer that conflicts with one already present. > > Hm that still feels like reinventing a driver model, badly. > > I think there's two cleaner solutions: > - move all the firmware driver platform_dev into sysfb.c, and then > just bind the special cases against that (e.g. offb, vga16fb and all > these). Then we'd have one sysfb_try_unregister(struct device *dev) > interface that fbmem.c uses. > - let fbmem.c call into each of these firmware device providers, which > means some loops most likely (like we can't call into vga16fb), so > probably need to move that into fbmem.c and it all gets a bit messy. > > > Let me know if you think that makes sense and I can attempt to write a fix. > > I still think unregistering the platform_dev properly makes the most That doesn't sound very driver-model-aware to me. The device is what the driver binds to; it does not cease to exist. > sense, and feels like the most proper linux device model solution > instead of hacks on top - if the firmware fb is unuseable because a > native driver has taken over, we should nuke that. And also the > firmware fb driver would then just bind to that platform_dev if it > exists, and only if it exists. Also I think it should be the > responsibility of whichever piece of code that registers these > platform devices to ensure that platform_dev actually still exists. > That's why I think pushing all that code into sysfb.c is probably the > cleanest solution. Can't you unbind the generic driver first, and bind the specific driver afterwards? Alike writing to sysfs unbind/driver_override/bind, but from code? Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 1798EC433EF for ; Tue, 5 Apr 2022 13:24:57 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 8A31710E905; Tue, 5 Apr 2022 13:24:56 +0000 (UTC) Received: from mail-qt1-f170.google.com (mail-qt1-f170.google.com [209.85.160.170]) by gabe.freedesktop.org (Postfix) with ESMTPS id AF65710E905; Tue, 5 Apr 2022 13:24:55 +0000 (UTC) Received: by mail-qt1-f170.google.com with SMTP id b18so10894182qtk.13; Tue, 05 Apr 2022 06:24:55 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=hBCPhJo5YyS6XSPC6qSR2NczndtrlVmfcRjGORmxI/A=; b=DQ0ovByA1YEDF2Qxk3uOjxB06EnbFTDJRFD3IITrbG6YX9SGT3A68IdJr2fx1f8G6a lR/pWm9IdxYcycEV83K/WHomgeVSpKUoAGtrDssfBQVVkHVyZC3VHe7uGOhT+bRzfYvo 0WMLFoDoy7Nr+ky5cwkvjYgKp/vo+I65GQbXmhtp5PERoEdqJngJBKNbZLpn7gbOrk1p BMoM7NQM4Kq5bS1Iyk8v3X4dc6l19S6+spNIyppVwbvY2QPR8EXCPu8CHc4M2vpFZ/3b ebzhgDwT1UspTfGGdfFbw31nR0KidZeuaYYi8QxtumX14Uy/nT4fcrHGfnhPvDqypEwc uZJw== X-Gm-Message-State: AOAM531AnawFKkfVbt19OrlPVLCAijMtLNj21mg7tJ+EeT9IJXqgcJ7y 5m17ss2WUPPzAFvvNWKGwWqIe9KsVLHQQw== X-Google-Smtp-Source: ABdhPJyVlxjAHfAcWHZ6udh/swia7X/HPDbpZYnCiTmAUhp4opkb7saHxZskWQ5CwgJjwl5qbPmH2A== X-Received: by 2002:a05:620a:2585:b0:680:f1f5:23ac with SMTP id x5-20020a05620a258500b00680f1f523acmr2126899qko.656.1649165093847; Tue, 05 Apr 2022 06:24:53 -0700 (PDT) Received: from mail-yw1-f180.google.com (mail-yw1-f180.google.com. [209.85.128.180]) by smtp.gmail.com with ESMTPSA id l8-20020a05622a174800b002e1e3f7d4easm11459454qtk.86.2022.04.05.06.24.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 05 Apr 2022 06:24:52 -0700 (PDT) Received: by mail-yw1-f180.google.com with SMTP id 00721157ae682-2db2add4516so135941807b3.1; Tue, 05 Apr 2022 06:24:52 -0700 (PDT) X-Received: by 2002:a81:618b:0:b0:2db:d952:8a39 with SMTP id v133-20020a81618b000000b002dbd9528a39mr2679880ywb.132.1649165091759; Tue, 05 Apr 2022 06:24:51 -0700 (PDT) MIME-Version: 1.0 References: <20220208210824.2238981-1-daniel.vetter@ffwll.ch> <20220208210824.2238981-19-daniel.vetter@ffwll.ch> <4ae20b63-f452-fdb4-ced6-d4968a8d69f0@redhat.com> <408ffe9b-f09f-dc7e-7f5e-a93b311a06fa@redhat.com> In-Reply-To: From: Geert Uytterhoeven Date: Tue, 5 Apr 2022 15:24:40 +0200 X-Gmail-Original-Message-ID: Message-ID: To: Daniel Vetter Content-Type: text/plain; charset="UTF-8" Subject: Re: [Intel-gfx] [PATCH v2 18/19] Revert "fbdev: Prevent probing generic drivers if a FB is already registered" X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Linux Fbdev development list , Greg KH , Intel Graphics Development , LKML , DRI Development , Javier Martinez Canillas , Peter Jones , Thomas Zimmermann , Ilya Trukhanov , Daniel Vetter , Zack Rusin Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" Hi Daniel, On Tue, Apr 5, 2022 at 1:48 PM Daniel Vetter wrote: > On Tue, 5 Apr 2022 at 11:52, Javier Martinez Canillas > wrote: > > On 4/5/22 11:24, Daniel Vetter wrote: > > > On Tue, 5 Apr 2022 at 11:19, Javier Martinez Canillas > > >> This is how I think that work, please let me know if you see something > > >> wrong in my logic: > > >> > > >> 1) A PCI device of OF device is registered for the GPU, this attempt to > > >> match a registered driver but no driver was registered that match yet. > > >> > > >> 2) The efifb driver is built-in, will be initialized according to the link > > >> order of the objects under drivers/video and the fbdev driver is registered. > > >> > > >> There is no platform device or PCI/OF device registered that matches. > > >> > > >> 3) The DRM driver is built-in, will be initialized according to the link > > >> order of the objects under drivers/gpu and the DRM driver is registered. > > >> > > >> This matches the device registered in (1) and the DRM driver probes. > > >> > > >> 4) The DRM driver .probe kicks out any conflicting DRM drivers and pdev > > >> before registering the DRM device. > > >> > > >> There are no conflicting drivers or platform device at this point. > > >> > > >> 5) Latter at some point the drivers/firmware/sysfb.c init function is > > >> executed, and this registers a platform device for the generic fb. > > >> > > >> This device matches the efifb driver registered in (2) and the fbdev > > >> driver probes. > > >> > > >> Since that happens *after* the DRM driver already matched, probed > > >> and registered the DRM device, that is a bug and what the reverted > > >> patch worked around. > > >> > > >> So we need to prevent (5) if (1) and (3) already happened. Having a flag > > >> set in the fbdev core somewhere when remove_conflicting_framebuffers() > > >> is called could be a solution indeed. > > >> > > >> That is, the fbdev core needs to know that a DRM driver already probed > > >> and make register_framebuffer() fail if info->flag & FBINFO_MISC_FIRMWARE > > >> > > >> I can attempt to write a patch for that. > > > > > > Ah yeah that could be an issue. I think the right fix is to replace > > > the platform dev unregister with a sysfb_unregister() function in > > > sysfb.c, which is synced with a common lock with the sysfb_init > > > function and a small boolean. I think I can type that up quickly for > > > v3. > > > > It's more complicated than that since sysfb is just *one* of the several > > places where platform devices can be registered for video devices. > > > > For instance, the vga16fb driver registers its own platform device in > > its module_init() function so that can also happen after the conflicting > > framebuffers (and associated devices) were removed by a DRM driver probe. > > > > I tried to minimize the issue for that particular driver with commit: > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0499f419b76f > > > > But the point stands, it all boils down to the fact that you have two > > different subsystems registering video drivers and they don't know all > > about each other to take a proper decision. > > > > Right now the drm_aperture_remove_conflicting_framebuffers() call signals > > in one direction from DRM to fbdev but there isn't a communication in the > > other direction, from fbdev to DRM. > > > > I believe the correct fix would be for the fbdev core to keep a list of > > the apertures struct that are passed to remove_conflicting_framebuffers(), > > that way it will know what apertures are not available anymore and prevent > > to register any fbdev framebuffer that conflicts with one already present. > > Hm that still feels like reinventing a driver model, badly. > > I think there's two cleaner solutions: > - move all the firmware driver platform_dev into sysfb.c, and then > just bind the special cases against that (e.g. offb, vga16fb and all > these). Then we'd have one sysfb_try_unregister(struct device *dev) > interface that fbmem.c uses. > - let fbmem.c call into each of these firmware device providers, which > means some loops most likely (like we can't call into vga16fb), so > probably need to move that into fbmem.c and it all gets a bit messy. > > > Let me know if you think that makes sense and I can attempt to write a fix. > > I still think unregistering the platform_dev properly makes the most That doesn't sound very driver-model-aware to me. The device is what the driver binds to; it does not cease to exist. > sense, and feels like the most proper linux device model solution > instead of hacks on top - if the firmware fb is unuseable because a > native driver has taken over, we should nuke that. And also the > firmware fb driver would then just bind to that platform_dev if it > exists, and only if it exists. Also I think it should be the > responsibility of whichever piece of code that registers these > platform devices to ensure that platform_dev actually still exists. > That's why I think pushing all that code into sysfb.c is probably the > cleanest solution. Can't you unbind the generic driver first, and bind the specific driver afterwards? Alike writing to sysfs unbind/driver_override/bind, but from code? Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EF766C433FE for ; Wed, 6 Apr 2022 00:27:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1588996AbiDFASG (ORCPT ); Tue, 5 Apr 2022 20:18:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48790 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243622AbiDEPJY (ORCPT ); Tue, 5 Apr 2022 11:09:24 -0400 Received: from mail-qt1-f171.google.com (mail-qt1-f171.google.com [209.85.160.171]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0E64ABF53A; Tue, 5 Apr 2022 06:24:55 -0700 (PDT) Received: by mail-qt1-f171.google.com with SMTP id o15so9548925qtv.8; Tue, 05 Apr 2022 06:24:55 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=hBCPhJo5YyS6XSPC6qSR2NczndtrlVmfcRjGORmxI/A=; b=EURQlCOo5uMFEGKK2235tNRMwsSYU4ycAr5/uhPDmTcoSJCkr8q77DmULI8+dVOW5U Fg7viLWjfIf1GxbKzHhSy8AKiAPf6VDLy1xXfw3rursUbek92oSIzViv4fPQjPHzdr7d jaUtdJqPR9E2OASW/5/NJDGSfve0eZuRloVN7orFTDRo9ZqZIjpgqoBV47kRr8XBlEF5 DBSJvbtiC8QZHXkFkGkOa/+xzlHUsCCYAMQEfdB5PEsocbn0WFnpQAJyildu0Z9iCJf6 dMcHtyWUSDyfvFf8JlKs0RIL3xmyQQMGaGgw2ge9PphTnIBJyHYGS2CYbimZOlSOFR7R w8Uw== X-Gm-Message-State: AOAM532MwIr22564AApN9joJnKtRsUPWxOKaFbNhNz+kXkMnLLdHcwGf bb8LHeKzxXqDM3m0M8Xve7qgwnBIIFuSDg== X-Google-Smtp-Source: ABdhPJxcBvIz7X+nnZAVOil6lfBgF9PLhnvtD+5MKWMfgMIX6lMCA+qxVOSaeGGfGYm7B+vKsP9Hgg== X-Received: by 2002:a05:622a:120a:b0:2e1:c9ba:e99b with SMTP id y10-20020a05622a120a00b002e1c9bae99bmr2867850qtx.685.1649165092828; Tue, 05 Apr 2022 06:24:52 -0700 (PDT) Received: from mail-yw1-f180.google.com (mail-yw1-f180.google.com. [209.85.128.180]) by smtp.gmail.com with ESMTPSA id a129-20020a376687000000b0067d186d953bsm7960042qkc.121.2022.04.05.06.24.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 05 Apr 2022 06:24:52 -0700 (PDT) Received: by mail-yw1-f180.google.com with SMTP id 00721157ae682-2eb888cf7e7so47571727b3.13; Tue, 05 Apr 2022 06:24:52 -0700 (PDT) X-Received: by 2002:a81:618b:0:b0:2db:d952:8a39 with SMTP id v133-20020a81618b000000b002dbd9528a39mr2679880ywb.132.1649165091759; Tue, 05 Apr 2022 06:24:51 -0700 (PDT) MIME-Version: 1.0 References: <20220208210824.2238981-1-daniel.vetter@ffwll.ch> <20220208210824.2238981-19-daniel.vetter@ffwll.ch> <4ae20b63-f452-fdb4-ced6-d4968a8d69f0@redhat.com> <408ffe9b-f09f-dc7e-7f5e-a93b311a06fa@redhat.com> In-Reply-To: From: Geert Uytterhoeven Date: Tue, 5 Apr 2022 15:24:40 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2 18/19] Revert "fbdev: Prevent probing generic drivers if a FB is already registered" To: Daniel Vetter Cc: Javier Martinez Canillas , Greg KH , DRI Development , Intel Graphics Development , Linux Fbdev development list , LKML , Thomas Zimmermann , Zack Rusin , Hans de Goede , Ilya Trukhanov , Daniel Vetter , Peter Jones Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Daniel, On Tue, Apr 5, 2022 at 1:48 PM Daniel Vetter wrote: > On Tue, 5 Apr 2022 at 11:52, Javier Martinez Canillas > wrote: > > On 4/5/22 11:24, Daniel Vetter wrote: > > > On Tue, 5 Apr 2022 at 11:19, Javier Martinez Canillas > > >> This is how I think that work, please let me know if you see something > > >> wrong in my logic: > > >> > > >> 1) A PCI device of OF device is registered for the GPU, this attempt to > > >> match a registered driver but no driver was registered that match yet. > > >> > > >> 2) The efifb driver is built-in, will be initialized according to the link > > >> order of the objects under drivers/video and the fbdev driver is registered. > > >> > > >> There is no platform device or PCI/OF device registered that matches. > > >> > > >> 3) The DRM driver is built-in, will be initialized according to the link > > >> order of the objects under drivers/gpu and the DRM driver is registered. > > >> > > >> This matches the device registered in (1) and the DRM driver probes. > > >> > > >> 4) The DRM driver .probe kicks out any conflicting DRM drivers and pdev > > >> before registering the DRM device. > > >> > > >> There are no conflicting drivers or platform device at this point. > > >> > > >> 5) Latter at some point the drivers/firmware/sysfb.c init function is > > >> executed, and this registers a platform device for the generic fb. > > >> > > >> This device matches the efifb driver registered in (2) and the fbdev > > >> driver probes. > > >> > > >> Since that happens *after* the DRM driver already matched, probed > > >> and registered the DRM device, that is a bug and what the reverted > > >> patch worked around. > > >> > > >> So we need to prevent (5) if (1) and (3) already happened. Having a flag > > >> set in the fbdev core somewhere when remove_conflicting_framebuffers() > > >> is called could be a solution indeed. > > >> > > >> That is, the fbdev core needs to know that a DRM driver already probed > > >> and make register_framebuffer() fail if info->flag & FBINFO_MISC_FIRMWARE > > >> > > >> I can attempt to write a patch for that. > > > > > > Ah yeah that could be an issue. I think the right fix is to replace > > > the platform dev unregister with a sysfb_unregister() function in > > > sysfb.c, which is synced with a common lock with the sysfb_init > > > function and a small boolean. I think I can type that up quickly for > > > v3. > > > > It's more complicated than that since sysfb is just *one* of the several > > places where platform devices can be registered for video devices. > > > > For instance, the vga16fb driver registers its own platform device in > > its module_init() function so that can also happen after the conflicting > > framebuffers (and associated devices) were removed by a DRM driver probe. > > > > I tried to minimize the issue for that particular driver with commit: > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0499f419b76f > > > > But the point stands, it all boils down to the fact that you have two > > different subsystems registering video drivers and they don't know all > > about each other to take a proper decision. > > > > Right now the drm_aperture_remove_conflicting_framebuffers() call signals > > in one direction from DRM to fbdev but there isn't a communication in the > > other direction, from fbdev to DRM. > > > > I believe the correct fix would be for the fbdev core to keep a list of > > the apertures struct that are passed to remove_conflicting_framebuffers(), > > that way it will know what apertures are not available anymore and prevent > > to register any fbdev framebuffer that conflicts with one already present. > > Hm that still feels like reinventing a driver model, badly. > > I think there's two cleaner solutions: > - move all the firmware driver platform_dev into sysfb.c, and then > just bind the special cases against that (e.g. offb, vga16fb and all > these). Then we'd have one sysfb_try_unregister(struct device *dev) > interface that fbmem.c uses. > - let fbmem.c call into each of these firmware device providers, which > means some loops most likely (like we can't call into vga16fb), so > probably need to move that into fbmem.c and it all gets a bit messy. > > > Let me know if you think that makes sense and I can attempt to write a fix. > > I still think unregistering the platform_dev properly makes the most That doesn't sound very driver-model-aware to me. The device is what the driver binds to; it does not cease to exist. > sense, and feels like the most proper linux device model solution > instead of hacks on top - if the firmware fb is unuseable because a > native driver has taken over, we should nuke that. And also the > firmware fb driver would then just bind to that platform_dev if it > exists, and only if it exists. Also I think it should be the > responsibility of whichever piece of code that registers these > platform devices to ensure that platform_dev actually still exists. > That's why I think pushing all that code into sysfb.c is probably the > cleanest solution. Can't you unbind the generic driver first, and bind the specific driver afterwards? Alike writing to sysfs unbind/driver_override/bind, but from code? Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds