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 70F26C433EF for ; Tue, 5 Apr 2022 10:33:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230330AbiDEKfp (ORCPT ); Tue, 5 Apr 2022 06:35:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53956 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239675AbiDEJfb (ORCPT ); Tue, 5 Apr 2022 05:35:31 -0400 Received: from mail-oa1-x34.google.com (mail-oa1-x34.google.com [IPv6:2001:4860:4864:20::34]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 26F0388B3B for ; Tue, 5 Apr 2022 02:24:13 -0700 (PDT) Received: by mail-oa1-x34.google.com with SMTP id 586e51a60fabf-ddfa38f1c1so13718906fac.11 for ; Tue, 05 Apr 2022 02:24:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=8lxRDcdRQ5w1Q2jCVMX+xvmqdaWkgW8uu97T4fHS8x4=; b=E7utYSEQMMriUu3qMfwO6HZ+45PXmrgq9OM+1s//K6zpWGIFlVpV9kYS7Tmb7YhWlD NkBhw6QH+PA6UFcYFNsQg+mT3l+j/b3yiMV0z5OgJqRnaezfoO6hggNnTdTjEqHTI0zV 2wAOmzOy1RGhDB2wL/45uzYgskBCHCu8iM08c= 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=8lxRDcdRQ5w1Q2jCVMX+xvmqdaWkgW8uu97T4fHS8x4=; b=wdtwOOYTVExtpNoDFN2GHLxWBXkFP74A3fxK92g61VQec4Hc3ha/A8WTh9g/zclx0A 5az1VZSkNTjBr0iMZ2kAzSgk01d94B/0S261OJu+cbdhgoolG8smZfW2581ePVh+pH/n ildRQ7Hu6udGyw8Nt0tAN9iXLCKlTaIINrCo3WVHOau3j4fC2HrItqhahnvR18drPh0w /C9QHGAnQ90wlg/ZQQksxUbLqRccIPDAwA/GfriIfclmwT+LOHt+d6tMb67Wmo9Sa+KQ +AUI2+C685za+p+zyXkhdiSJXrpc9zUMZlwaiBezIwW79wXKJ2e7FmVjlZlB4N7CAlWz Evag== X-Gm-Message-State: AOAM532GZZG5vuRA9Iebah78DGX8W55IKtKeSELdSMJ/ALl9t84KhfBQ Z7NXa9U0Nt9LvmJQqhl1P0OJ9G9jV9o7Ul5adixItw== X-Google-Smtp-Source: ABdhPJyzL3zZzTHLZEn2qSsiB+5Zic+Cf7QVJB23RMBqDKq8SPt6RfSyxRU86S94alZw81SeHDZ6ususLht4Jn/mafs= X-Received: by 2002:a05:6870:eaa5:b0:da:b3f:2b45 with SMTP id s37-20020a056870eaa500b000da0b3f2b45mr1132529oap.228.1649150653253; Tue, 05 Apr 2022 02:24:13 -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: <408ffe9b-f09f-dc7e-7f5e-a93b311a06fa@redhat.com> From: Daniel Vetter Date: Tue, 5 Apr 2022 11:24:01 +0200 Message-ID: Subject: Re: [PATCH v2 18/19] Revert "fbdev: Prevent probing generic drivers if a FB is already registered" To: Javier Martinez Canillas Cc: DRI Development , Intel Graphics Development , linux-fbdev@vger.kernel.org, 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-fbdev@vger.kernel.org On Tue, 5 Apr 2022 at 11:19, Javier Martinez Canillas wrote: > > Hello Daniel, > > On 4/5/22 10:40, Daniel Vetter wrote: > > On Tue, Apr 05, 2022 at 10:36:35AM +0200, Daniel Vetter wrote: > >> On Wed, Feb 09, 2022 at 01:19:26AM +0100, Javier Martinez Canillas wrote: > >>> On 2/8/22 22:08, Daniel Vetter wrote: > >>>> This reverts commit fb561bf9abde49f7e00fdbf9ed2ccf2d86cac8ee. > >>>> > >>>> With > >>>> > >>>> commit 27599aacbaefcbf2af7b06b0029459bbf682000d > >>>> Author: Thomas Zimmermann > >>>> Date: Tue Jan 25 10:12:18 2022 +0100 > >>>> > >>>> fbdev: Hot-unplug firmware fb devices on forced removal > >>>> > >>>> this should be fixed properly and we can remove this somewhat hackish > >>>> check here (e.g. this won't catch drm drivers if fbdev emulation isn't > >>>> enabled). > >>>> > >>> > >>> Unfortunately this hack can't be reverted yet. Thomas' patch solves the issue > >>> of platform devices matched with fbdev drivers to be properly unregistered if > >>> a DRM driver attempts to remove all the conflicting framebuffers. > >>> > >>> But the problem that fb561bf9abde ("fbdev: Prevent probing generic drivers if > >>> a FB is already registered") worked around is different. It happens when the > >>> DRM driver is probed before the {efi,simple}fb and other fbdev drivers, the > >>> kicking out of conflicting framebuffers already happened and these drivers > >>> will be allowed to probe even when a DRM driver is already present. > >>> > >>> We need a clearer way to prevent it, but can't revert fb561bf9abde until that. > >> > >> Yeah that entire area is a mess still, ideally we'd have something else > >> creating the platform devices, and efifb/offb and all these would just > >> bind against them. > >> > >> Hm one idea that just crossed my mind: Could we have a flag in fb_info for > >> fw drivers, and check this in framebuffer_register? Then at least all the > >> logic would be in the fbdev core. > > > > I can't answer right away since I've since forgotten this part of the code > and will require to do a detailed read to refresh my memory. > > I'll answer later but preferred to mention the other question ASAP. > > > Ok coffee just kicked in, how exactly does your scenario work? > > > > This code I'm reverting here is in the platform_dev->probe function. > > Thomas' patch removes the platform_dev. How exactly can you still probe > > against a platform dev if that platform dev is gone? > > > > Because the platform was not even registered by the time the DRM driver > probed and all the devices for the conflicting drivers were unregistered. > > > Iow, now that I reponder your case after a few weeks I'm no longer sure > > things work like you claim. > > > > 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. -Daniel > > -- > Best regards, > > Javier Martinez Canillas > Linux Engineering > Red Hat > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch