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bh=hIZg0NrBErhJe7J0VcGIQwXQFyhWuMVsY6KJ1KKoZJo=; b=4/+ETEnEFvDi03gyIpr9+BPhTRn6YhY4FV7tF5EoKo1NfmkTHZV4kyteispDmmTSb83Lyx +5NndoTVIifx+uAg== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 6F4B53EA63; Wed, 26 Nov 2025 13:32:33 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id +a+/GXEBJ2lZBwAAD6G6ig (envelope-from ); Wed, 26 Nov 2025 13:32:33 +0000 Message-ID: <054f60ca-b898-488f-81f4-14eed0a1360b@suse.de> Date: Wed, 26 Nov 2025 14:32:32 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/5] drm: Remove remaining support for kdb To: Daniel Thompson , Doug Anderson Cc: simona@ffwll.ch, airlied@gmail.com, alexander.deucher@amd.com, christian.koenig@amd.com, lyude@redhat.com, dakr@kernel.org, deller@gmx.de, mripard@kernel.org, maarten.lankhorst@linux.intel.com, jason.wessel@windriver.com, dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, nouveau@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Nir Lichtman References: <20251125130634.1080966-1-tzimmermann@suse.de> Content-Language: en-US From: Thomas Zimmermann Autocrypt: addr=tzimmermann@suse.de; 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DKIM_TRACE(0.00)[suse.de:+] X-Rspamd-Action: no action X-Spam-Flag: NO X-Spam-Score: -3.51 X-Spam-Level: X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-Rspamd-Queue-Id: ED5A233689 Hi Am 26.11.25 um 13:19 schrieb Daniel Thompson: > On Tue, Nov 25, 2025 at 07:26:33AM -0800, Doug Anderson wrote: >> On Tue, Nov 25, 2025 at 5:06 AM Thomas Zimmermann wrote: >>> >>> Therefore remove the remaining support for kdb from the DRM drivers >>> and from DRM fbdev emulation. Also remove the hooks from fbdev, as >>> there are no fbdev drivers with kdb support. >>> >>> If we ever want to address kdb support within DRM drivers, a place to >>> start would be the scanout buffers used by DRM's panic screen. These >>> use the current display mode. They can be written and flushed without >>> mode setting involved. >>> >>> Note: kdb over serial lines is not affected by this series and continues >>> to work as before. >>> >>> Thomas Zimmermann (5): >>> drm/amdgpu: Do not implement mode_set_base_atomic callback >>> drm/nouveau: Do not implement mode_set_base_atomic callback >>> drm/radeon: Do not implement mode_set_base_atomic callback >>> drm/fbdev-helper: Remove drm_fb_helper_debug_enter/_leave() >>> fbcon: Remove fb_debug_enter/_leave from struct fb_ops >> Personally, I've never worked with kdb over anything other than >> serial, so this won't bother any of my normal workflows. That being >> said, at least as of a year ago someone on the lists was talking about >> using kdb with a keyboard and (presumably) a display. You can see a >> thread here: >> >> http://lore.kernel.org/r/20241031192350.GA26688@lichtman.org >> >> Daniel may also have comments here? > TL;DR - I'm pretty relaxed about these changes... but I'd like > to know how to test the changes. > > Like Doug I only really use kdb via serial but, since I'm maintain > the thing I do occasionally test kdb works on the qemu console. I don't > do it very often though because it's a manual test! > > I'd assume that will still work since it won't involve any of the > drivers above. I'm afraid I can't double check that since patch 4 > doesn't apply cleanly in v6.18-rc7 (nor to linux-next... and neither > does the base-commit appear in linux-next). To test its effects, ignore this series and simply clear the two calbacks at [1]. This is where the debugger invokes fbcon. The series removes their implementation in the final patch. [1] https://elixir.bootlin.com/linux/v6.17.9/source/drivers/video/fbdev/core/fbcon.c#L3202 Best regards Thomas > > Anyhow, the only testing I do for kgdboc=kms,kdb is to boot an x86-64 > defconfig+kgdb+kdb kernel in qemu with something like the following > command line, which FWIW does still work: > > qemu-system-x86_64 -enable-kvm -m 1G -smp 2 \ > -kernel arch/x86/boot/bzImage \ > -monitor none -chardev stdio,id=mon,mux=on,signal=off \ > -serial chardev:mon \ > -initrd rootfs.cpio.gz \ > -append " console=tty0 console=ttyS0,115200 kgdboc=kms,kbd,ttyS0 kgdbwait" > > The reason I'm fairly relaxed about changes here is that the kbd driver > only works on PCs with legacy keyboard interfaces. If the kernel is > talking to the keyboard using USB or I2C (which almost all PCs do) then > kdb cannot be used anyway. > > So... it would be a "cool project"[1] to get kdb running on > a special interrupt-free I2C mode and with the DRM panic code so you > can do live analysis if your laptop/chomebook crashes. However it is > simply not "real enough" to justify slowing down other developers. > > > Daniel. > > > [1] ... but not quite cool enough that I see myself spending time on it > though! > -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)