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bh=1qVWteth2CW4grxymKBfkcAQ2Y6lgyq+8fjlcjGvCdE=; b=pWGSpGSfBZkjXtE6lj76qjxTTU7v28kiwiq9wRoAZ3aAPRRV+Fhr40paxglFA656gZ53M4 1DSAyAx8WxL2H+AQ== 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 4CE7F3EA63; Tue, 25 Nov 2025 16:22:07 +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 hQZWEa/XJWm8VQAAD6G6ig (envelope-from ); Tue, 25 Nov 2025 16:22:07 +0000 Message-ID: <65622142-c3b0-4ef3-9a74-09420bc2220d@suse.de> Date: Tue, 25 Nov 2025 17:22:06 +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: 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, danielt@kernel.org, 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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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: CE0FC2279F X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spamd-Result: default: False [-4.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; RCPT_COUNT_TWELVE(0.00)[19]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; MIME_TRACE(0.00)[0:+]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCVD_TLS_ALL(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com,gmx.de]; MID_RHS_MATCH_FROM(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[ffwll.ch,gmail.com,amd.com,redhat.com,kernel.org,gmx.de,linux.intel.com,windriver.com,lists.freedesktop.org,vger.kernel.org,lichtman.org]; TO_DN_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns,suse.com:url,suse.de:email,suse.de:mid,suse.de:dkim]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DKIM_TRACE(0.00)[suse.de:+] X-Rspamd-Action: no action X-Spam-Flag: NO X-Spam-Score: -4.51 X-Spam-Level: Hi Am 25.11.25 um 16:26 schrieb Doug Anderson: > Hi, > > On Tue, Nov 25, 2025 at 5:06 AM Thomas Zimmermann wrote: >> Remove the rest of the kbd support from DRM. Driver support has been >> broken for years without anyone complaining. >> >> Kdb cannot use regular DRM mode setting, so DRM drivers have to >> implement an additional hook to make it work (in theory). As outlined >> by Sima in commit 9c79e0b1d096 ("drm/fb-helper: Give up on kgdb for >> atomic drivers") from 2017, kdb is not compatible with DRM atomic mode >> setting. Non-atomic mode setting meanwhile has become rare. >> >> Only 3 DRM drivers implement the hooks for kdb support. Amdgpu and >> nouveau use non-atomic mode setting on older devices. But both drivers >> have switched to generic fbdev emulation, which isn't compatible with >> kdb. Radeon still runs kdb, but it doesn't work in practice. See the >> commits in this series for details >> >> 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 I wonder which driver or kernel that person was using. None of the current drivers would be working. Best regards Thomas > > Daniel may also have comments here? > > -Doug > -- -- 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)