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Fri, 30 Oct 2026 08:48:20 +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 CcebGNRZ5GoCMwAAD6G6ig (envelope-from ); Fri, 30 Oct 2026 08:48:20 +0000 Message-ID: <4379fd92-ac4f-45c2-9f4a-eaabe4b7f981@suse.de> Date: Fri, 30 Oct 2026 09:48:19 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] x86/video: Preserve the default VGA fallback for legacy modes To: Hengyu Liang , x86@kernel.org Cc: mario.limonciello@amd.com, aaron.ma@canonical.com, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, dri-devel@lists.freedesktop.org References: <20261029162311.3389523-1-hengyul@cs.unc.edu> Content-Language: en-US From: Thomas Zimmermann Autocrypt: addr=tzimmermann@suse.de; keydata= xsBNBFs50uABCADEHPidWt974CaxBVbrIBwqcq/WURinJ3+2WlIrKWspiP83vfZKaXhFYsdg XH47fDVbPPj+d6tQrw5lPQCyqjwrCPYnq3WlIBnGPJ4/jreTL6V+qfKRDlGLWFjZcsrPJGE0 BeB5BbqP5erN1qylK9i3gPoQjXGhpBpQYwRrEyQyjuvk+Ev0K1Jc5tVDeJAuau3TGNgah4Yc hdHm3bkPjz9EErV85RwvImQ1dptvx6s7xzwXTgGAsaYZsL8WCwDaTuqFa1d1jjlaxg6+tZsB 9GluwvIhSezPgnEmimZDkGnZRRSFiGP8yjqTjjWuf0bSj5rUnTGiyLyRZRNGcXmu6hjlABEB AAHNJ1Rob21hcyBaaW1tZXJtYW5uIDx0emltbWVybWFubkBzdXNlLmRlPsLAjgQTAQgAOAIb AwULCQgHAgYVCgkICwIEFgIDAQIeAQIXgBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftODH AAoJEGgNwR1TC3ojx1wH/0hKGWugiqDgLNXLRD/4TfHBEKmxIrmfu9Z5t7vwUKfwhFL6hqvo lXPJJKQpQ2z8+X2vZm/slsLn7J1yjrOsoJhKABDi+3QWWSGkaGwRJAdPVVyJMfJRNNNIKwVb U6B1BkX2XDKDGffF4TxlOpSQzdtNI/9gleOoUA8+jy8knnDYzjBNOZqLG2FuTdicBXblz0Mf vg41gd9kCwYXDnD91rJU8tzylXv03E75NCaTxTM+FBXPmsAVYQ4GYhhgFt8S2UWMoaaABLDe 7l5FdnLdDEcbmd8uLU2CaG4W2cLrUaI4jz2XbkcPQkqTQ3EB67hYkjiEE6Zy3ggOitiQGcqp j//OwE0EWznS4AEIAMYmP4M/V+T5RY5at/g7rUdNsLhWv1APYrh9RQefODYHrNRHUE9eosYb T6XMryR9hT8XlGOYRwKWwiQBoWSDiTMo/Xi29jUnn4BXfI2px2DTXwc22LKtLAgTRjP+qbU6 3Y0xnQN29UGDbYgyyK51DW3H0If2a3JNsheAAK+Xc9baj0LGIc8T9uiEWHBnCH+RdhgATnWW GKdDegUR5BkDfDg5O/FISymJBHx2Dyoklv5g4BzkgqTqwmaYzsl8UxZKvbaxq0zbehDda8lv hFXodNFMAgTLJlLuDYOGLK2AwbrS3Sp0AEbkpdJBb44qVlGm5bApZouHeJ/+n+7r12+lqdsA EQEAAcLAdgQYAQgAIAIbDBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftOH6AAoJEGgNwR1T C3ojVSkIALpAPkIJPQoURPb1VWjh34l0HlglmYHvZszJWTXYwavHR8+k6Baa6H7ufXNQtThR yIxJrQLW6rV5lm7TjhffEhxVCn37+cg0zZ3j7zIsSS0rx/aMwi6VhFJA5hfn3T0TtrijKP4A SAQO9xD1Zk9/61JWk8OysuIh7MXkl0fxbRKWE93XeQBhIJHQfnc+YBLprdnxR446Sh8Wn/2D Ya8cavuWf2zrB6cZurs048xe0UbSW5AOSo4V9M0jzYI4nZqTmPxYyXbm30Kvmz0rYVRaitYJ 4kyYYMhuULvrJDMjZRvaNe52tkKAvMevcGdt38H4KSVXAylqyQOW5zvPc4/sq9c= In-Reply-To: <20261029162311.3389523-1-hengyul@cs.unc.edu> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Spam-Flag: NO X-Spam-Level: X-Spamd-Result: default: False [-13.29 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; BAYES_HAM(-3.00)[100.00%]; NEURAL_HAM_LONG(-1.00)[-0.998]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; XM_UA_NO_VERSION(0.01)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; RCVD_TLS_ALL(0.00)[]; FROM_HAS_DN(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; RCPT_COUNT_SEVEN(0.00)[7]; MID_RHS_MATCH_FROM(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.com:url,unc.edu:email,bootlin.com:url,imap1.dmz-prg2.suse.org:helo] X-Spam-Score: -13.29 Hi Am 29.10.26 um 17:23 schrieb Hengyu Liang: > Commit 596b3678326d ("x86/video: Only fall back to vga_default_device() > without screen info") made video_is_primary_device() rely exclusively > on screen_info resources whenever any are available. > > However, screen_info_resources() also returns legacy I/O and memory > ranges for VGA text modes. These ranges are not PCI BARs, so the resource > lookup fails and the default VGA fallback is skipped. If the BIOS booted in text mode or VGA graphics mode, the rsp device is still the primary display device. So the current matching code is not necessarily incorrect. (But also not necessarily correct either. :) > > On a SeaBIOS QEMU guest with bochs and VKMS, the boot VGA loses its DRM > boot_display attribute and fbcon leaves the console on VKMS. This can > be checked with: > > cat /sys/class/drm/card1/boot_display > stty -F /dev/tty1 size > > Without the fix, boot_display is missing and tty1 is 48 rows by 128 > columns. With it, boot_display contains 1 and tty1 is 50 rows by 160 > columns. > > Use resource-based selection only for linear framebuffers. Fall back to > vga_default_device() for legacy display modes, while keeping EFI and > VESA framebuffer ownership authoritative. > > Fixes: 596b3678326d ("x86/video: Only fall back to vga_default_device() without screen info") > Cc: stable@vger.kernel.org > Signed-off-by: Hengyu Liang > --- > Tested in QEMU/KVM with identical KASAN configs: SeaBIOS VGA text mode > (with and without VKMS), VESA, and OVMF with one and two virtual GPUs. > All 26 guest-only helper checks pass, including EFI/VESA framebuffer > ownership, missing framebuffer resources, and addresses above 4 GiB. > Also build-tested x86-32 with/without CONFIG_SCREEN_INFO, and x86-64 > without CONFIG_SCREEN_INFO. > > arch/x86/video/video-common.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/video/video-common.c b/arch/x86/video/video-common.c > index 8ed82fff7638..b8f83346dfe8 100644 > --- a/arch/x86/video/video-common.c > +++ b/arch/x86/video/video-common.c > @@ -45,7 +45,7 @@ bool video_is_primary_device(struct device *dev) > > #ifdef CONFIG_SCREEN_INFO > numres = screen_info_resources(si, res, ARRAY_SIZE(res)); > - if (numres > 0) { > + if (numres > 0 && __screen_info_has_lfb(screen_info_video_type(si))) { > for (i = 0; i < numres; ++i) { > if (!(res[i].flags & IORESOURCE_MEM)) > continue; Further below in that code is a call to pci_find_resource(). [1]  Why does it match with vkms?  Vkms is not even on a PCI device. [1] https://elixir.bootlin.com/linux/v7.3/source/arch/x86/video/video-common.c#L53 Best regards Thomas > > base-commit: c339f4010dea8b0d754f84ace70cd1b089878ef8 -- -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com GF: Stefan Gaiser, Jochen Jaser, Abhinav Puri, (HRB 36809, AG Nürnberg)