From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0FD13431E76 for ; Thu, 27 Aug 2026 19:12:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787857979; cv=none; b=BYjLlgoGDLjU+/N603oPSZKGxjH8F5Zyd/VJGVg3uIN/jbiEfkV2UCDRQXCDyY23pVrGxvVQ0v1vBhCPHhQkHH1Gh6iJjtuGMP1h1QiWefT0VXbqAix4M/xy9dF2N7CaKmQ/bdWFEyj8r4X71uV2xFFbWpz27pnZftXnaxt+gPs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787857979; c=relaxed/simple; bh=UMiQ6H0crQ6QlfgYbkqDfbG+2kNs5ob1b4gkM54mkHs=; h=From:Subject:To:Cc:In-Reply-To:References:Content-Type:Date: Message-Id; b=O8R28NNohRD9EXyRuuOAN1Ucls8ocTEsqV/3v3B9PQMGg23s7FFcJ2t+K5iUqnPhDmbL3NKUP2jUi9+L+xxfjTGX9h3XKu1JrD/2qnDHYYFpi++bcIIfY7zkAKib9sFXzRCCgjjcAhzjzovmtkAEhLvBVdsNrucFF7uHcTJGa44= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SYlQ6J1j; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="SYlQ6J1j" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AE0A51F000E9; Thu, 27 Aug 2026 19:12:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787857977; bh=n/prNACSm7ZD+vf9e96Ht6fX4eX3xVkiLOEXo1W+KBA=; h=From:Subject:Reply-To:To:Cc:In-Reply-To:References:Date; b=SYlQ6J1j0JuUZur+PsSqfbunc9x4lITrP7q3r/JSauPA8IfMm3Eswn55v2lEF4frI tPYIvbvgIFBnExt1xkfYIs/GGtWPbpjzUQWTG6QRxMjoi2YGE21Bvz7CrLbX5L/cHt lE/IJ7jMBEChlxxr3/jceWvdBH1kL8yqoCFXDCXGozXk0g8k81PmutWnUphKnpTvUI WK0GndRElaHtb2FFxwvTFlUDO3cduB46IvOQ/TbZhfh7ihr3UcpNBcshogO1fV2lWc pKHza8rYqd1y4kA84X6vk2H6Q9aHFMLfN8ZtPAHqTJgqc9qcZSq5Qn/49aFwZiueS6 8HFZ+M0iWQR9w== From: sashiko-bot@kernel.org Subject: Re: [Patch 5/9]: vt: Amend three Kconfig files Reply-To: sashiko-reviews@lists.linux.dev To: "Alan Mackenzie" Cc: linux-serial@vger.kernel.org, dri-devel@lists.freedesktop.org In-Reply-To: References: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Thu, 27 Aug 2026 19:12:57 +0000 Message-Id: <20260827191257.AE0A51F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Thank you for your contribution! Sashiko AI review found 2 potential issue(= s) to consider: - [High] Enabling CONFIG_FB_GLYPH_21BIT changes GLYPH_SZ to 4 globally, bre= aking hardware console drivers (like vgacon) and rotated fbcon drivers that= still hardcode 16-bit screen buffer accesses. - [Medium] FB_GLYPH_21BIT is a generic VT/fbdev feature but is inappropriat= ely placed in the DRM clients menu, unnecessarily restricting its use. -- commit 7b9fb605add2fa8c6f62e8ba79cee762cbcbd24c Author: Alan Mackenzie vt: Amend three Kconfig files Until it becomes clear how to integrate CONFIG_A11Y_BRAILLE_CONSOLE and CONFIG_SPEAKUP, they will remain disabled when CONFIG_FB_GLYPH_21BIT is #defined. [ ... ] > diff --git a/drivers/gpu/drm/clients/Kconfig b/drivers/gpu/drm/clients/Kc= onfig > index 6096c623d9d5b..0ce8c1506eaad 100644 > --- a/drivers/gpu/drm/clients/Kconfig > +++ b/drivers/gpu/drm/clients/Kconfig > @@ -42,6 +42,15 @@ config DRM_FBDEV_EMULATION > =20 > If in doubt, say "Y". > =20 > +config FB_GLYPH_21BIT > + bool "Enable 21-bit glyphs in the frame buffer device" > + depends on (DRM_FBDEV_EMULATION =3D y) [Severity: Medium] Could placing this generic VT/fbdev feature in the DRM clients menu inappropriately restrict its use? Native framebuffer drivers (e.g., vesafb, efifb, simplefb) might be prevent= ed from utilizing 21-bit glyph support, as this strictly requires DRM_FBDEV_EMULATION. The feature modifies the generic Virtual Terminal and fbcon subsystems, which are independent of DRM. [Severity: High] Can enabling CONFIG_FB_GLYPH_21BIT corrupt the screen buffer for hardware console drivers and rotated fbcon drivers? When this is enabled, GLYPH_SZ becomes 4 globally and VT uses 32-bit screen buffer entries. However, the consw interface still passes pointers typed as const unsigned short *, and some drivers still hardcode 16-bit accesses. For example, rotated fbcon implementations iterate the buffer using scr_rea= dw() which advances the u16 pointer by 2 bytes instead of 4, reading half-charac= ters: drivers/video/fbdev/core/fbcon_cw.c:cw_putcs_aligned() { ... src =3D par->rotated.buf + (scr_readw(s++) & charmask) * cellsize; ... } Similarly, vgacon maps physical VGA VRAM assuming exactly 16 bits per chara= cter, meaning 32-bit writes from scr_writeg in vt.c will overwrite adjacent cells in hardware memory: drivers/video/console/vgacon.c:vgacon_invert_region() { ... u16 a =3D scr_readw(p); ... scr_writew(a, p++); ... } > + help > + This option enables 21-bit glyphs in the fbdev framebuffer, > + surmounting the traditional restriction to 256/512 glyphs dating back > + to the VGA hardware of the 1980s and 1990s. To use this effectively > + you will need a suitable font and possibly a suitable keyboard layout. > + --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/apCEDM2sWv_M354-@MA= C.fritz.box?part=3D5