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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 68D71F46456 for ; Mon, 16 Mar 2026 11:38:32 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 9E4AE10E324; Mon, 16 Mar 2026 11:38:31 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.b="V5A/IBan"; dkim-atps=neutral Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.17]) by gabe.freedesktop.org (Postfix) with ESMTPS id 071CC10E261 for ; Mon, 16 Mar 2026 11:38:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1773661110; x=1805197110; h=from:to:cc:subject:in-reply-to:references:date: message-id:mime-version:content-transfer-encoding; bh=+R6gKdN94J8gAlUgGk+V1A9HkdVF8gpG1K0Cax4/Y0w=; b=V5A/IBaniUaTIAIrPjtmRbSjB71wEQT2oFvsyzLuk5e3gXI6HA1TXw4m Se0wAA9LoHEGfB8q0Hd4SP6qAIzxyX6Ra/N2oNjSxVCwUA1Lh+1XGGRf8 QfIYX48c8NkXu78SVlTC48u/0kD8udL6OZ+mNpqP8GGDVLut5fikAPMKB 2ZN+zFMcIjFVuZTMfBBfIuvBY8FFYPn1mRToVKZLjyKbM/gZS1vqMfzA2 zpHIpenUfX1tLr6HbDhUXA5WdoDl+gtR7H3u7AlBAjnK/QEdbNM289wIm lHugQ6qDEdWdx8Wh16Sz9+2VRxtoZb6pAila8tBMtv7w3QKP4zLdBwb9X w==; X-CSE-ConnectionGUID: CE8lcSPqScy0v1hCrNiPjg== X-CSE-MsgGUID: RGJ7ecacTKaJ0kknaWO8wA== X-IronPort-AV: E=McAfee;i="6800,10657,11730"; a="74591258" X-IronPort-AV: E=Sophos;i="6.23,124,1770624000"; d="scan'208";a="74591258" Received: from fmviesa006.fm.intel.com ([10.60.135.146]) by fmvoesa111.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Mar 2026 04:38:29 -0700 X-CSE-ConnectionGUID: B5rwkWNARhqGLnnb8/lkgw== X-CSE-MsgGUID: Dd2TWJwGR1WJ+oRLVEh7mw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.23,124,1770624000"; d="scan'208";a="217728754" Received: from mjarzebo-mobl1.ger.corp.intel.com (HELO localhost) ([10.245.246.238]) by fmviesa006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Mar 2026 04:38:25 -0700 From: Jani Nikula To: Thomas Zimmermann , Jammy Huang , Dave Airlie , Jocelyn Falempe , Maarten Lankhorst , Maxime Ripard , David Airlie , Simona Vetter Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] drm/ast: DisplayPort edid supports 256 bytes In-Reply-To: Organization: Intel Finland Oy - BIC 0357606-4 - c/o Alberga Business Park, 6 krs Bertel Jungin Aukio 5, 02600 Espoo, Finland References: <20260313-upstream_ast_dp_edid-v1-1-2a75b7c091b2@aspeedtech.com> Date: Mon, 16 Mar 2026 13:38:22 +0200 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Mon, 16 Mar 2026, Thomas Zimmermann wrote: > Hi Jammy > > Am 13.03.26 um 11:04 schrieb Jammy Huang: >> DisplayPort supports edid at most 256 bytes. Thus, allow it to fetch >> edid block 0 and 1. >> >> Signed-off-by: Jammy Huang >> --- >> ASPEED DisplayPort's EDID size can be 256 bytes at most. Thus, EDID >> blocks fetched can be 0 and 1. >> --- >> drivers/gpu/drm/ast/ast_dp.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/gpu/drm/ast/ast_dp.c b/drivers/gpu/drm/ast/ast_dp.c >> index 9d07dad358c..c938e1d6b1d 100644 >> --- a/drivers/gpu/drm/ast/ast_dp.c >> +++ b/drivers/gpu/drm/ast/ast_dp.c >> @@ -88,7 +88,7 @@ static int ast_astdp_read_edid_block(void *data, u8 *b= uf, unsigned int block, si >> int ret =3D 0; >> unsigned int i; >>=20=20=20 >> - if (block > 0) >> + if (block > 1) >> return -EIO; /* extension headers not supported */ > > But see the code at [1]. It clears the number of extensions to zero and=20 > updates the checksum accordingly. This is required to make the shortened= =20 > EDID work with DRM. If you leave this as-is, it will still clear support= =20 > for any extension in block 1. > > See the table 2.4 in the VESA EDID 1.4 standard for the semantics. For=20 > 1.3, if the number of blocks is >2, the first extensions is a 'block map= =20 > of the extensions'. This is useless, as it's not a data extension in=20 > itself.=C2=A0 In 1.4, the block map is optional. That code should clear t= he=20 > EDID's number of extensions to 0 or 1, depending on whether there is a=20 > block map to be expected. I think long-term the goal should be for the kernel to not modify the EDID, at all. BR, Jani. > > Best regards > Thomas > > [1]=20 > https://elixir.bootlin.com/linux/v6.19.8/source/drivers/gpu/drm/ast/ast_d= p.c#L157 > >>=20=20=20 >> /* >> >> --- >> base-commit: 5ee8dbf54602dc340d6235b1d6aa17c0f283f48c >> change-id: 20260313-upstream_ast_dp_edid-5fe6adf7ad36 >> >> Best regards, --=20 Jani Nikula, Intel