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 09FA5CD8C9F for ; Mon, 8 Jun 2026 11:46:36 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 6732E10F259; Mon, 8 Jun 2026 11:46:35 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (1024-bit key; unprotected) header.d=collabora.com header.i=nicolas.frattaroli@collabora.com header.b="Cl82lHQk"; dkim-atps=neutral Received: from sender4-pp-f112.zoho.com (sender4-pp-f112.zoho.com [136.143.188.112]) by gabe.freedesktop.org (Postfix) with ESMTPS id 9C73510F259 for ; Mon, 8 Jun 2026 11:46:34 +0000 (UTC) ARC-Seal: i=1; a=rsa-sha256; t=1780919192; cv=none; d=zohomail.com; s=zohoarc; b=IZnK2esWM0HeOWRj3yx5gkyStBBtajBWiqmaUsCjO52urHadfjRXH0YqXZ4WNnXUQ9OV8juCa3JLu6EhC1hwK7sjfRiYyxVKbNcDLOWBvvvAntjx2a1vMEYHUJVPKyjZkkINklMpJKRnd05vbKSO0aLW8o3giROdKevaFw2/3I4= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1780919192; h=Content-Type:Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:In-Reply-To:MIME-Version:Message-ID:References:Subject:Subject:To:To:Message-Id:Reply-To; bh=Gpm9tofYuThT3DdGwbZoDTaTeH3rNfgAGSRNVApSjTA=; b=MjLMHJMJsiX3qU8m/0Hea+0zzwe7Tun5Wucb6WaG9sOnvcMkr8RCO3he/BKwNMLAZBb7m1JoVSzWQDpFn/boy4KO4xuwVokXVaY7KeiXOr5IL6OJi41aAke1gqRTW/xP+XoXkekHDGCew9Fm44oboBOo+T7Jp/2/efL6gY8fekM= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass header.i=collabora.com; spf=pass smtp.mailfrom=nicolas.frattaroli@collabora.com; dmarc=pass header.from= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1780919192; s=zohomail; d=collabora.com; i=nicolas.frattaroli@collabora.com; h=From:From:To:To:Cc:Cc:Subject:Subject:Date:Date:Message-ID:In-Reply-To:References:MIME-Version:Content-Transfer-Encoding:Content-Type:Message-Id:Reply-To; bh=Gpm9tofYuThT3DdGwbZoDTaTeH3rNfgAGSRNVApSjTA=; b=Cl82lHQk7yZPYok+4QE6Mte20DyBADBoLssm/B+KOJH+STu91OCSkc/s1lyB7D/N GUQ+UPmgspfbzQTonfskiaEFKJiPj/f7jSQa6FcTXv/t+DLLmYpv0fiCp+BJTRvrvkS pHLiMtRJL7ahRcpgooRxtlveXBA3KSEGF8esCsaQ= Received: by mx.zohomail.com with SMTPS id 178091919124684.90521949997265; Mon, 8 Jun 2026 04:46:31 -0700 (PDT) From: Nicolas Frattaroli To: sashiko-reviews@lists.linux.dev Cc: dri-devel@lists.freedesktop.org Subject: Re: [PATCH 1/2] drm/display: hdmi: Only allow BPC values of 8, 10, 12 and 16 Date: Mon, 08 Jun 2026 13:46:27 +0200 Message-ID: In-Reply-To: <20260608113023.67AFB1F00893@smtp.kernel.org> References: <20260608-hdmi-max-bpc-fix-v1-1-6e8dcebc7274@collabora.com> <20260608113023.67AFB1F00893@smtp.kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" 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 Monday, 8 June 2026 13:30:22 Central European Summer Time sashiko-bot@kernel.org wrote: > Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: > > Pre-existing issues: > - [High] The function `sink_supports_format_bpc` explicitly permits 16 BPC for RGB444 and YCBCR444 formats without verifying if the sink's EDID actually supports 48-bit deep color. > -- > > commit 767fa3cc832e8b93f697ad91bcc66e5b3b1ed85d > Author: Nicolas Frattaroli > > drm/display: hdmi: Only allow BPC values of 8, 10, 12 and 16 > > As per the comment in sink_supports_format_bpc(), CTA-861-F defines that > only bits-per-channel values of 8, 10, 12 and 16 are allowed for HDMI. > Allowing more than this has surprising consequences for the atomic check > phase. > > > diff --git a/drivers/gpu/drm/display/drm_hdmi_state_helper.c b/drivers/gpu/drm/display/drm_hdmi_state_helper.c > > index 4867edbf2622b..b06499dbfe8b3 100644 > > --- a/drivers/gpu/drm/display/drm_hdmi_state_helper.c > > +++ b/drivers/gpu/drm/display/drm_hdmi_state_helper.c > > @@ -419,6 +419,16 @@ sink_supports_format_bpc(const struct drm_connector *connector, > > return false; > > } > > > > + switch (bpc) { > > + case 8: > > + case 10: > > + case 12: > > + case 16: > > [Severity: High] > This is a pre-existing issue, but does explicitly allowing 16 BPC here > expose a missing validation check for 48-bit deep color further down in > sink_supports_format_bpc()? > > When checking DRM_OUTPUT_COLOR_FORMAT_RGB444 and > DRM_OUTPUT_COLOR_FORMAT_YCBCR444, the code validates 10 BPC and 12 BPC > against the EDID flags, but completely omits checking 16 BPC against > DRM_EDID_HDMI_DC_48: > > drivers/gpu/drm/display/drm_hdmi_state_helper.c:sink_supports_format_bpc() { > ... > case DRM_OUTPUT_COLOR_FORMAT_RGB444: > ... > if (bpc == 10 && !(info->edid_hdmi_rgb444_dc_modes & DRM_EDID_HDMI_DC_30)) { > drm_dbg_kms(dev, "10 BPC but sink doesn't support Deep Color 30.\n"); > return false; > } > > if (bpc == 12 && !(info->edid_hdmi_rgb444_dc_modes & DRM_EDID_HDMI_DC_36)) { > drm_dbg_kms(dev, "12 BPC but sink doesn't support Deep Color 36.\n"); > return false; > } > > drm_dbg_kms(dev, "RGB format supported in that configuration.\n"); > return true; > ... > } > > If the TMDS clock limit permits it, the driver might incorrectly conclude > that the sink supports 16 BPC and program the hardware accordingly, which > could result in a black screen if the monitor doesn't actually support > 48-bit deep color. > > Should a check for (info->edid_hdmi_rgb444_dc_modes & DRM_EDID_HDMI_DC_48) > be added for the RGB444 and YCBCR444 cases? Finally, we have automated the ultimate Linux kernel review response: "while you're at it, can you fix everything else wrong in this code?" (No, this does not expose any pre-existing issue; the validation is more restrictive than it was before. That it's still not restrictive enough in all cases does not introduce a new problem.) > > > + break; > > + default: > > + return false; > > + } > > + > > if (!info->is_hdmi && > > (format != DRM_OUTPUT_COLOR_FORMAT_RGB444 || bpc != 8)) { > > drm_dbg_kms(dev, "DVI Monitors require an RGB output at 8 bpc\n"); > >