From patchwork Fri Nov 23 09:24:55 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Paul Kocialkowski X-Patchwork-Id: 10695321 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 0F10C175A for ; Fri, 23 Nov 2018 09:27:23 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id F2B522C3D8 for ; Fri, 23 Nov 2018 09:27:22 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id E705B2C419; Fri, 23 Nov 2018 09:27:22 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 771362C3D8 for ; Fri, 23 Nov 2018 09:27:22 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 4DF416E620; Fri, 23 Nov 2018 09:27:08 +0000 (UTC) X-Original-To: dri-devel@lists.freedesktop.org Delivered-To: dri-devel@lists.freedesktop.org Received: from mail.bootlin.com (mail.bootlin.com [62.4.15.54]) by gabe.freedesktop.org (Postfix) with ESMTP id 837A86E618 for ; Fri, 23 Nov 2018 09:26:59 +0000 (UTC) Received: by mail.bootlin.com (Postfix, from userid 110) id 5D23820DF0; Fri, 23 Nov 2018 10:26:58 +0100 (CET) Received: from localhost.localdomain (aaubervilliers-681-1-94-205.w90-88.abo.wanadoo.fr [90.88.35.205]) by mail.bootlin.com (Postfix) with ESMTPSA id 7659720DF9; Fri, 23 Nov 2018 10:26:33 +0100 (CET) From: Paul Kocialkowski To: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-arm-kernel@lists.infradead.org Subject: [PATCH v2 23/43] drm/sun4i: backend: Detail the YUV to RGB values coding explanation Date: Fri, 23 Nov 2018 10:24:55 +0100 Message-Id: <20181123092515.2511-24-paul.kocialkowski@bootlin.com> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20181123092515.2511-1-paul.kocialkowski@bootlin.com> References: <20181123092515.2511-1-paul.kocialkowski@bootlin.com> MIME-Version: 1.0 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Maxime Ripard , linux-sunxi@googlegroups.com, Paul Kocialkowski , David Airlie , Chen-Yu Tsai , Thomas Petazzoni , Sean Paul Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" X-Virus-Scanned: ClamAV using ClamSMTP From: Paul Kocialkowski The values in the BT601 YUV to RGB colorspace translation are not simply coded as multiples, but rather as fixed-point signed fractional values on a given number of bits. Add an explanation about that. Signed-off-by: Paul Kocialkowski --- drivers/gpu/drm/sun4i/sun4i_backend.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/sun4i/sun4i_backend.c b/drivers/gpu/drm/sun4i/sun4i_backend.c index a39d8b75d76a..986bdb64521c 100644 --- a/drivers/gpu/drm/sun4i/sun4i_backend.c +++ b/drivers/gpu/drm/sun4i/sun4i_backend.c @@ -48,8 +48,12 @@ static const u32 sunxi_rgb2yuv_coef[12] = { /* * These coefficients are taken from the A33 BSP from Allwinner. * - * The formula is for each component, each coefficient being multiplied by - * 1024 and each constant being multiplied by 16: + * The first three values of each row are coded as 13-bit signed fixed-point + * numbers, with 10 bits for the fractional part. The fourth value is a + * constant coded as a 14-bit signed fixed-point number with 4 bits for the + * fractional part. + * + * The values in table order give the following colorspace translation: * G = 1.164 * Y - 0.391 * U - 0.813 * V + 135 * R = 1.164 * Y + 1.596 * V - 222 * B = 1.164 * Y + 2.018 * U + 276