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 5F710108E1F7 for ; Thu, 19 Mar 2026 11:54:13 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id CA09F10E9AB; Thu, 19 Mar 2026 11:54:12 +0000 (UTC) X-Greylist: delayed 505 seconds by postgrey-1.36 at gabe; Thu, 19 Mar 2026 11:54:11 UTC Received: from ni.piap.pl (ni.piap.pl [195.187.100.5]) by gabe.freedesktop.org (Postfix) with ESMTPS id 2A3B410E9AB for ; Thu, 19 Mar 2026 11:54:11 +0000 (UTC) Received: from t19.piap.pl (OSB1819.piap.pl [10.0.9.19]) by ni.piap.pl (Postfix) with ESMTPS id 10210C3EEAC9; Thu, 19 Mar 2026 12:45:41 +0100 (CET) DKIM-Filter: OpenDKIM Filter v2.11.0 ni.piap.pl 10210C3EEAC9 From: =?utf-8?Q?Krzysztof_Ha=C5=82asa?= To: Marek Vasut , Stefan Agner Cc: Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Frank Li , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , dri-devel@lists.freedesktop.org, imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: i.MX8MP: Fix HDMI LCDIF FIFO underruns Date: Thu, 19 Mar 2026 12:45:40 +0100 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" Running (and terminating) Weston on i.MX8MP sometimes produced black or grey screens. The LCDIF3 INT_STATUS_D0 register showed a FIFO underrun: 32FC6024: 1000002 The PANIC0_THRES register was set to: 32FC6238: AA0154 which apparently meant low =3D 2736 bytes (0xAA * 16 + 16), high =3D 5456 b= ytes (0x154 * 16 + 16). With this patch (based on NXP's driver) the watermarks are only 16 bytes higher (register values increased by 1) and the underruns are gone. Tested on Solidrun Hummingboard Mate with a 1080p60 HDMI display. Signed-off-by: Krzysztof Ha=C5=82asa --- a/drivers/gpu/drm/mxsfb/lcdif_kms.c +++ b/drivers/gpu/drm/mxsfb/lcdif_kms.c @@ -353,8 +353,8 @@ static void lcdif_enable_controller(struct lcdif_drm_pr= ivate *lcdif) u32 reg; =20 /* Set FIFO Panic watermarks, low 1/3, high 2/3 . */ - writel(FIELD_PREP(PANIC0_THRES_LOW_MASK, 1 * PANIC0_THRES_MAX / 3) | - FIELD_PREP(PANIC0_THRES_HIGH_MASK, 2 * PANIC0_THRES_MAX / 3), + writel(FIELD_PREP(PANIC0_THRES_LOW_MASK, DIV_ROUND_UP(1 * PANIC0_THRES_MA= X, 3)) | + FIELD_PREP(PANIC0_THRES_HIGH_MASK, DIV_ROUND_UP(2 * PANIC0_THRES_M= AX, 3)), lcdif->base + LCDC_V8_PANIC0_THRES); =20 /* --=20 Krzysztof "Chris" Ha=C5=82asa Sie=C4=87 Badawcza =C5=81ukasiewicz Przemys=C5=82owy Instytut Automatyki i Pomiar=C3=B3w PIAP Al. Jerozolimskie 202, 02-486 Warszawa