From patchwork Thu Jan 9 22:05:47 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: "Lisovskiy, Stanislav" X-Patchwork-Id: 11326415 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 658791398 for ; Thu, 9 Jan 2020 22:08:11 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 4D60E2080D for ; Thu, 9 Jan 2020 22:08:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4D60E2080D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=intel-gfx-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id CBE3F6E972; Thu, 9 Jan 2020 22:08:10 +0000 (UTC) X-Original-To: intel-gfx@lists.freedesktop.org Delivered-To: intel-gfx@lists.freedesktop.org Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by gabe.freedesktop.org (Postfix) with ESMTPS id 2E2CE6E972 for ; Thu, 9 Jan 2020 22:08:09 +0000 (UTC) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 09 Jan 2020 14:08:08 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,414,1571727600"; d="scan'208";a="423390827" Received: from slisovsk-lenovo-ideapad-720s-13ikb.fi.intel.com ([10.237.72.89]) by fmsmga006.fm.intel.com with ESMTP; 09 Jan 2020 14:08:06 -0800 From: Stanislav Lisovskiy To: intel-gfx@lists.freedesktop.org Date: Fri, 10 Jan 2020 00:05:47 +0200 Message-Id: <20200109220547.23817-1-stanislav.lisovskiy@intel.com> X-Mailer: git-send-email 2.24.1.485.gad05a3d8e5 MIME-Version: 1.0 Subject: [Intel-gfx] [PATCH v3] drm/i915: Bump up CDCLK to eliminate underruns on TGL X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" There seems to be some undocumented bandwidth bottleneck/dependency which scales with CDCLK, causing FIFO underruns when CDCLK is too low, even when it's correct from BSpec point of view. Currently for TGL platforms we calculate min_cdclk initially based on pixel_rate divided by 2, accounting for also plane requirements, however in some cases the lowest possible CDCLK doesn't work and causing the underruns. We've found experimentally that raising cdclk to at least pixel_rate (rather than pixel_rate/2) eliminates these underruns, so let's use this as a temporary workaround until the hardware team can suggest a more precise remedy. Explicitly stating here that this seems to be currently rather a Hack, than final solution. v2: Use clamp operation instead of min(Matt Roper) v3: - Fixed commit message(Matt Roper) - Now using pixel_rate instead of max_cdclk(Jani Nikula) - Switched to max from clamp(Ville Syrjälä) Hopefully this hybrid satisfies everyone :) Reviewed-by: Matt Roper Signed-off-by: Stanislav Lisovskiy Closes: https://gitlab.freedesktop.org/drm/intel/issues/402 --- drivers/gpu/drm/i915/display/intel_cdclk.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/drivers/gpu/drm/i915/display/intel_cdclk.c b/drivers/gpu/drm/i915/display/intel_cdclk.c index 7d1ab1e5b7c3..0ce5926006ca 100644 --- a/drivers/gpu/drm/i915/display/intel_cdclk.c +++ b/drivers/gpu/drm/i915/display/intel_cdclk.c @@ -2004,6 +2004,18 @@ int intel_crtc_compute_min_cdclk(const struct intel_crtc_state *crtc_state) /* Account for additional needs from the planes */ min_cdclk = max(intel_planes_min_cdclk(crtc_state), min_cdclk); + /* + * HACK. Currently for TGL platforms we calculate + * min_cdclk initially based on pixel_rate divided + * by 2, accounting for also plane requirements, + * however in some cases the lowest possible CDCLK + * doesn't work and causing the underruns. + * Explicitly stating here that this seems to be currently + * rather a Hack, than final solution. + */ + if (IS_TIGERLAKE(dev_priv)) + min_cdclk = max(min_cdclk, (int)crtc_state->pixel_rate); + if (min_cdclk > dev_priv->max_cdclk_freq) { DRM_DEBUG_KMS("required cdclk (%d kHz) exceeds max (%d kHz)\n", min_cdclk, dev_priv->max_cdclk_freq);