From patchwork Tue Sep 30 15:14:35 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "U. Artie Eoff" X-Patchwork-Id: 5003991 Return-Path: X-Original-To: patchwork-intel-gfx@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.19.201]) by patchwork2.web.kernel.org (Postfix) with ESMTP id D74B5BEEA6 for ; Tue, 30 Sep 2014 15:15:46 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 081EE2018E for ; Tue, 30 Sep 2014 15:15:46 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) by mail.kernel.org (Postfix) with ESMTP id B1928201F4 for ; Tue, 30 Sep 2014 15:15:43 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id E82686FF3B; Tue, 30 Sep 2014 08:15:42 -0700 (PDT) X-Original-To: intel-gfx@lists.freedesktop.org Delivered-To: intel-gfx@lists.freedesktop.org Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by gabe.freedesktop.org (Postfix) with ESMTP id 283DC6FF3B for ; Tue, 30 Sep 2014 08:15:42 -0700 (PDT) Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga101.fm.intel.com with ESMTP; 30 Sep 2014 08:14:39 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.04,626,1406617200"; d="scan'208";a="598831165" Received: from uaeoff-mobl10.amr.corp.intel.com ([10.255.88.128]) by fmsmga001.fm.intel.com with ESMTP; 30 Sep 2014 08:14:39 -0700 From: "U. Artie Eoff" To: intel-gfx@lists.freedesktop.org Date: Tue, 30 Sep 2014 08:14:35 -0700 Message-Id: <1412090076-4873-1-git-send-email-ullysses.a.eoff@intel.com> X-Mailer: git-send-email 1.9.3 Subject: [Intel-gfx] [PATCH 1/2] drm/i915: intel_backlight scale() math WA X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" X-Spam-Status: No, score=-4.9 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_MED, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Improper truncated integer division in the scale() function causes actual_brightness != brightness. This (partial) work-around should be sufficient for a majority of use-cases, but it is by no means a complete solution. TODO: Determine how best to scale "user" values to "hw" values, and vice-versa, when the ranges are of different sizes. That would be a buggy scenario even with this work-around. The issue was introduced in the following (v3.17-rc1) commit: 6dda730 drm/i915: respect the VBT minimum backlight brightness OTC-Jira: VIZ-4395 v2: (thanks to Chris Wilson) clarify commit message, use rounded division macro v3: -DIV_ROUND_CLOSEST() fails to build with CONFIG_X86_32=y. (Jani) -Use DIV_ROUND_CLOSEST_ULL() instead. (Damien) -v1 and v2 originally authored by Joe Konno. v4: Add reference to issue report in commit message. Signed-off-by: U. Artie Eoff --- drivers/gpu/drm/i915/intel_panel.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c index f17ada3..f7da913 100644 --- a/drivers/gpu/drm/i915/intel_panel.c +++ b/drivers/gpu/drm/i915/intel_panel.c @@ -398,6 +398,9 @@ intel_panel_detect(struct drm_device *dev) } } +#define DIV_ROUND_CLOSEST_ULL(ll, d) \ +({ unsigned long long _tmp = (ll)+(d)/2; do_div(_tmp, d); _tmp; }) + /** * scale - scale values from one range to another * @@ -419,9 +422,8 @@ static uint32_t scale(uint32_t source_val, source_val = clamp(source_val, source_min, source_max); /* avoid overflows */ - target_val = (uint64_t)(source_val - source_min) * - (target_max - target_min); - do_div(target_val, source_max - source_min); + target_val = DIV_ROUND_CLOSEST_ULL((uint64_t)(source_val - source_min) * + (target_max - target_min), source_max - source_min); target_val += target_min; return target_val;