From patchwork Mon Apr 28 03:19:29 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Aaron Lu X-Patchwork-Id: 4074641 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 F30FCBFF02 for ; Mon, 28 Apr 2014 03:18:44 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id E30E320204 for ; Mon, 28 Apr 2014 03:18:43 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) by mail.kernel.org (Postfix) with ESMTP id 8A2B3201DD for ; Mon, 28 Apr 2014 03:18:42 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 05A3D6E5C5; Sun, 27 Apr 2014 20:18:41 -0700 (PDT) X-Original-To: intel-gfx@lists.freedesktop.org Delivered-To: intel-gfx@lists.freedesktop.org Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by gabe.freedesktop.org (Postfix) with ESMTP id 578196E5C5; Sun, 27 Apr 2014 20:18:39 -0700 (PDT) Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga102.jf.intel.com with ESMTP; 27 Apr 2014 20:13:45 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.97,940,1389772800"; d="scan'208";a="530678615" Received: from aaronlu.sh.intel.com ([10.239.37.56]) by orsmga002.jf.intel.com with ESMTP; 27 Apr 2014 20:18:37 -0700 Message-ID: <535DC8C1.5090407@intel.com> Date: Mon, 28 Apr 2014 11:19:29 +0800 From: Aaron Lu MIME-Version: 1.0 To: Daniel Vetter , Jani Nikula Cc: "intel-gfx@lists.freedesktop.org" , Nico Schottelius , "dri-devel@lists.freedesktop.org" Subject: [Intel-gfx] [PATCH] drm/i915: restore backlight precision when converting from opregion 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: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" X-Spam-Status: No, score=-4.8 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 When we set backlight on behalf of ACPI opregion, we will convert the backlight value in the 0-255 range defined in opregion to the actual hardware level. Commit 22505b82a2 (drm/i915: avoid brightness overflow when doing scale) is meant to fix the overflow problem when doing the conversion, but it also caused a problem that the converted hardware level doesn't quite represent the intended value: say user wants maximum backlight level(255 in opregion's range), then we will calculate the actual hardware level to be: level = freq / max * level, where freq is the hardware's max backlight level(937 on an user's box), and max and level are all 255. The converted value should be 937 but the above calculation will yield 765. To fix this issue, just use 64 bits to do the calculation to keep the precision and avoid overflow at the same time. Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=72491 Reported-and-tested-by: Nico Schottelius Signed-off-by: Aaron Lu --- drivers/gpu/drm/i915/intel_panel.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c index a953b081ee38..bdd2f24b7a6b 100644 --- a/drivers/gpu/drm/i915/intel_panel.c +++ b/drivers/gpu/drm/i915/intel_panel.c @@ -502,10 +502,7 @@ void intel_panel_set_backlight(struct intel_connector *connector, u32 level, /* scale to hardware max, but be careful to not overflow */ freq = panel->backlight.max; - if (freq < max) - level = level * freq / max; - else - level = freq / max * level; + level = (u64)level * freq / max; panel->backlight.level = level; if (panel->backlight.device)