Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756567Ab3I2Tnt (ORCPT ); Sun, 29 Sep 2013 15:43:49 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:59565 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755909Ab3I2T3C (ORCPT ); Sun, 29 Sep 2013 15:29:02 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Aaron Lu , Jani Nikula , Daniel Vetter Subject: [ 22/71] drm/i915: try not to lose backlight CBLV precision Date: Sun, 29 Sep 2013 12:27:34 -0700 Message-Id: <20130929192645.039982757@linuxfoundation.org> X-Mailer: git-send-email 1.8.4.6.g82e253f.dirty In-Reply-To: <20130929192643.539596256@linuxfoundation.org> References: <20130929192643.539596256@linuxfoundation.org> User-Agent: quilt/0.60-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1986 Lines: 52 3.11-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jani Nikula commit cac6a5ae0118832936eb162ec4cedb30f2422bcc upstream. ACPI has _BCM and _BQC methods to set and query the backlight brightness, respectively. The ACPI opregion has variables BCLP and CBLV to hold the requested and current backlight brightness, respectively. The BCLP variable has range 0..255 while the others have range 0..100. This means the _BCM method has to scale the brightness for BCLP, and the gfx driver has to scale the requested value back for CBLV. If the _BQC method uses the CBLV variable (apparently some implementations do, some don't) for current backlight level reporting, there's room for rounding errors. Use DIV_ROUND_UP for scaling back to CBLV to get back to the same values that were passed to _BCM, presuming the _BCM simply uses bclp = (in * 255) / 100 for scaling to BCLP. Reference: https://gist.github.com/aaronlu/6314920 Reported-by: Aaron Lu Signed-off-by: Jani Nikula Reviewed-by: Aaron Lu Signed-off-by: Daniel Vetter Signed-off-by: Greg Kroah-Hartman --- drivers/gpu/drm/i915/intel_opregion.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/drivers/gpu/drm/i915/intel_opregion.c +++ b/drivers/gpu/drm/i915/intel_opregion.c @@ -173,7 +173,7 @@ static u32 asle_set_backlight(struct drm return ASLE_BACKLIGHT_FAILED; intel_panel_set_backlight(dev, bclp, 255); - iowrite32((bclp*0x64)/0xff | ASLE_CBLV_VALID, &asle->cblv); + iowrite32(DIV_ROUND_UP(bclp * 100, 255) | ASLE_CBLV_VALID, &asle->cblv); return 0; } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/