From patchwork Fri Feb 24 12:55:00 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Keeping X-Patchwork-Id: 9590055 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 79994601AE for ; Fri, 24 Feb 2017 12:56:02 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 419EA28756 for ; Fri, 24 Feb 2017 12:56:02 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 368042877F; Fri, 24 Feb 2017 12:56:02 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.1 required=2.0 tests=BAYES_00,DKIM_SIGNED, RCVD_IN_DNSWL_MED,T_DKIM_INVALID autolearn=ham version=3.3.1 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id EB70E28756 for ; Fri, 24 Feb 2017 12:56:01 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 6869F6EC3F; Fri, 24 Feb 2017 12:55:37 +0000 (UTC) X-Original-To: dri-devel@lists.freedesktop.org Delivered-To: dri-devel@lists.freedesktop.org Received: from metanate.com (dougal.metanate.com [90.155.101.14]) by gabe.freedesktop.org (Postfix) with ESMTPS id D4C2F6EC39 for ; Fri, 24 Feb 2017 12:55:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=simple/simple; d=metanate.com; s=stronger; h=References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From; bh=+VZg6oSJXgkgKext1YJRvvwHKl9Xu5mD45SztyE1gxI=; b=hVySqNaWK1PX16vHf0aaY/kXLbuWj5buqy2yyBKo2CqvNMqyvwAjqAP5U/QgOzJmGgsIyTjyuoIbL8+lNPRN5mW/6G5Cj3ll5+J8AVeVokPVUhHAhRwWSK1qxILjd4K78UtYHGOTIxCQPp+yooYWaObq1T5Qrcgk00d0ZUqkUsZlzUMS9N0wLAV/xrag7hkYhhr5CYEYXMfB8kvWWU8T1bH8mK2c7YMKJOaU1dYJnUfSVJvE2vWpvtMoiq5/yrxyOku2YzKaE+tz50tQVVI3NGfOB1YEfVfIyfBNZq5FIPnoGC6QJU8HIk2ZlE2XFh8fpL10zMh76zV/xCEyen8jCA==; Received: from brian ([192.168.88.1] helo=leela.metanate.com) by shrek.metanate.com with esmtpsa (TLSv1.2:DHE-RSA-AES128-GCM-SHA256:128) (Exim 4.83_RC2) (envelope-from ) id 1chFP2-0006ml-5m; Fri, 24 Feb 2017 12:55:16 +0000 From: John Keeping To: Mark Yao Subject: [PATCH v4 17/23] drm/rockchip: dw-mipi-dsi: improve PLL configuration Date: Fri, 24 Feb 2017 12:55:00 +0000 Message-Id: <20170224125506.21533-18-john@metanate.com> X-Mailer: git-send-email 2.12.0.rc0.230.gf625d4cdb9.dirty In-Reply-To: <20170224125506.21533-1-john@metanate.com> References: <20170224125506.21533-1-john@metanate.com> Cc: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-rockchip@lists.infradead.org, Chris Zhong , linux-arm-kernel@lists.infradead.org X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.18 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" X-Virus-Scanned: ClamAV using ClamSMTP The multiplication ratio for the PLL is required to be even due to the use of a "by 2 pre-scaler". Currently we are likely to end up with an odd multiplier even though there is an equivalent set of parameters with an even multiplier. For example, using the 324MHz bit rate with a reference clock of 24MHz we end up with M = 27, N = 2 whereas the example in the PHY databook gives M = 54, N = 4 for this bit rate and reference clock. By walking down through the available multiplier instead of up we are more likely to hit an even multiplier. With the above example we do now get M = 54, N = 4 as given by the databook. While doing this, change the loop limits to encode the actual limits on the divisor, which are: 40MHz >= (pllref / N) >= 5MHz Signed-off-by: John Keeping Reviewed-by: Sean Paul --- v4: - Add a comment explaining the limits so that it can be understood without finding the commit message above - Add Sean's Reviewed-by Unchanged in v3 Unchanged in v2 --- drivers/gpu/drm/rockchip/dw-mipi-dsi.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c index 9b6a60deb69e..e6b52c7cb5e3 100644 --- a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c +++ b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c @@ -518,7 +518,18 @@ static int dw_mipi_dsi_get_lane_bps(struct dw_mipi_dsi *dsi, pllref = DIV_ROUND_UP(clk_get_rate(dsi->pllref_clk), USEC_PER_SEC); tmp = pllref; - for (i = 1; i < 6; i++) { + /* + * The limits on the PLL divisor are: + * + * 5MHz <= (pllref / n) <= 40MHz + * + * we walk over these values in descreasing order so that if we hit + * an exact match for target_mbps it is more likely that "m" will be + * even. + * + * TODO: ensure that "m" is even after this loop. + */ + for (i = pllref / 5; i > (pllref / 40); i--) { pre = pllref / i; if ((tmp > (target_mbps % pre)) && (target_mbps / pre < 512)) { tmp = target_mbps % pre;