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: 9590173 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 53E6C601AE for ; Fri, 24 Feb 2017 13:05:39 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 1642E28753 for ; Fri, 24 Feb 2017 13:05:39 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 0B1FB2875C; Fri, 24 Feb 2017 13:05:39 +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=-1.9 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID autolearn=unavailable version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [65.50.211.133]) (using TLSv1.2 with cipher AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 9C21128753 for ; Fri, 24 Feb 2017 13:05:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:MIME-Version:Cc:List-Subscribe: List-Help:List-Post:List-Archive:List-Unsubscribe:List-Id:References: In-Reply-To:Message-Id:Date:Subject:To:From:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Owner; bh=vtduZOSjB/pxqYyKMKLbhtBtXPHAVd84TvfAj7+JR0U=; b=jiueEcxwKJfcey1ztHi4QR1XTJ 8XyorYLcdZm4usXoOjHQER0Ul5OP7t7bph8FUTdI8ABsD9BomcJIAdV5OIH40I/o26Q5W++AVlYb5 IlI+jYXP95nWnGgtOsThCOxcge0ZNPVNVbWWz71FjA2NO6K4lC5Cub1sbU4u8rKwshvafbVqZ1h0q +ho/zE2WhDgYhDQeN+8zxhfp/VyemqrV0Wn5ABsPtjwDVRMkQvjZ5SdeVjh96mVemp7gSEPKQylWP ikSR+GlfUcqjVBvjXIrocdYU7seC0QgqN4xWP8wJmU4QIEUuRwH5tsl9T0p/yS0aModUBzuwUWcRa rRh/Idgw==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.87 #1 (Red Hat Linux)) id 1chFYz-00063g-Sz; Fri, 24 Feb 2017 13:05:33 +0000 Received: from dougal.metanate.com ([90.155.101.14] helo=metanate.com) by bombadil.infradead.org with esmtps (Exim 4.87 #1 (Red Hat Linux)) id 1chFPb-0006R6-N1; Fri, 24 Feb 2017 12:55:57 +0000 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> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20170224_045552_188046_7D1B414B X-CRM114-Status: GOOD ( 11.36 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-rockchip@lists.infradead.org, Sean Paul , Chris Zhong , John Keeping , linux-arm-kernel@lists.infradead.org MIME-Version: 1.0 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org 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;