From patchwork Mon Aug 28 15:59:08 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Michael Tretter X-Patchwork-Id: 13368135 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2B9E7C83F11 for ; Mon, 28 Aug 2023 15:59:29 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id A659610E30C; Mon, 28 Aug 2023 15:59:19 +0000 (UTC) Received: from metis.ext.pengutronix.de (metis.ext.pengutronix.de [IPv6:2001:67c:670:201:290:27ff:fe1d:cc33]) by gabe.freedesktop.org (Postfix) with ESMTPS id 1C9F010E309 for ; Mon, 28 Aug 2023 15:59:14 +0000 (UTC) Received: from dude05.red.stw.pengutronix.de ([2a0a:edc0:0:1101:1d::54]) by metis.ext.pengutronix.de with esmtp (Exim 4.92) (envelope-from ) id 1qaee0-0005pk-3q; Mon, 28 Aug 2023 17:59:12 +0200 From: Michael Tretter Date: Mon, 28 Aug 2023 17:59:08 +0200 Subject: [PATCH 3/5] drm/bridge: samsung-dsim: update PLL reference clock MIME-Version: 1.0 Message-Id: <20230818-samsung-dsim-v1-3-b39716db6b7a@pengutronix.de> References: <20230818-samsung-dsim-v1-0-b39716db6b7a@pengutronix.de> In-Reply-To: <20230818-samsung-dsim-v1-0-b39716db6b7a@pengutronix.de> To: Inki Dae , Jagan Teki , Marek Szyprowski , Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , David Airlie , Daniel Vetter X-Mailer: b4 0.12.0 X-SA-Exim-Connect-IP: 2a0a:edc0:0:1101:1d::54 X-SA-Exim-Mail-From: m.tretter@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: dri-devel@lists.freedesktop.org X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kernel@pengutronix.de, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Michael Tretter Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" The PLL requires a clock between 2 MHz and 30 MHz after the pre-divider. The reference clock for the PLL may change due to changes to it's parent clock. Thus, the frequency may be out of range or unsuited for generating the high speed clock for MIPI DSI. Try to keep the pre-devider small, and set the reference clock close to 30 MHz before recalculating the PLL configuration. Use a divider with a power of two for the reference clock as this seems to work best in my tests. Signed-off-by: Michael Tretter Reviewed-by: Marco Felsch --- drivers/gpu/drm/bridge/samsung-dsim.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c index da90c2038042..4de6e4f116db 100644 --- a/drivers/gpu/drm/bridge/samsung-dsim.c +++ b/drivers/gpu/drm/bridge/samsung-dsim.c @@ -611,10 +611,21 @@ static unsigned long samsung_dsim_set_pll(struct samsung_dsim *dsi, u16 m; u32 reg; - if (dsi->pll_clk) + if (dsi->pll_clk) { + /* + * Ensure that the reference clock is generated with a power of + * two divider from its parent, but close to the PLLs upper + * limit of the valid range of 2 MHz to 30 MHz. + */ + fin = clk_get_rate(clk_get_parent(dsi->pll_clk)); + while (fin > 30 * MHZ) + fin = fin / 2; + clk_set_rate(dsi->pll_clk, fin); + fin = clk_get_rate(dsi->pll_clk); - else + } else { fin = dsi->pll_clk_rate; + } dev_dbg(dsi->dev, "PLL ref clock freq %lu\n", fin); fout = samsung_dsim_pll_find_pms(dsi, fin, freq, &p, &m, &s);