Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756678AbbBQKcy (ORCPT ); Tue, 17 Feb 2015 05:32:54 -0500 Received: from metis.ext.pengutronix.de ([92.198.50.35]:47890 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754914AbbBQKcw (ORCPT ); Tue, 17 Feb 2015 05:32:52 -0500 Date: Tue, 17 Feb 2015 11:32:24 +0100 From: Sascha Hauer To: Tomi Valkeinen Cc: Russell King - ARM Linux , Liu Ying , dri-devel@lists.freedesktop.org, stefan.wahren@i2se.com, devicetree@vger.kernel.org, kernel@pengutronix.de, sboyd@codeaurora.org, linux-kernel@vger.kernel.org, a.hajda@samsung.com, andy.yan@rock-chips.com, mturquette@linaro.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH RFC v9 01/20] clk: divider: Correct parent clk round rate if no bestdiv is normally found Message-ID: <20150217103224.GS12209@pengutronix.de> References: <1423720903-24806-1-git-send-email-Ying.Liu@freescale.com> <1423720903-24806-2-git-send-email-Ying.Liu@freescale.com> <20150212093356.GR12209@pengutronix.de> <20150212103944.GA1290@victor> <20150212122405.GW12209@pengutronix.de> <20150212125646.GT8656@n2100.arm.linux.org.uk> <20150212134131.GX12209@pengutronix.de> <54DE0BB8.7070004@ti.com> <20150213185713.GA12209@pengutronix.de> <54E1D1F5.2050603@ti.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54E1D1F5.2050603@ti.com> X-Sent-From: Pengutronix Hildesheim X-URL: http://www.pengutronix.de/ X-IRC: #ptxdist @freenode X-Accept-Language: de,en X-Accept-Content-Type: text/plain X-Uptime: 11:24:30 up 124 days, 21:38, 69 users, load average: 0.00, 0.03, 0.05 User-Agent: Mutt/1.5.21 (2010-09-15) X-SA-Exim-Connect-IP: 2001:67c:670:100:1d::c0 X-SA-Exim-Mail-From: sha@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5880 Lines: 166 On Mon, Feb 16, 2015 at 01:18:13PM +0200, Tomi Valkeinen wrote: > On 13/02/15 20:57, Sascha Hauer wrote: > > On Fri, Feb 13, 2015 at 04:35:36PM +0200, Tomi Valkeinen wrote: > >> On 12/02/15 15:41, Sascha Hauer wrote: > >> > >>> Tomis patch is based on the assumption that clk_set_rate(clk_round_rate(rate)) > >>> is equal to clk_round_rate(rate). So when this assumption is wrong then > >>> it should simply be reverted. > >> > >> When is it not equal? > >> > >> I agree that doing clk_set_rate(clk, clk_round_rate(clk, rate)) is > >> pointless, but shouldn't it still work? > >> > >> And we can forget about clk_round_rate. Without my patch, this would > >> behave oddly also: > >> > >> rate = clk_get_rate(clk); > >> clk_set_rate(clk, rate); > >> > >> The end result could be something else than 'rate'. > > > > I agree that it's a bit odd, but I think it has to be like this. > > Consider that you request a rate of 100Hz, but the clock can only > > produce 99.5Hz, so due to rounding clk_round_rate() returns 99Hz. > > Now when you request 99Hz from clk_set_rate() the 99.5Hz value > > can't be used because it's too high. > > Would that problem better be fixed by changing the clock driver so that > when asked for 99Hz, it would look for rates less than 100Hz? > > I think the old behavior was so odd that I would call it broken, so I > hope the current problems can be fixed via some other ways than breaking > it again. I gave it a try, but so far I have no idea how to implement the divider correctly and bullet proof. What I have so far is a test which creates some cascaded dividers and sets rates on them. The test iterates over the frequency range and a) calls clk_round_rate with the iterator, b) sets the clk to the iterator, c) sets the clk to the rounded rate. Be prepared for surprises and try to fix the results... I failed for now and wonder if the approach to the divider is wrong. Sascha >From 58a46b16d4b67d5cd7df4af6deb5b96e19afe230 Mon Sep 17 00:00:00 2001 From: Sascha Hauer Date: Tue, 17 Feb 2015 11:24:10 +0100 Subject: [PATCH] clk: clk-divider: Add a simple test for dividers Signed-off-by: Sascha Hauer --- drivers/clk/clk-divider.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 86 insertions(+) diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c index c0a842b..cd66625 100644 --- a/drivers/clk/clk-divider.c +++ b/drivers/clk/clk-divider.c @@ -463,3 +463,89 @@ struct clk *clk_register_divider_table(struct device *dev, const char *name, width, clk_divider_flags, table, lock); } EXPORT_SYMBOL_GPL(clk_register_divider_table); + +/* + * Simple test of dividers. Try to set rates between 1 and 10000Hz and + * - get output of clk_round_rate() + * - set the current target rate, get the rate + * - set the rate to the rounded rate, get the rate + * + * Whenever a value changed print the results + */ +static void clktest_one(struct clk *clk) +{ + int i, ret; + unsigned long roundsetrate, last_roundsetrate = 0; + unsigned long roundrate, last_roundrate = 0; + unsigned long setrate, last_setrate = 0; + + for (i = 1; i < 10000; i++) { + roundrate = clk_round_rate(clk, i); + + clk_set_rate(clk, i); + setrate = clk_get_rate(clk); + + ret = clk_set_rate(clk, roundrate); + if (ret) { + printk("clkdivtest: Failed to set rate: %d\n", ret); + return; + } + + roundsetrate = clk_get_rate(clk); + + if (last_roundsetrate != roundsetrate || + last_roundrate != roundrate || + last_setrate != setrate) + printk("target rate: %4d rounded: %4ld set: %4ld round/set: %4ld\n", + i, roundrate, setrate, roundsetrate); + + last_roundsetrate = roundsetrate; + last_roundrate = roundrate; + last_setrate = setrate; + } +} + +static int clktest(void) +{ + u32 reg_div1 = 0; + u32 reg_div2 = 0; + u32 reg_div3 = 0; + struct clk *clktest_base = ERR_PTR(-ENODEV); + struct clk *clktest_div1 = ERR_PTR(-ENODEV); + struct clk *clktest_div2 = ERR_PTR(-ENODEV); + struct clk *clktest_div3 = ERR_PTR(-ENODEV); + + clktest_base = clk_register_fixed_rate(NULL, "clktest_base", NULL, 0, 10000); + clktest_div1 = clk_register_divider(NULL, "clktest_div1", "clktest_base", + 0, ®_div1, 0, 4, 0, NULL); + clktest_div2 = clk_register_divider(NULL, "clktest_div2", "clktest_div1", + CLK_SET_RATE_PARENT, ®_div2, 0, 4, 0, NULL); + clktest_div3 = clk_register_divider(NULL, "clktest_div3", "clktest_div2", + CLK_SET_RATE_PARENT, ®_div3, 0, 4, 0, NULL); + + if (IS_ERR(clktest_base) || IS_ERR(clktest_div1) || + IS_ERR(clktest_div2) || IS_ERR(clktest_div3)) { + printk("clkdivtest: Failed to register clocks\n"); + goto err_out; + } + + printk("------------------ Single divider, fin=10000Hz ------------------\n"); + clktest_one(clktest_div1); + printk("--------------- two cascaded dividers, fin=10000Hz --------------\n"); + clktest_one(clktest_div2); + printk("-------------- three cascaded dividers, fin=10000Hz -------------\n"); + clktest_one(clktest_div3); + +err_out: + if (!IS_ERR(clktest_base)) + clk_unregister(clktest_base); + if (!IS_ERR(clktest_div1)) + clk_unregister(clktest_div1); + if (!IS_ERR(clktest_div2)) + clk_unregister(clktest_div2); + if (!IS_ERR(clktest_div3)) + clk_unregister(clktest_div3); + + return 0; +} +late_initcall(clktest); -- 2.1.4 -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 | -- 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/