From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Mike Turquette <mturquette@linaro.org>,
Stephen Boyd <sboyd@codeaurora.org>
Cc: kernel@pengutronix.de, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
"Sören Brinkmann" <soren.brinkmann@xilinx.com>
Subject: [PATCH 2/3] clk: divider: fix selection of divider when rounding to closest
Date: Sat, 21 Feb 2015 11:40:24 +0100 [thread overview]
Message-ID: <1424515225-6929-3-git-send-email-u.kleine-koenig@pengutronix.de> (raw)
In-Reply-To: <1424515225-6929-1-git-send-email-u.kleine-koenig@pengutronix.de>
It's an invalid approach to assume that among two divider values
the one nearer the exact divider is the better one.
Assume a parent rate of 1000 Hz, a divider with CLK_DIVIDER_POWER_OF_TWO
and a target rate of 89 Hz. The exact divider is ~ 11.236 so 8 and 16
are the candidates to choose from yielding rates 125 Hz and 62.5 Hz
respectivly. While 8 is nearer to 11.236 than 16 is, the latter is still
the better divider as 62.5 is nearer to 89 than 125 is.
Fixes: 774b514390b1 (clk: divider: Add round to closest divider)
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
---
drivers/clk/clk-divider.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/clk/clk-divider.c b/drivers/clk/clk-divider.c
index fbd9e8270791..66a6211b8834 100644
--- a/drivers/clk/clk-divider.c
+++ b/drivers/clk/clk-divider.c
@@ -202,6 +202,7 @@ static int _div_round_closest(struct clk_divider *divider,
unsigned long parent_rate, unsigned long rate)
{
int up, down, div;
+ unsigned long up_rate, down_rate;
up = down = div = DIV_ROUND_CLOSEST(parent_rate, rate);
@@ -213,7 +214,10 @@ static int _div_round_closest(struct clk_divider *divider,
down = _round_down_table(divider->table, div);
}
- return (up - div) <= (div - down) ? up : down;
+ up_rate = DIV_ROUND_UP(parent_rate, up);
+ down_rate = DIV_ROUND_UP(parent_rate, down);
+
+ return (rate - up_rate) <= (down_rate - rate) ? up : down;
}
static int _div_round(struct clk_divider *divider, unsigned long parent_rate,
--
2.1.4
next prev parent reply other threads:[~2015-02-21 10:40 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-12 6:01 [PATCH RFC v9 00/20] Add support for i.MX MIPI DSI DRM driver Liu Ying
2015-02-12 6:01 ` [PATCH RFC v9 01/20] clk: divider: Correct parent clk round rate if no bestdiv is normally found Liu Ying
2015-02-12 9:33 ` Sascha Hauer
2015-02-12 10:39 ` Liu Ying
2015-02-12 12:24 ` Sascha Hauer
2015-02-12 12:56 ` Russell King - ARM Linux
2015-02-12 13:41 ` Sascha Hauer
2015-02-12 14:06 ` Liu Ying
2015-02-13 2:58 ` Liu Ying
2015-02-13 2:58 ` Travis
2015-02-13 14:35 ` Tomi Valkeinen
2015-02-13 18:57 ` Sascha Hauer
2015-02-16 11:18 ` Tomi Valkeinen
2015-02-17 10:32 ` Sascha Hauer
2015-02-16 11:27 ` Russell King - ARM Linux
2015-02-20 19:13 ` Mike Turquette
2015-02-20 19:20 ` Russell King - ARM Linux
2015-02-21 8:56 ` Uwe Kleine-König
2015-02-21 10:40 ` [PATCH 0/3] clk: divider: three exactness fixes (and a rant) Uwe Kleine-König
2015-02-21 10:40 ` [PATCH 1/3] clk: divider: fix calculation of maximal parent rate for a given divider Uwe Kleine-König
2015-02-23 7:32 ` Sascha Hauer
2015-03-05 8:35 ` Uwe Kleine-König
2015-02-21 10:40 ` Uwe Kleine-König [this message]
2015-02-23 9:46 ` [PATCH 2/3] clk: divider: fix selection of divider when rounding to closest Maxime Coquelin
2015-02-21 10:40 ` [PATCH 3/3] clk: divider: fix calculation of initial best " Uwe Kleine-König
2015-02-23 9:42 ` Maxime Coquelin
2015-02-23 7:23 ` [PATCH 0/3] clk: divider: three exactness fixes (and a rant) Sascha Hauer
2015-03-06 18:57 ` Mike Turquette
2015-03-06 19:28 ` Uwe Kleine-König
2015-03-06 19:40 ` Stephen Boyd
2015-03-09 9:58 ` Philipp Zabel
2015-03-09 19:05 ` Stephen Boyd
2015-03-09 20:23 ` Uwe Kleine-König
2015-03-09 21:07 ` Mike Turquette
2015-03-09 21:58 ` Uwe Kleine-König
2015-03-09 22:40 ` Stephen Boyd
2015-03-09 23:34 ` Uwe Kleine-König
2015-03-12 1:21 ` Stephen Boyd
2015-03-12 8:57 ` Philipp Zabel
2015-03-13 7:50 ` Uwe Kleine-König
2015-03-13 8:13 ` Philipp Zabel
2015-03-06 19:44 ` Stephen Boyd
2015-03-06 21:09 ` Uwe Kleine-König
2015-02-12 6:01 ` [PATCH RFC v9 02/20] ARM: imx6q: Add GPR3 MIPI muxing control register field shift bits definition Liu Ying
2015-02-12 6:01 ` [PATCH RFC v9 03/20] ARM: imx6q: clk: Add the video_27m clock Liu Ying
2015-02-12 6:01 ` [PATCH RFC v9 04/20] ARM: imx6q: clk: Change hdmi_isfr clock's parent to be " Liu Ying
2015-02-12 6:01 ` [PATCH RFC v9 05/20] ARM: imx6q: clk: Change hsi_tx clock to be a shared clock gate Liu Ying
2015-02-12 6:01 ` [PATCH RFC v9 06/20] ARM: imx6q: clk: Add support for mipi_core_cfg clock as " Liu Ying
2015-02-12 6:01 ` [PATCH RFC v9 07/20] ARM: imx6q: clk: Add support for mipi_ipg " Liu Ying
2015-02-12 6:01 ` [PATCH RFC v9 08/20] ARM: dts: imx6qdl: Move existing MIPI DSI ports into a new 'ports' node Liu Ying
2015-02-12 6:01 ` [PATCH RFC v9 09/20] drm/dsi: Add a helper to get bits per pixel of MIPI DSI pixel format Liu Ying
2015-02-12 9:26 ` Daniel Vetter
2015-02-13 5:01 ` Liu Ying
2015-03-03 11:07 ` Philipp Zabel
2015-04-03 3:28 ` Liu Ying
2015-04-09 7:10 ` Thierry Reding
2015-02-12 6:01 ` [PATCH RFC v9 10/20] Documentation: dt-bindings: Add bindings for Synopsys DW MIPI DSI DRM bridge driver Liu Ying
2015-02-12 6:01 ` [PATCH RFC v9 11/20] drm/bridge: Add Synopsys DesignWare MIPI DSI host controller driver Liu Ying
2015-04-09 8:43 ` Thierry Reding
2015-04-16 5:39 ` Archit Taneja
2015-04-22 12:13 ` Heiko Stübner
2015-02-12 6:01 ` [PATCH RFC v9 12/20] Documentation: dt-bindings: Add bindings for i.MX specific Synopsys DW MIPI DSI driver Liu Ying
2015-02-12 6:01 ` [PATCH RFC v9 13/20] drm: imx: Support Synopsys DesignWare MIPI DSI host controller Liu Ying
2015-02-12 6:01 ` [PATCH RFC v9 14/20] Documentation: dt-bindings: Add bindings for Himax HX8369A DRM panel driver Liu Ying
2015-04-09 7:20 ` Thierry Reding
2015-02-12 6:01 ` [PATCH RFC v9 15/20] drm: panel: Add support for Himax HX8369A MIPI DSI panel Liu Ying
2015-04-09 8:09 ` Thierry Reding
2015-02-12 6:01 ` [PATCH RFC v9 16/20] ARM: dtsi: imx6qdl: Add support for MIPI DSI host controller Liu Ying
2015-02-12 6:01 ` [PATCH RFC v9 17/20] ARM: dts: imx6qdl-sabresd: Add support for TRULY TFT480800-16-E MIPI DSI panel Liu Ying
2015-02-12 6:01 ` [PATCH RFC v9 18/20] ARM: imx_v6_v7_defconfig: Cleanup for imx drm being moved out of staging Liu Ying
2015-02-12 6:01 ` [PATCH RFC v9 19/20] ARM: imx_v6_v7_defconfig: Add support for MIPI DSI host controller Liu Ying
2015-02-12 6:01 ` [PATCH RFC v9 20/20] ARM: imx_v6_v7_defconfig: Add support for Himax HX8369A panel Liu Ying
2015-03-02 13:24 ` [PATCH RFC v9 00/20] Add support for i.MX MIPI DSI DRM driver Shawn Guo
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