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 0/3] clk: divider: three exactness fixes (and a rant)
Date: Sat, 21 Feb 2015 11:40:22 +0100 [thread overview]
Message-ID: <1424515225-6929-1-git-send-email-u.kleine-koenig@pengutronix.de> (raw)
In-Reply-To: <20150221085620.GV19388@pengutronix.de>
Hello,
TLDR: only apply patch 1 and rip of CLK_DIVIDER_ROUND_CLOSEST.
I stared at clk-divider.c for some time now given Sascha's failing test
case. I found a fix for the failure (which happens to be what Sascha
suspected).
The other two patches fix problems only present when handling dividers
that have CLK_DIVIDER_ROUND_CLOSEST set. Note that these are still
heavily broken however. So having a 4bit-divider and a parent clk of
10000 (as in Sascha's test case) requesting
clk_set_rate(clk, 666)
sets the rate to 625 (div=15) instead of 667 (div=16). The reason is the
choice of parent_rate in clk_divider_bestdiv's loop is wrong for
CLK_DIVIDER_ROUND_CLOSEST (with and without patch 1). A fix here is
non-trivial and for sure more than one rate must be tested here. This is
complicated by the fact that clk_round_rate might return a value bigger
than the requested rate which convinces me (once more) that it's a bad
idea to allow that. Even if this was fixed for .round_rate,
clk_divider_set_rate is still broken because it also uses
div = DIV_ROUND_UP(parent_rate, rate);
to calculate the (pretended) best divider to get near rate.
Note this makes at least two reasons to remove support for
CLK_DIVIDER_ROUND_CLOSEST!
Instead I'd favour creating a function
clk_round_rate_nearest
as was suggested some time ago by Soren Brinkmann and me[1] that doesn't
need any clk type specific knowledge. This would mean that not the
divider (or clk in general) would have to know that returning a slightly
bigger rate than requested is OK but the caller which is fine (and even
better) in my eyes. This would simplify clk-divider.c (and probably
others) and give support for "nearest match" for all clock types without
type specific implementation. (Note that it might even make sense to use
a different metric for "nearest", instead of minimizing
abs(target - rate)
you might want to minimize
abs(target / rate - 1)
instead.
Converting the clk framework to 64 bit rates was discussed earlier
already, too, and I wonder if we should fix rounding issues (a bit) in
the same transition such that
clk_set_rate(clk, 333)
allows the clk to be set to 333.3333333333 Hz and let clk_get_rate
return 333 in this case.
Also I'd vote to return 0 or -ESOMETHING if a requested rate is too low
to be set. This would simplify some special casing I think and makes the
request
clk_round_rate(clk, x) <= x
consistent.
Best regards
Uwe
[1] https://lkml.org/lkml/2014/5/14/698
Uwe Kleine-König (3):
clk: divider: fix calculation of maximal parent rate for a given
divider
clk: divider: fix selection of divider when rounding to closest
clk: divider: fix calculation of initial best divider when rounding to
closest
drivers/clk/clk-divider.c | 27 +++++++++++++--------------
1 file changed, 13 insertions(+), 14 deletions(-)
--
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 ` Uwe Kleine-König [this message]
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 ` [PATCH 2/3] clk: divider: fix selection of divider when rounding to closest Uwe Kleine-König
2015-02-23 9:46 ` 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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