LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Stephen Boyd <sboyd@codeaurora.org>,
	linux-kernel@vger.kernel.org, heikki.krogerus@linux.intel.com
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Subject: [PATCH v2 1/2] clk: fractional-divider: switch to rational best approximation
Date: Mon, 30 Mar 2015 21:57:48 +0300	[thread overview]
Message-ID: <1427741869-239562-2-git-send-email-andriy.shevchenko@linux.intel.com> (raw)
In-Reply-To: <1427741869-239562-1-git-send-email-andriy.shevchenko@linux.intel.com>

This patch converts the code to use rational best approximation algorithm which
is more precise.

Suggested-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/clk/Kconfig                  |  3 +--
 drivers/clk/clk-fractional-divider.c | 39 ++++++++++++++----------------------
 2 files changed, 16 insertions(+), 26 deletions(-)

diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig
index 0b474a0..46d90a9 100644
--- a/drivers/clk/Kconfig
+++ b/drivers/clk/Kconfig
@@ -14,6 +14,7 @@ config COMMON_CLK
 	select HAVE_CLK_PREPARE
 	select CLKDEV_LOOKUP
 	select SRCU
+	select RATIONAL
 	---help---
 	  The common clock framework is a single definition of struct
 	  clk, useful across many platforms, as well as an
@@ -63,7 +64,6 @@ config COMMON_CLK_SI5351
 	tristate "Clock driver for SiLabs 5351A/B/C"
 	depends on I2C
 	select REGMAP_I2C
-	select RATIONAL
 	---help---
 	  This driver supports Silicon Labs 5351A/B/C programmable clock
 	  generators.
@@ -139,7 +139,6 @@ config COMMON_CLK_CDCE706
 	tristate "Clock driver for TI CDCE706 clock synthesizer"
 	depends on I2C
 	select REGMAP_I2C
-	select RATIONAL
 	---help---
 	  This driver supports TI CDCE706 programmable 3-PLL clock synthesizer.
 
diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk-fractional-divider.c
index 6aa72d9..9c53704 100644
--- a/drivers/clk/clk-fractional-divider.c
+++ b/drivers/clk/clk-fractional-divider.c
@@ -7,13 +7,14 @@
  *
  * Adjustable fractional divider clock implementation.
  * Output rate = (m / n) * parent_rate.
+ * Uses rational best approximation algorithm.
  */
 
 #include <linux/clk-provider.h>
 #include <linux/module.h>
 #include <linux/device.h>
 #include <linux/slab.h>
-#include <linux/gcd.h>
+#include <linux/rational.h>
 
 #define to_clk_fd(_hw) container_of(_hw, struct clk_fractional_divider, hw)
 
@@ -21,9 +22,9 @@ static unsigned long clk_fd_recalc_rate(struct clk_hw *hw,
 					unsigned long parent_rate)
 {
 	struct clk_fractional_divider *fd = to_clk_fd(hw);
+	unsigned long m, n;
 	unsigned long flags = 0;
-	u32 val, m, n;
-	u64 ret;
+	u32 val;
 
 	if (fd->lock)
 		spin_lock_irqsave(fd->lock, flags);
@@ -39,30 +40,22 @@ static unsigned long clk_fd_recalc_rate(struct clk_hw *hw,
 	if (!n || !m)
 		return parent_rate;
 
-	ret = (u64)parent_rate * m;
-	do_div(ret, n);
-
-	return ret;
+	return mult_frac(parent_rate, m, n);
 }
 
 static long clk_fd_round_rate(struct clk_hw *hw, unsigned long rate,
-			      unsigned long *prate)
+			      unsigned long *parent_rate)
 {
 	struct clk_fractional_divider *fd = to_clk_fd(hw);
-	unsigned maxn = (fd->nmask >> fd->nshift) + 1;
-	unsigned div;
+	unsigned long m, n;
 
-	if (!rate || rate >= *prate)
-		return *prate;
+	if (!rate || rate >= *parent_rate)
+		return *parent_rate;
 
-	div = gcd(*prate, rate);
-
-	while ((*prate / div) > maxn) {
-		div <<= 1;
-		rate <<= 1;
-	}
+	rational_best_approximation(rate, *parent_rate,
+			fd->mmask >> fd->mshift, fd->nmask >> fd->nshift, &m, &n);
 
-	return rate;
+	return mult_frac(rate, m, n);
 }
 
 static int clk_fd_set_rate(struct clk_hw *hw, unsigned long rate,
@@ -70,13 +63,11 @@ static int clk_fd_set_rate(struct clk_hw *hw, unsigned long rate,
 {
 	struct clk_fractional_divider *fd = to_clk_fd(hw);
 	unsigned long flags = 0;
-	unsigned long div;
-	unsigned n, m;
+	unsigned long n, m;
 	u32 val;
 
-	div = gcd(parent_rate, rate);
-	m = rate / div;
-	n = parent_rate / div;
+	rational_best_approximation(rate, parent_rate,
+			fd->mmask >> fd->mshift, fd->nmask >> fd->nshift, &m, &n);
 
 	if (fd->lock)
 		spin_lock_irqsave(fd->lock, flags);
-- 
2.1.4


  reply	other threads:[~2015-03-30 18:58 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-30 18:57 [PATCH v2 0/2] clk: fractional-divider: do a clean up Andy Shevchenko
2015-03-30 18:57 ` Andy Shevchenko [this message]
2015-03-31  0:32   ` [PATCH v2 1/2] clk: fractional-divider: switch to rational best approximation Stephen Boyd
2015-03-31  7:42     ` Andy Shevchenko
2015-03-31  9:33       ` Andy Shevchenko
2015-03-30 18:57 ` [PATCH v2 2/2] clk: fractional-divider: fix sparse warnings Andy Shevchenko

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=1427741869-239562-2-git-send-email-andriy.shevchenko@linux.intel.com \
    --to=andriy.shevchenko@linux.intel.com \
    --cc=heikki.krogerus@linux.intel.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=sboyd@codeaurora.org \
    --subject='Re: [PATCH v2 1/2] clk: fractional-divider: switch to rational best approximation' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).