linux-kernel - [PATCH v1 2/3] clk: fractional-divider: Introduce NO

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Message-Id: <20210715120752.29174-2-andriy.shevchenko@linux.intel.com>
Date:   Thu, 15 Jul 2021 15:07:51 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Heiko Stuebner <heiko@...ech.de>,
        Elaine Zhang <zhangqing@...k-chips.com>,
        Stephen Boyd <sboyd@...nel.org>, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org
Cc:     Michael Turquette <mturquette@...libre.com>,
        Liu Ying <victor.liu@....com>
Subject: [PATCH v1 2/3] clk: fractional-divider: Introduce NO_PRESCALER flag

The newly introduced flag, when set, makes the flow to skip
the assumption that the caller will use an additional 2^scale
prescaler to get the desired clock rate.

Reported-by: Liu Ying <victor.liu@....com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
---
 drivers/clk/clk-fractional-divider.c | 2 +-
 include/linux/clk-provider.h         | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk-fractional-divider.c
index 535d299af646..b2f9aae9f172 100644
--- a/drivers/clk/clk-fractional-divider.c
+++ b/drivers/clk/clk-fractional-divider.c
@@ -84,7 +84,7 @@ void clk_fractional_divider_general_approximation(struct clk_hw *hw,
 	 * by (scale - fd->nwidth) bits.
 	 */
 	scale = fls_long(*parent_rate / rate - 1);
-	if (scale > fd->nwidth)
+	if (scale > fd->nwidth && !(fd->flags & CLK_FRAC_DIVIDER_NO_PRESCALER))
 		rate <<= scale - fd->nwidth;
 
 	rational_best_approximation(rate, *parent_rate,
diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index d83b829305c0..f74d0afe275f 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -1001,6 +1001,10 @@ struct clk_hw *devm_clk_hw_register_fixed_factor(struct device *dev,
  * CLK_FRAC_DIVIDER_BIG_ENDIAN - By default little endian register accesses are
  *	used for the divider register.  Setting this flag makes the register
  *	accesses big endian.
+ * CLK_FRAC_DIVIDER_NO_PRESCALER - By default the resulting rate may be shifted
+ *	left by a few bits in case when the asked one is quite small to satisfy
+ *	the desired range of denominator. If the caller wants to get the best
+ *	rate without using an additional prescaler, this flag may be set.
  */
 struct clk_fractional_divider {
 	struct clk_hw	hw;
@@ -1022,6 +1026,7 @@ struct clk_fractional_divider {
 
 #define CLK_FRAC_DIVIDER_ZERO_BASED		BIT(0)
 #define CLK_FRAC_DIVIDER_BIG_ENDIAN		BIT(1)
+#define CLK_FRAC_DIVIDER_NO_PRESCALER		BIT(2)
 
 extern const struct clk_ops clk_fractional_divider_ops;
 struct clk *clk_register_fractional_divider(struct device *dev,
-- 
2.30.2