linux-kernel - [PATCH 5.16 0052/1017] clk: rockchip: re-add rational best approximation algorithm to the fractional divider

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Date:   Tue,  5 Apr 2022 09:16:05 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Quentin Schulz <foss+kernel@...il.net>,
        Quentin Schulz <quentin.schulz@...obroma-systems.com>,
        Heiko Stuebner <heiko@...ech.de>
Subject: [PATCH 5.16 0052/1017] clk: rockchip: re-add rational best approximation algorithm to the fractional divider

From: Quentin Schulz <quentin.schulz@...obroma-systems.com>

commit 10b74af310735860510a533433b1d3ab2e05a138 upstream.

In commit 4e7cf74fa3b2 ("clk: fractional-divider: Export approximation
algorithm to the CCF users"), the code handling the rational best
approximation algorithm was replaced by a call to the core
clk_fractional_divider_general_approximation function which did the same
thing back then.

However, in commit 82f53f9ee577 ("clk: fractional-divider: Introduce
POWER_OF_TWO_PS flag"), this common code was made conditional on
CLK_FRAC_DIVIDER_POWER_OF_TWO_PS flag which was not added back to the
rockchip clock driver.

This broke the ltk050h3146w-a2 MIPI DSI display present on a PX30-based
downstream board.

Let's add the flag to the fractional divider flags so that the original
and intended behavior is brought back to the rockchip clock drivers.

Fixes: 82f53f9ee577 ("clk: fractional-divider: Introduce POWER_OF_TWO_PS flag")
Cc: stable@...r.kernel.org
Cc: Quentin Schulz <foss+kernel@...il.net>
Signed-off-by: Quentin Schulz <quentin.schulz@...obroma-systems.com>
Link: https://lore.kernel.org/r/20220131163224.708002-1-quentin.schulz@theobroma-systems.com
Signed-off-by: Heiko Stuebner <heiko@...ech.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/clk/rockchip/clk.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/drivers/clk/rockchip/clk.c
+++ b/drivers/clk/rockchip/clk.c
@@ -180,6 +180,7 @@ static void rockchip_fractional_approxim
 		unsigned long rate, unsigned long *parent_rate,
 		unsigned long *m, unsigned long *n)
 {
+	struct clk_fractional_divider *fd = to_clk_fd(hw);
 	unsigned long p_rate, p_parent_rate;
 	struct clk_hw *p_parent;

@@ -190,6 +191,8 @@ static void rockchip_fractional_approxim
 		*parent_rate = p_parent_rate;
 	}

+	fd->flags |= CLK_FRAC_DIVIDER_POWER_OF_TWO_PS;
+
 	clk_fractional_divider_general_approximation(hw, rate, parent_rate, m, n);
 }