linux-kernel - [PATCH v3] clk: mediatek: Allow changing PLL rate when it is off

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Date:   Fri, 4 Nov 2016 14:42:56 +0800
From:   James Liao <jamesjj.liao@...iatek.com>
To:     Matthias Brugger <matthias.bgg@...il.com>,
        Mike Turquette <mturquette@...aro.org>,
        Stephen Boyd <sboyd@...eaurora.org>
CC:     <srv_heupstream@...iatek.com>, Daniel Kurtz <djkurtz@...omium.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-mediatek@...ts.infradead.org>,
        James Liao <jamesjj.liao@...iatek.com>
Subject: [PATCH v3] clk: mediatek: Allow changing PLL rate when it is off

Some modules may need to change its clock rate before turn on it.
So changing PLL's rate when it is off should be allowed.
This patch removes PLL enabled check before set rate, so that
PLLs can set new frequency even if they are off.

On MT8173 for example, ARMPLL's enable bit can be controlled by
other HW. That means ARMPLL may be turned on even if we (CPU / SW)
set ARMPLL's enable bit as 0. In this case, SW may want and can
still change ARMPLL's rate by changing its pcw and postdiv settings.
But without this patch, new pcw setting will not be applied because
its enable bit is 0.

Signed-off-by: James Liao <jamesjj.liao@...iatek.com>
Acked-by: Michael Turquette <mturuqette@...libre.com>
---
Please refer to previous comments in [1] and [2].

changes since v2:
- Rebase to v4.9-rc1.

changes since v1:
- Add more explanation in commit messages.

[1] https://patchwork.kernel.org/patch/7983221/
[2] https://patchwork.kernel.org/patch/7998891/

 drivers/clk/mediatek/clk-pll.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/clk/mediatek/clk-pll.c b/drivers/clk/mediatek/clk-pll.c
index 0c2deac..80f57b4 100644
--- a/drivers/clk/mediatek/clk-pll.c
+++ b/drivers/clk/mediatek/clk-pll.c
@@ -91,9 +91,6 @@ static void mtk_pll_set_rate_regs(struct mtk_clk_pll *pll, u32 pcw,
 		int postdiv)
 {
 	u32 con1, val;
-	int pll_en;
-
-	pll_en = readl(pll->base_addr + REG_CON0) & CON0_BASE_EN;
 
 	/* set postdiv */
 	val = readl(pll->pd_addr);
@@ -114,15 +111,13 @@ static void mtk_pll_set_rate_regs(struct mtk_clk_pll *pll, u32 pcw,
 
 	con1 = readl(pll->base_addr + REG_CON1);
 
-	if (pll_en)
-		con1 |= CON0_PCW_CHG;
+	con1 |= CON0_PCW_CHG;
 
 	writel(con1, pll->base_addr + REG_CON1);
 	if (pll->tuner_addr)
 		writel(con1 + 1, pll->tuner_addr);
 
-	if (pll_en)
-		udelay(20);
+	udelay(20);
 }
 
 /*
-- 
1.9.1