[PATCH V2 RESEND] clk: mxs: Fix invalid 32-bit access to frac registers

Stefan Wahren
2015-01-30T19:15:28Z

According to i.MX23 and i.MX28 reference manual [1],[2] the fractional
clock control register is 32-bit wide, but is separated in 4 parts.
So write instructions must not apply to more than 1 part at once.

The clk init for the i.MX28 violates this restriction and all the other
accesses on that register suggest that there isn't such a restriction.

This patch restricts the access to this register to byte instructions and
extends the comment in the init functions.

Btw the imx23 init now uses a R-M-W sequence just like imx28 init
to avoid any clock glitches.

The changes has been tested with a i.MX23 and a i.MX28 board.

[1] - http://cache.freescale.com/files/dsp/doc/ref_manual/IMX23RM.pdf
[2] - http://cache.freescale.com/files/dsp/doc/ref_manual/MCIMX28RM.pdf

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Marek Vasut <marex@denx.de>
---

Changes in V2:
- use relaxed access operations in clk-ref

drivers/clk/mxs/clk-imx23.c | 11 ++++++++---
drivers/clk/mxs/clk-imx28.c | 19 +++++++++++++------
drivers/clk/mxs/clk-ref.c | 19 ++++++++++---------
3 files changed, 31 insertions(+), 18 deletions(-)

diff --git a/drivers/clk/mxs/clk-imx23.c b/drivers/clk/mxs/clk-imx23.c
index 9fc9359..a084566 100644
--- a/drivers/clk/mxs/clk-imx23.c
+++ b/drivers/clk/mxs/clk-imx23.c
@@ -46,11 +46,13 @@ static void __iomem *digctrl;
#define BP_CLKSEQ_BYPASS_SAIF 0
#define BP_CLKSEQ_BYPASS_SSP 5
#define BP_SAIF_DIV_FRAC_EN 16
-#define BP_FRAC_IOFRAC 24
+
+#define FRAC_IO 3

static void __init clk_misc_init(void)
{
u32 val;
+ u8 frac;

/* Gate off cpu clock in WFI for power saving */
writel_relaxed(1 << BP_CPU_INTERRUPT_WAIT, CPU + SET);
@@ -72,9 +74,12 @@ static void __init clk_misc_init(void)
/*
* 480 MHz seems too high to be ssp clock source directly,
* so set frac to get a 288 MHz ref_io.
+ * According to reference manual we must access frac bytewise.
*/
- writel_relaxed(0x3f << BP_FRAC_IOFRAC, FRAC + CLR);
- writel_relaxed(30 << BP_FRAC_IOFRAC, FRAC + SET);
+ frac = readb_relaxed(FRAC + FRAC_IO);
+ frac &= ~0x3f;
+ frac |= 30;
+ writeb_relaxed(frac, FRAC + FRAC_IO);
}

static const char *sel_pll[] __initconst = { "pll", "ref_xtal", };
diff --git a/drivers/clk/mxs/clk-imx28.c b/drivers/clk/mxs/clk-imx28.c
index a6c3501..c541377 100644
--- a/drivers/clk/mxs/clk-imx28.c
+++ b/drivers/clk/mxs/clk-imx28.c
@@ -53,8 +53,9 @@ static void __iomem *clkctrl;
#define BP_ENET_SLEEP 31
#define BP_CLKSEQ_BYPASS_SAIF0 0
#define BP_CLKSEQ_BYPASS_SSP0 3
-#define BP_FRAC0_IO1FRAC 16
-#define BP_FRAC0_IO0FRAC 24
+
+#define FRAC0_IO1 2
+#define FRAC0_IO0 3

static void __iomem *digctrl;
#define DIGCTRL digctrl
@@ -85,6 +86,7 @@ int mxs_saif_clkmux_select(unsigned int clkmux)
static void __init clk_misc_init(void)
{
u32 val;
+ u8 frac;

/* Gate off cpu clock in WFI for power saving */
writel_relaxed(1 << BP_CPU_INTERRUPT_WAIT, CPU + SET);
@@ -118,11 +120,16 @@ static void __init clk_misc_init(void)
/*
* 480 MHz seems too high to be ssp clock source directly,
* so set frac0 to get a 288 MHz ref_io0 and ref_io1.
+ * According to reference manual we must access frac0 bytewise.
*/
- val = readl_relaxed(FRAC0);
- val &= ~((0x3f << BP_FRAC0_IO0FRAC) | (0x3f << BP_FRAC0_IO1FRAC));
- val |= (30 << BP_FRAC0_IO0FRAC) | (30 << BP_FRAC0_IO1FRAC);
- writel_relaxed(val, FRAC0);
+ frac = readb_relaxed(FRAC0 + FRAC0_IO0);
+ frac &= ~0x3f;
+ frac |= 30;
+ writeb_relaxed(frac, FRAC0 + FRAC0_IO0);
+ frac = readb_relaxed(FRAC0 + FRAC0_IO1);
+ frac &= ~0x3f;
+ frac |= 30;
+ writeb_relaxed(frac, FRAC0 + FRAC0_IO1);
}

static const char *sel_cpu[] __initconst = { "ref_cpu", "ref_xtal", };
diff --git a/drivers/clk/mxs/clk-ref.c b/drivers/clk/mxs/clk-ref.c
index 4adeed6..ad3851c 100644
--- a/drivers/clk/mxs/clk-ref.c
+++ b/drivers/clk/mxs/clk-ref.c
@@ -16,6 +16,8 @@
#include <linux/slab.h>
#include "clk.h"

+#define BF_CLKGATE BIT(7)
+
/**
* struct clk_ref - mxs reference clock
* @hw: clk_hw for the reference clock
@@ -39,7 +41,7 @@ static int clk_ref_enable(struct clk_hw *hw)
{
struct clk_ref *ref = to_clk_ref(hw);

- writel_relaxed(1 << ((ref->idx + 1) * 8 - 1), ref->reg + CLR);
+ writeb_relaxed(BF_CLKGATE, ref->reg + ref->idx + CLR);

return 0;
}
@@ -48,7 +50,7 @@ static void clk_ref_disable(struct clk_hw *hw)
{
struct clk_ref *ref = to_clk_ref(hw);

- writel_relaxed(1 << ((ref->idx + 1) * 8 - 1), ref->reg + SET);
+ writeb_relaxed(BF_CLKGATE, ref->reg + ref->idx + SET);
}

static unsigned long clk_ref_recalc_rate(struct clk_hw *hw,
@@ -56,7 +58,7 @@ static unsigned long clk_ref_recalc_rate(struct clk_hw *hw,
{
struct clk_ref *ref = to_clk_ref(hw);
u64 tmp = parent_rate;
- u8 frac = (readl_relaxed(ref->reg) >> (ref->idx * 8)) & 0x3f;
+ u8 frac = readb_relaxed(ref->reg + ref->idx) & 0x3f;

tmp *= 18;
do_div(tmp, frac);
@@ -93,8 +95,7 @@ static int clk_ref_set_rate(struct clk_hw *hw, unsigned long rate,
struct clk_ref *ref = to_clk_ref(hw);
unsigned long flags;
u64 tmp = parent_rate;
- u32 val;
- u8 frac, shift = ref->idx * 8;
+ u8 frac, val;

tmp = tmp * 18 + rate / 2;
do_div(tmp, rate);
@@ -107,10 +108,10 @@ static int clk_ref_set_rate(struct clk_hw *hw, unsigned long rate,

spin_lock_irqsave(&mxs_lock, flags);

- val = readl_relaxed(ref->reg);
- val &= ~(0x3f << shift);
- val |= frac << shift;
- writel_relaxed(val, ref->reg);
+ val = readb_relaxed(ref->reg + ref->idx);
+ val &= ~0x3f;
+ val |= frac;
+ writeb_relaxed(val, ref->reg + ref->idx);

spin_unlock_irqrestore(&mxs_lock, flags);

--
1.7.9.5