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ARM: OMAP4: clock: Lock PLLs in the right sequence
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On OMAP4 we have clk_set_rate()s being done for a few
DPLL clock nodes, as part of the clock init code, since
the bootloaders no longer locks these DPLLs.

So we have a clk_set_rate() done for a ABE DPLL node (which
inturn locks it) followed by a clk_set_rate() for the USB DPLL.

With USB DPLL being in bypass, we have this parent->child
relationship thats formed while the clocks get registered.

dpll_abe_ck
    |
    V
dpll_abe_x2_ck
    |
    V
dpll_abe_m3x2_ck
    |
    V
usb_hs_clk_div_ck
    |
    V
dpll_usb_ck

This is because usb_hs_clk_div_ck is bypass clock for dpll_usb_ck.

So with this parent->child relationship in place, a clk_set_rate()
on ABE DPLL results eventually in a clk_set_rate() call on USB DPLL,
because CCF does a clk_change_rate() (as part of clk_set_rate()) on
all downstream clocks resulting from a rate change on the top clock.

So its important that we lock USB DPLL before we lock ABE DPLL.
Without which we see these error logs at boot.
[These error logs will not be seen if using a bootloader that locks
USB DPLL]

[    0.000000] clock: dpll_usb_ck failed transition to 'locked'
[    0.000000] Division by zero in kernel.
[    0.000000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.10.0-03445-gfb2af00-dirty #7
[    0.000000] [<c001bfe8>] (unwind_backtrace+0x0/0xf4) from [<c001868c>] (show_stack+0x10/0x14)
[    0.000000] [<c001868c>] (show_stack+0x10/0x14) from [<c02deb28>] (Ldiv0+0x8/0x10)
[    0.000000] [<c02deb28>] (Ldiv0+0x8/0x10) from [<c0477030>] (clk_divider_set_rate+0x10/0x114)
[    0.000000] [<c0477030>] (clk_divider_set_rate+0x10/0x114) from [<c0476ef4>] (clk_change_rate+0x38/0xb8)
[    0.000000] [<c0476ef4>] (clk_change_rate+0x38/0xb8) from [<c0476f5c>] (clk_change_rate+0xa0/0xb8)
[    0.000000] Division by zero in kernel.
[    0.000000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.10.0-03445-gfb2af00-dirty #7
[    0.000000] [<c001bfe8>] (unwind_backtrace+0x0/0xf4) from [<c001868c>] (show_stack+0x10/0x14)
[    0.000000] [<c001868c>] (show_stack+0x10/0x14) from [<c02deb28>] (Ldiv0+0x8/0x10)
[    0.000000] [<c02deb28>] (Ldiv0+0x8/0x10) from [<c0477030>] (clk_divider_set_rate+0x10/0x114)
[    0.000000] [<c0477030>] (clk_divider_set_rate+0x10/0x114) from [<c0476ef4>] (clk_change_rate+0x38/0xb8)
[    0.000000] [<c0476ef4>] (clk_change_rate+0x38/0xb8) from [<c0476f5c>] (clk_change_rate+0xa0/0xb8)
[    0.000000] Division by zero in kernel.
[    0.000000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.10.0-03445-gfb2af00-dirty #7
[    0.000000] [<c001bfe8>] (unwind_backtrace+0x0/0xf4) from [<c001868c>] (show_stack+0x10/0x14)
[    0.000000] [<c001868c>] (show_stack+0x10/0x14) from [<c02deb28>] (Ldiv0+0x8/0x10)
[    0.000000] [<c02deb28>] (Ldiv0+0x8/0x10) from [<c0477030>] (clk_divider_set_rate+0x10/0x114)
[    0.000000] [<c0477030>] (clk_divider_set_rate+0x10/0x114) from [<c0476ef4>] (clk_change_rate+0x38/0xb8)
[    0.000000] [<c0476ef4>] (clk_change_rate+0x38/0xb8) from [<c0476f5c>] (clk_change_rate+0xa0/0xb8)
[    0.000000] Division by zero in kernel.
[    0.000000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.10.0-03445-gfb2af00-dirty #7
[    0.000000] [<c001bfe8>] (unwind_backtrace+0x0/0xf4) from [<c001868c>] (show_stack+0x10/0x14)
[    0.000000] [<c001868c>] (show_stack+0x10/0x14) from [<c02deb28>] (Ldiv0+0x8/0x10)
[    0.000000] [<c02deb28>] (Ldiv0+0x8/0x10) from [<c0477030>] (clk_divider_set_rate+0x10/0x114)
[    0.000000] [<c0477030>] (clk_divider_set_rate+0x10/0x114) from [<c0476ef4>] (clk_change_rate+0x38/0xb8)
[    0.000000] [<c0476ef4>] (clk_change_rate+0x38/0xb8) from [<c0476f5c>] (clk_change_rate+0xa0/0xb8)
[    0.000000] Division by zero in kernel.
[    0.000000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.10.0-03445-gfb2af00-dirty #7
[    0.000000] [<c001bfe8>] (unwind_backtrace+0x0/0xf4) from [<c001868c>] (show_stack+0x10/0x14)
[    0.000000] [<c001868c>] (show_stack+0x10/0x14) from [<c02deb28>] (Ldiv0+0x8/0x10)
[    0.000000] [<c02deb28>] (Ldiv0+0x8/0x10) from [<c0477030>] (clk_divider_set_rate+0x10/0x114)
[    0.000000] [<c0477030>] (clk_divider_set_rate+0x10/0x114) from [<c0476ef4>] (clk_change_rate+0x38/0xb8)
[    0.000000] [<c0476ef4>] (clk_change_rate+0x38/0xb8) from [<c0476f5c>] (clk_change_rate+0xa0/0xb8)
[    0.000000] Division by zero in kernel.
[    0.000000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.10.0-03445-gfb2af00-dirty #7
[    0.000000] [<c001bfe8>] (unwind_backtrace+0x0/0xf4) from [<c001868c>] (show_stack+0x10/0x14)
[    0.000000] [<c001868c>] (show_stack+0x10/0x14) from [<c02deb28>] (Ldiv0+0x8/0x10)
[    0.000000] [<c02deb28>] (Ldiv0+0x8/0x10) from [<c0477030>] (clk_divider_set_rate+0x10/0x114)
[    0.000000] [<c0477030>] (clk_divider_set_rate+0x10/0x114) from [<c0476ef4>] (clk_change_rate+0x38/0xb8)
[    0.000000] [<c0476ef4>] (clk_change_rate+0x38/0xb8) from [<c0476f5c>] (clk_change_rate+0xa0/0xb8)
[    0.000000] clock: trace_clk_div_ck: could not find divisor for target rate 0 for parent pmd_trace_clk_mux_ck
[    0.000000] Division by zero in kernel.

Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>
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Rajendra Nayak authored and Paul Walmsley committed Aug 23, 2013
1 parent b36f4be commit eeb6603
Showing 1 changed file with 12 additions and 8 deletions.
20 changes: 12 additions & 8 deletions arch/arm/mach-omap2/cclock44xx_data.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -1706,6 +1706,18 @@ int __init omap4xxx_clk_init(void)

omap2_clk_disable_autoidle_all();

/*
* A set rate of ABE DPLL inturn triggers a set rate of USB DPLL
* when its in bypass. So always lock USB before ABE DPLL.
*/
/*
* Lock USB DPLL on OMAP4 devices so that the L3INIT power
* domain can transition to retention state when not in use.
*/
rc = clk_set_rate(&dpll_usb_ck, OMAP4_DPLL_USB_DEFFREQ);
if (rc)
pr_err("%s: failed to configure USB DPLL!\n", __func__);

/*
* On OMAP4460 the ABE DPLL fails to turn on if in idle low-power
* state when turning the ABE clock domain. Workaround this by
Expand All @@ -1718,13 +1730,5 @@ int __init omap4xxx_clk_init(void)
if (rc)
pr_err("%s: failed to configure ABE DPLL!\n", __func__);

/*
* Lock USB DPLL on OMAP4 devices so that the L3INIT power
* domain can transition to retention state when not in use.
*/
rc = clk_set_rate(&dpll_usb_ck, OMAP4_DPLL_USB_DEFFREQ);
if (rc)
pr_err("%s: failed to configure USB DPLL!\n", __func__);

return 0;
}

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