2019-06-04 08:11:33 +00:00
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/* SPDX-License-Identifier: GPL-2.0-only */
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2012-04-19 16:53:13 +00:00
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/*
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* arch/arm/mach-spear13XX/headsmp.S
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*
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* Picked from realview
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* Copyright (c) 2012 ST Microelectronics Limited
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2014-04-18 22:07:16 +00:00
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* Shiraz Hashim <shiraz.linux.kernel@gmail.com>
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2012-04-19 16:53:13 +00:00
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*/
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#include <linux/linkage.h>
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#include <linux/init.h>
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__INIT
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/*
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* spear13xx specific entry point for secondary CPUs. This provides
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* a "holding pen" into which all secondary cores are held until we're
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* ready for them to initialise.
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*/
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ENTRY(spear13xx_secondary_startup)
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mrc p15, 0, r0, c0, c0, 5
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and r0, r0, #15
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adr r4, 1f
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ldmia r4, {r5, r6}
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sub r4, r4, r5
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add r6, r6, r4
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pen: ldr r7, [r6]
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cmp r7, r0
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bne pen
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/* re-enable coherency */
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mrc p15, 0, r0, c1, c0, 1
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orr r0, r0, #(1 << 6) | (1 << 0)
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mcr p15, 0, r0, c1, c0, 1
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/*
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* we've been released from the holding pen: secondary_stack
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* should now contain the SVC stack for this core
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*/
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b secondary_startup
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.align
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1: .long .
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ARM: smp: remove arch-provided "pen_release"
Consolidating the "pen_release" stuff amongst the various SoC
implementations gives credence to having a CPU holding pen for
secondary CPUs. However, this is far from the truth.
Many SoC implementations cargo-cult copied various bits of the pen
release implementation from the initial Realview/Versatile Express
implementation without understanding what it was or why it existed.
The reason it existed is because these are _development_ platforms,
and some board firmware is unable to individually control the
startup of secondary CPUs. Moreover, they do not have a way to
power down or reset secondary CPUs for hot-unplug. Hence, the
pen_release implementation was designed for ARM Ltd's development
platforms to provide a working implementation, even though it is
very far from what is required.
It was decided a while back to reduce the duplication by consolidating
the "pen_release" variable, but this only made the situation worse -
we have ended up with several implementations that read this variable
but do not write it - again, showing the cargo-cult mentality at work,
lack of proper review of new code, and in some cases a lack of testing.
While it would be preferable to remove pen_release entirely from the
kernel, this is not possible without help from the SoC maintainers,
which seems to be lacking. However, I want to remove pen_release from
arch code to remove the credence that having it gives.
This patch removes pen_release from the arch code entirely, adding
private per-SoC definitions for it instead, and explicitly stating
that write_pen_release() is cargo-cult copied and should not be
copied any further. Rename write_pen_release() in a similar fashion
as well.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
2018-12-13 14:02:48 +00:00
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.long spear_pen_release
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2012-04-19 16:53:13 +00:00
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ENDPROC(spear13xx_secondary_startup)
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