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Paul Walmsley de07fedd79 [ARM] OMAP2/3 clock: don't use a barrier after clk_disable() 
clk_disable() previously used an ARM barrier, wmb(), to try to ensure
that the hardware write completed before continuing.  There are some
problems with this approach.

The first problem is that wmb() only ensures that the write leaves the
ARM -- not that it actually reaches the endpoint device.  In this
case, the endpoint device - either the PRM, CM, or SCM - is three
interconnects away from the ARM, and the final interconnect is
low-speed.  And the OCP interconnects will post the write, who knows
how long that will take to complete.  So the wmb() is not really what
we want.

Worse, the wmb() is indiscriminate; it will cause the ARM to flush any
other unrelated buffered writes and wait for the local interconnect to
acknowledge them - potentially very expensive.

This first problem could be fixed by doing a readback of the same PRM/CM/SCM
register.  Since these devices use a single OCP thread, this will cause the
MPU to wait for the write to complete.

But the primary problem is a conceptual one: clk_disable() should not
need any kind of barrier.  clk_enable() needs one since device driver
code must not access a device until its clocks are known to be
enabled.  But clk_disable() has no such restriction.

Since blocking the MPU on a PRM/CM/SCM write can be a very
high-latency operation - several hundred MPU cycles - it's worth
avoiding this barrier if possible.

linux-omap source commit is f4aacad2c0ed1055622d5c1e910befece24ef0e2.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
 		2009-02-08 17:50:42 +00:00
..
boot Merge branch 'for-rmk' of git://git.kernel.org/pub/scm/linux/kernel/git/ycmiao/pxa-linux-2.6 into devel 2008-12-02 22:07:40 +00:00
common [ARM] clkdev: fix clock matching 2009-01-24 11:41:20 +00:00
configs eeprom: More consistent symbol names 2009-01-26 21:19:57 +01:00
include/asm byteorder: make swab.h include asm/swab.h like a regular header 2009-01-14 19:56:50 -08:00
kernel annotate that [fp, #-4] is the saved lr 2009-01-31 01:21:56 +01:00
lib Merge branch 'clps7500' into devel 2008-11-27 12:39:43 +00:00
mach-aaec2000 arm: struct device - replace bus_id with dev_name(), dev_set_name() 2009-01-06 10:44:43 -08:00
mach-at91 [ARM] fix AT91, davinci, h720x, ks8695, msm, mx2, mx3, netx, omap1, omap2, pxa, s3c 2009-01-08 16:29:42 +00:00
mach-clps711x [ARM] clps711x: fix warning in edb7211-mm.c 2009-01-08 16:29:42 +00:00
mach-davinci USB: musb_hdrc: another davinci buildfix (otg related) 2009-01-27 16:15:32 -08:00
mach-ebsa110 [ARM] Hide ISA DMA API when ISA_DMA_API is unset 2008-11-29 18:42:40 +00:00
mach-ep93xx arm: struct device - replace bus_id with dev_name(), dev_set_name() 2009-01-06 10:44:43 -08:00
mach-footbridge Merge branch 'devel' 2009-01-08 22:01:49 +00:00
mach-h720x [ARM] fix AT91, davinci, h720x, ks8695, msm, mx2, mx3, netx, omap1, omap2, pxa, s3c 2009-01-08 16:29:42 +00:00
mach-imx [ARM] i.MX add missing include 2009-01-12 12:14:40 +01:00
mach-integrator libata-sff: fix incorrect EH message 2009-01-26 06:36:16 -05:00
mach-iop13xx [ARM] Hide ISA DMA API when ISA_DMA_API is unset 2008-11-29 18:42:40 +00:00
mach-iop32x [ARM] Hide ISA DMA API when ISA_DMA_API is unset 2008-11-29 18:42:40 +00:00
mach-iop33x [ARM] fix missing includes for iop33x and sa1100_ir 2008-12-01 23:01:19 +00:00
mach-ixp4xx Merge branch 'cpus4096-for-linus-2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2009-01-02 11:44:09 -08:00
mach-ixp23xx [ARM] Hide ISA DMA API when ISA_DMA_API is unset 2008-11-29 18:42:40 +00:00
mach-ixp2000 [ARM] Hide ISA DMA API when ISA_DMA_API is unset 2008-11-29 18:42:40 +00:00
mach-kirkwood [ARM] 5357/1: Kirkwood: add missing ge01 tclk initialization 2009-01-08 16:29:41 +00:00
mach-ks8695 [ARM] fix AT91, davinci, h720x, ks8695, msm, mx2, mx3, netx, omap1, omap2, pxa, s3c 2009-01-08 16:29:42 +00:00
mach-l7200 [ARM] Add a common typesafe __io implementation 2008-11-30 11:45:54 +00:00
mach-lh7a40x arm: struct device - replace bus_id with dev_name(), dev_set_name() 2009-01-06 10:44:43 -08:00
mach-loki [ARM] Hide ISA DMA API when ISA_DMA_API is unset 2008-11-29 18:42:40 +00:00
mach-msm [ARM] msm: fix build errors 2009-01-28 10:19:52 +00:00
mach-mv78xx0 [ARM] 5361/1: mv78xx0: fix compilation error 2009-01-08 16:29:40 +00:00
mach-mx1 [ARM] MXC: remove dependency to other include files from irqs.h 2008-12-18 16:40:11 +01:00
mach-mx2 [ARM] fix AT91, davinci, h720x, ks8695, msm, mx2, mx3, netx, omap1, omap2, pxa, s3c 2009-01-08 16:29:42 +00:00
mach-mx3 [ARM] fix AT91, davinci, h720x, ks8695, msm, mx2, mx3, netx, omap1, omap2, pxa, s3c 2009-01-08 16:29:42 +00:00
mach-netx [ARM] fix netx 2009-01-08 16:29:44 +00:00
mach-ns9xxx Merge branch 'cpus4096-for-linus-2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2009-01-02 11:44:09 -08:00
mach-omap1 [ARM] omap: create a proper tree of clocks 2009-02-08 17:50:42 +00:00
mach-omap2 [ARM] OMAP2/3 clock: don't use a barrier after clk_disable() 2009-02-08 17:50:42 +00:00
mach-orion5x [ARM] 5360/1: Orion: fix compilation error 2009-01-08 16:29:40 +00:00
mach-pnx4008 [ARM] fix pnx4008 2009-01-08 16:29:43 +00:00
mach-pxa Merge git://git.infradead.org/mtd-2.6 2009-01-09 12:37:15 -08:00
mach-realview [ARM] Fix realview build 2009-01-08 16:29:41 +00:00
mach-rpc [ARM] give RiscPC a NR_IRQS definition and remove default 2008-11-29 19:14:31 +00:00
mach-s3c24a0/include/mach [ARM] S3C24A0: Remove duplicate <mach/io.h> file 2008-12-18 16:35:59 +00:00
mach-s3c2400 [ARM] remove a common set of __virt_to_bus definitions 2008-11-28 15:36:49 +00:00
mach-s3c2410 [ARM] fix AT91, davinci, h720x, ks8695, msm, mx2, mx3, netx, omap1, omap2, pxa, s3c 2009-01-08 16:29:42 +00:00
mach-s3c2412 [ARM] S3C: Remove unnecessary <linux/delay.h> includes 2008-12-18 16:36:02 +00:00
mach-s3c2440 [ARM] 5358/1: AT2440EVB: Use new include path of mci.h 2009-01-08 16:29:41 +00:00
mach-s3c2442 [ARM] Arrange for platforms to select appropriate CPU support 2008-11-27 12:38:00 +00:00
mach-s3c2443 [ARM] S3C: Remove unnecessary <linux/delay.h> includes 2008-12-18 16:36:02 +00:00
mach-s3c6400 [ARM] fix AT91, davinci, h720x, ks8695, msm, mx2, mx3, netx, omap1, omap2, pxa, s3c 2009-01-08 16:29:42 +00:00
mach-s3c6410 Merge branch 'next-s3c64xx-device' into next-merged 2008-12-18 16:17:37 +00:00
mach-sa1100 rename platform_driver name "flash" to "sa1100-mtd" 2009-01-31 01:21:58 +01:00
mach-shark [ARM] Rename ISA mach/dma.h header to mach/isa-dma.h 2008-11-29 18:49:55 +00:00
mach-versatile arm: struct device - replace bus_id with dev_name(), dev_set_name() 2009-01-06 10:44:43 -08:00
mach-w90x900 [ARM] w90x900: fix build errors and warnings 2009-01-12 13:51:03 +00:00
mm [ARM] 5366/1: fix shared memory coherency with VIVT L1 + L2 caches 2009-01-28 16:55:00 +00:00
nwfpe [ARM] Convert asm/uaccess.h to linux/uaccess.h 2008-09-06 11:35:55 +01:00
oprofile cpumask: make irq_set_affinity() take a const struct cpumask 2008-12-13 21:20:26 +10:30
plat-iop [ARM] iop: iop3xx needs registers mapped uncached+unbuffered 2008-11-09 11:18:36 +00:00
plat-mxc i.MX31: framebuffer driver 2009-01-21 10:32:34 -07:00
plat-omap [ARM] omap: create a proper tree of clocks 2009-02-08 17:50:42 +00:00
plat-orion Merge branch 'cpus4096-for-linus-2' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip 2009-01-02 11:44:09 -08:00
plat-s3c [ARM] fix AT91, davinci, h720x, ks8695, msm, mx2, mx3, netx, omap1, omap2, pxa, s3c 2009-01-08 16:29:42 +00:00
plat-s3c24xx [ARM] fix AT91, davinci, h720x, ks8695, msm, mx2, mx3, netx, omap1, omap2, pxa, s3c 2009-01-08 16:29:42 +00:00
plat-s3c64xx [ARM] S3C64XX: Fix EINT group macro definition 2009-01-08 16:25:24 +00:00
tools [ARM] Update mach-types 2008-11-30 16:39:42 +00:00
vfp [ARM] 5349/1: VFP: Add PM code to save and restore current VFP state 2008-12-18 21:21:34 +00:00
Kconfig Staging: Kconfig for ARCH=arm,8300, cris 2009-01-06 13:51:38 -08:00
Kconfig-nommu [ARM] 4532/1: allow configuration of processor ID 2007-10-12 23:43:02 +01:00
Kconfig.debug [ARM] CONFIG_DEBUG_STACK_USAGE 2008-01-26 14:50:06 +00:00
Makefile Merge branch 'next-merged' of git://aeryn.fluff.org.uk/bjdooks/linux into devel 2008-12-18 22:15:30 +00:00