This patch fixes a hierarchical-RCU performance bug located by Anton
Blanchard. The problem stems from a misguided attempt to provide a
work-around for jiffies-counter failure. This work-around uses a per-CPU
n_rcu_pending counter, which is incremented on each call to rcu_pending(),
which in turn is called from each scheduling-clock interrupt. Each CPU
then treats this counter as a surrogate for the jiffies counter, so
that if the jiffies counter fails to advance, the per-CPU n_rcu_pending
counter will cause RCU to invoke force_quiescent_state(), which in turn
will (among other things) send resched IPIs to CPUs that have thus far
failed to pass through an RCU quiescent state.
Unfortunately, each CPU resets only its own counter after sending a
batch of IPIs. This means that the other CPUs will also (needlessly)
send -another- round of IPIs, for a full N-squared set of IPIs in the
worst case every three scheduler-clock ticks until the grace period
finally ends. It is not reasonable for a given CPU to reset each and
every n_rcu_pending for all the other CPUs, so this patch instead simply
disables the jiffies-counter "training wheels", thus eliminating the
excessive IPIs.
Note that the jiffies-counter IPIs do not have this problem due to
the fact that the jiffies counter is global, so that the CPU sending
the IPIs can easily reset things, thus preventing the other CPUs from
sending redundant IPIs.
Note also that the n_rcu_pending counter remains, as it will continue to
be used for tracing. It may also see use to update the jiffies counter,
should an appropriate kick-the-jiffies-counter API appear.
Located-by: Anton Blanchard <anton@au1.ibm.com>
Tested-by: Anton Blanchard <anton@au1.ibm.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: anton@samba.org
Cc: akpm@linux-foundation.org
Cc: dipankar@in.ibm.com
Cc: manfred@colorfullife.com
Cc: cl@linux-foundation.org
Cc: josht@linux.vnet.ibm.com
Cc: schamp@sgi.com
Cc: niv@us.ibm.com
Cc: dvhltc@us.ibm.com
Cc: ego@in.ibm.com
Cc: laijs@cn.fujitsu.com
Cc: rostedt@goodmis.org
Cc: peterz@infradead.org
Cc: penberg@cs.helsinki.fi
Cc: andi@firstfloor.org
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
LKML-Reference: <12396834793575-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Impact: build fix for Sparc and s390
Stephen Rothwell reported that the Sparc build broke:
In file included from kernel/panic.c:12:
include/linux/debug_locks.h: In function '__debug_locks_off':
include/linux/debug_locks.h:15: error: implicit declaration of function 'xchg'
due to:
9eeba61: lockdep: warn about lockdep disabling after kernel taint
There is some inconsistency between architectures about where exactly
xchg() is defined.
The traditional place is in system.h but the more logical point for it
is in atomic.h - where most architectures (especially new ones) have
it defined. These architecture also still offer it via system.h.
Some, such as Sparc or s390 only have it in asm/system.h and not available
via asm/atomic.h at all.
Use the widest set of headers in debug_locks.h and also include asm/system.h.
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <20090414144317.026498df.sfr@canb.auug.org.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/security-testing-2.6:
tomoyo: version bump to 2.2.0.
tomoyo: add Documentation/tomoyo.txt
We ended up incorrectly using '&cur' instead of '&readin' in the
work_on_cpu() -> smp_call_function_single() transformation in commit
01599fca67 ("cpufreq: use
smp_call_function_[single|many]() in acpi-cpufreq.c").
Andrew explains:
"OK, the acpi tree went and had conflicting changes merged into it after
I'd written the patch and it appears that I incorrectly reverted part
of 18b2646fe3 while fixing the resulting
rejects.
Switching it to `readin' looks correct."
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* 'for-rc1/xen/core' of git://git.kernel.org/pub/scm/linux/kernel/git/jeremy/xen:
xen: add FIX_TEXT_POKE to fixmap
xen: honour VCPU availability on boot
xen: clean up gate trap/interrupt constants
xen: set _PAGE_NX in __supported_pte_mask before pagetable construction
xen: resume interrupts before system devices.
xen/mmu: weaken flush_tlb_other test
xen/mmu: some early pagetable cleanups
Xen: Add virt_to_pfn helper function
x86-64: remove PGE from must-have feature list
xen: mask XSAVE from cpuid
NULL noise: arch/x86/xen/smp.c
xen: remove xen_load_gdt debug
xen: make xen_load_gdt simpler
xen: clean up xen_load_gdt
xen: split construction of p2m mfn tables from registration
xen: separate p2m allocation from setting
xen: disable preempt for leave_lazy_mmu
The edac-core driver includes code which assumes that the work_struct
which is included in every delayed_work is the first member of that
structure. This is currently the case but might change in the future, so
use to_delayed_work() instead, which doesn't make such an assumption.
linux-2.6.30-rc1 has the to_delayed_work() function that will allow this
patch to work
Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Doug Thompson <dougthompson@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Fix the edac local pci_write_bits32 to properly note the 'escape' mask if
all ones in a 32-bit word.
Currently no consumer of this function uses that mask, so there is no
danger to existing code.
Signed-off-by: Jeff Haran <jharan@Brocade.COM>
Signed-off-by: Doug Thompson <dougthompson@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Introduce xpc_arch_ops and eliminate numerous individual global definitions.
Signed-off-by: Robin Holt <holt@sgi.com>
Cc: Dean Nelson <dcn@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
sgi-xpc has a window of failure where an open message can be sent and a
subsequent data message can get lost. We have added a new message
(opencomplete) which closes that window.
Signed-off-by: Robin Holt <holt@sgi.com>
Signed-off-by: Dean Nelson <dcn@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The heartbeat timeout functionality in sgi-xpc is currently not trained to
the connection time. If a connection is made and the code is in the last
polling window prior to doing a timeout, the next polling window will see
the heartbeat as unchanged and initiate a no-heartbeat disconnect.
Signed-off-by: Robin Holt <holt@sgi.com>
Signed-off-by: Dean Nelson <dcn@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Dean has moved on to other work. His responsibilities for XP/XPC/XPNET
have been handed to me.
Signed-off-by: Robin Holt <holt@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Use the default mountpoint of debugfs in the pktcdvd ABI.
Signed-off-by: Shen Feng <shen@cn.fujitsu.com>
Cc: <balagi@justmail.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The description about various statistics from memory.stat is not accurate
and confusing at times.
Correct this along with a few other minor cleanups.
Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This is the second go through of the old DMA_nBIT_MASK macro,and there're not
so many of them left,so I put them into one patch.I hope this is the last round.
After this the definition of the old DMA_nBIT_MASK macro could be removed.
Signed-off-by: Yang Hongyang <yanghy@cn.fujitsu.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Tony Lindgren <tony@atomide.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Greg KH <greg@kroah.com>
Cc: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
If two writers allocating blocks to file race with each other (e.g.
because writepages races with ordinary write or two writepages race with
each other), ext2_getblock() can be called on the same inode in parallel.
Before we are going to allocate new blocks, we have to recheck the block
chain we have obtained so far without holding truncate_mutex. Otherwise
we could overwrite the indirect block pointer set by the other writer
leading to data loss.
The below test program by Ying is able to reproduce the data loss with ext2
on in BRD in a few minutes if the machine is under memory pressure:
long kMemSize = 50 << 20;
int kPageSize = 4096;
int main(int argc, char **argv) {
int status;
int count = 0;
int i;
char *fname = "/mnt/test.mmap";
char *mem;
unlink(fname);
int fd = open(fname, O_CREAT | O_EXCL | O_RDWR, 0600);
status = ftruncate(fd, kMemSize);
mem = mmap(0, kMemSize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
// Fill the memory with 1s.
memset(mem, 1, kMemSize);
sleep(2);
for (i = 0; i < kMemSize; i++) {
int byte_good = mem[i] != 0;
if (!byte_good && ((i % kPageSize) == 0)) {
//printf("%d ", i / kPageSize);
count++;
}
}
munmap(mem, kMemSize);
close(fd);
unlink(fname);
if (count > 0) {
printf("Running %d bad page\n", count);
return 1;
}
return 0;
}
Cc: Ying Han <yinghan@google.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Jan Kara <jack@suse.cz>
Cc: Mingming Cao <cmm@us.ibm.com>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
SHMEM_MAX_BYTES was derived from the maximum size of its triple-indirect
swap vector, forgetting to take the MAX_LFS_FILESIZE limit into account.
Never mind 256kB pages, even 8kB pages on 32-bit kernels allowed files to
grow slightly bigger than that supposed maximum.
Fix this by using the min of both (at build time not run time). And it
happens that this calculation is good as far as 8MB pages on 32-bit or
16MB pages on 64-bit: though SHMSWP_MAX_INDEX gets truncated before that,
it's truncated to such large numbers that we don't need to care.
[akpm@linux-foundation.org: it needs pagemap.h]
[akpm@linux-foundation.org: fix sparc64 min() warnings]
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Yuri Tikhonov <yur@emcraft.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Fix a division by zero which we have in shmem_truncate_range() and
shmem_unuse_inode() when using big PAGE_SIZE values (e.g. 256kB on
ppc44x).
With 256kB PAGE_SIZE, the ENTRIES_PER_PAGEPAGE constant becomes too large
(0x1.0000.0000) on a 32-bit kernel, so this patch just changes its type
from 'unsigned long' to 'unsigned long long'.
Hugh: reverted its unsigned long longs in shmem_truncate_range() and
shmem_getpage(): the pagecache index cannot be more than an unsigned long,
so the divisions by zero occurred in unreached code. It's a pity we need
any ULL arithmetic here, but I found no pretty way to avoid it.
Signed-off-by: Yuri Tikhonov <yur@emcraft.com>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Support the Intel 854 Chipset in fbdev.
We test and use the patch on a Thomson IP1101 IPTV-Box. On the VGA-Port
we get a normal signal.
Here is the link to the Mambux-Project: http://www.mambux.de
Cc: Keith Packard <keithp@keithp.com>
Cc: Dave Airlie <airlied@linux.ie>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Signed-off-by: Stefan Husemann <shusemann@googlemail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
I'm sure everyone knows this, but I didn't, so I googled it, and found a
nice explanation from Linus. Might be worth sticking in Documentation.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/memcontrol.c:318: warning: `mem_cgroup_is_obsolete' defined but not used
[akpm@linux-foundation.org: simplify as suggested by Balbir]
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Update information about locking in JBD revoke code.
Reported-by: Lin Tan <tammy000@gmail.com>.
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
While better than get_user_pages(), the usage of gupf(), especially the
return values and the fact that it can potentially only partially pin the
range, warranted some documentation.
Signed-off-by: Andy Grover <andy.grover@oracle.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Change cb6ff20807 ("NOMMU: Support XIP on
initramfs") seems to have broken booting from initramfs with /sbin/init
being a hardlink.
It seems like the logic required for XIP on nommu, i.e. ftruncate to
reported cpio header file size (body_len) is broken for hardlinks, which
have a reported size of 0, and the truncate thus nukes the contents of the
file (in my case busybox), making boot impossible and ending with runaway
loop modprobe binfmt-0000 - and of course 0000 is not a valid binary
format.
My fix is to only call ftruncate if size is non-zero which fixes things
for me, but I'm not certain whether this will break XIP for those files on
nommu systems, although I would guess not.
Signed-off-by: Randy Robertson <rmrobert@vmware.com>
Acked-by: David Howells <dhowells@redhat.com>
Acked-by: Paul Mundt <lethal@linux-sh.org>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Pointed out by Roland. The bug was recently introduced by me in
"forget_original_parent: split out the un-ptrace part", commit
39c626ae47.
Since that patch we have a window after exit_ptrace() drops tasklist and
before forget_original_parent() takes it again. In this window the child
can do ptrace(PTRACE_TRACEME) and nobody can untrace this child after
that.
Change ptrace_traceme() to not attach to the exiting ->real_parent. We
don't report the error in this case, we pretend we attach right before
->real_parent calls exit_ptrace() which should untrace us anyway.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Do a bit of reformatting on the Unevictable-LRU documentation.
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Point the UNEVICTABLE_LRU config option at the documentation describing
the option.
Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
commit ddb53d48da ("fbdev: remove cyblafb
driver") removed drivers/video/cyblafb.c, but not its .h file
Signed-off-by: Joe Perches <joe@perches.com>
Cc: Krzysztof Helt <krzysztof.h1@wp.pl>
Cc: "Jani Monoses" <jani@ubuntu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
After the introduction of resource counters hierarchies
(28dbc4b6a0) the prototypes of
res_counter_init() and res_counter_charge() have been changed.
Keep the documentation consistent with the actual function prototypes.
Signed-off-by: Andrea Righi <righi.andrea@gmail.com>
Cc: Paul Menage <menage@google.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The "simplify spi_write_then_read()" patch included two regressions from
the 2.6.27 behaviors:
- The data it wrote out during the (full duplex) read side
of the transfer was not zeroed.
- It fails completely on half duplex hardware, such as
Microwire and most "3-wire" SPI variants.
So, revert that patch. A revised version should be submitted at some
point, which can get the speedup on standard hardware (full duplex)
without breaking on less-capable half-duplex stuff.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: <stable@kernel.org> [2.6.28.x, 2.6.29.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Impact: (nearly) trivial
The patch
commit da654b74bd
Author: Srinivasa Ds <srinivasa@in.ibm.com>
Date: Tue Sep 23 15:23:52 2008 +0530
signals: demultiplexing SIGTRAP signal
forgot to update the NSIGTRAP define in asm-generic/siginfo.h to the new
number of sigtrap subcodes. Nothing in the tree seems to use it, but
presumably something in user space might. So update it.
Cc: Srinivasa Ds <srinivasa@in.ibm.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Do not allow modes with unsupported pixel depth. Otherwise, one can hang
a computer by setting incorrect value with fbset command.
Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Fix filemap.c kernel-doc warnings:
Warning(mm/filemap.c:575): No description found for parameter 'page'
Warning(mm/filemap.c:575): No description found for parameter 'waiter'
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Include <linux/types.h> in fiemap.h. Sam Ravnborg pointed out that this
was missing in this newly-exported header which uses the __u32 and __u64
types.
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
sisfb incorrectly sets the length of the color fields to 6 bits
for PSEUDOCOLOR modes, even though 8 bits are always used per pixel.
Fix this by setting the length to 8.
Signed-off-by: Michal Januszewski <spock@gentoo.org>
Cc: Thomas Winischhofer <thomas@winischhofer.net>
Acked-by: Krzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
sa1100fb incorrectly sets the length of the color fields to 8 bits for
PSEUDOCOLOR modes for which only 4 bits are used per pixel. Fix this by
setting the length to 4 bits for these modes.
Signed-off-by: Michal Januszewski <spock@gentoo.org>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
s3fb incorrectly sets the length of the color fields to 6 bits for
PSEUDOCOLOR modes, even though 8 or 4 bits are used per pixel. Fix this
by setting the length to 8 or 4, respectively.
Signed-off-by: Michal Januszewski <spock@gentoo.org>
Acked-by: Ondrej Zajicek <santiago@crfreenet.org>
Cc: Krzysztof Helt <krzysztof.h1@poczta.fm>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| ipc/mq_sysctl.c:26: warning: 'get_mq' defined but not used
Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
When an HFS filesystem is unmounted, it leaks a 2-page bitmap. Also,
under extreme memory pressure, it's possible that hfs_releasepage() may
use a tree pointer that has not been initialized, and if so, the release
request should just be rejected.
[akpm@linux-foundation.org: free_pages(0) is legal, remove obvious comment]
Signed-off-by: Dave Anderson <anderson@redhat.com>
Tested-by: Eugene Teo <eugeneteo@kernel.sg>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Data sheet at:
http://www.sensirion.ch/en/pdf/product_information/Datasheet-humidity-sensor-SHT1x.pdf
These sensors communicate over a 2 wire bus running a device specific
protocol. The complexity of the driver is mainly due to handling the
substantial delays between requesting a reading and the device pulling the
data line low to indicate that the data is available. This is handled by
an interrupt that is disabled under all other conditions.
I wasn't terribly clear on the best way to handle this, so comments on
that aspect would be particularly welcome!
Interpretation of the temperature depends on knowing the supply voltage.
If configured in a board config as a regulator consumer this is obtained
from the regulator subsystem. If not it should be provided in the
platform data.
I've placed this driver in the hwmon subsystem as it is definitely a
device that may be used for hardware monitoring and with it's relatively
slow response times (up to 120 millisecs to get a reading) a caching
strategy certainly seems to make sense!
Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
