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Bjørn Mork 3edce1cf81 USB: cdc-wdm: implement IOCTL_WDM_MAX_COMMAND 
Userspace applications need to know the maximum supported message
size.

The cdc-wdm driver translates between a character device stream
and a message based protocol.  Each message is transported as a
usb control message with no further encapsulation or syncronization.
Each read or write on the character device should translate to
exactly one usb control message to ensure that message boundaries
are kept intact.  That means that the userspace application must
know the maximum message size supported by the device and driver,
making this size a vital part of the cdc-wdm character device API.

CDC WDM and CDC MBIM functions export the maximum supported
message size through CDC functional descriptors.  The cdc-wdm and
cdc_mbim drivers will parse these descriptors and use the value
chosen by the device.  The only current way for a userspace
application to retrive the value is by duplicating the descriptor
parsing. This is an unnecessary complex task, and application
writers are likely to postpone it, using a fixed value and adding
a "todo" item.

QMI functions have no way to tell the host what message size they
support.  The qmi_wwan driver use a fixed value based on protocol
recommendations and observed device behaviour.  Userspace
applications must know and hard code the same value.  This scheme
will break if we ever encounter a QMI device needing a device
specific message size quirk.  We are currently unable to support
such a device because using a non default size would break the
implicit userspace API.

The message size is currently a hidden attribute of the cdc-wdm
userspace API.  Retrieving it is unnecessarily complex, increasing
the possibility of drivers and applications using different limits.
The resulting errors are hard to debug, and can only be replicated
on identical hardware.

Exporting the maximum message size from the driver simplifies the
task for the userspace application, and creates a unified
information source independent of device and function class. It also
serves to document that the message size is part of the cdc-wdm
userspace API.

This proposed API extension has been presented for the authors of
userspace applications and libraries using the current API: libmbim,
libqmi, uqmi, oFono and ModemManager.  The replies were:

Aleksander Morgado:
 "We do really need max message size for MBIM; and as you say, it may be
  good to have the max message size info also for QMI, so the new ioctl
  seems a good addition. So +1 from my side, for what it's worth."

Dan Williams:
 "Yeah, +1 here.  I'd prefer the sysfs file, but the fact that that
  doesn't work for fd passing pretty much kills it."

No negative replies are so far received.

Cc: Aleksander Morgado <aleksander@lanedo.com>
Cc: Dan Williams <dcbw@redhat.com>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Acked-by: Oliver Neukum <oliver@neukum.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-03-25 13:32:20 -07:00
..
ABI Merge branch 'for_linus' of git://cavan.codon.org.uk/platform-drivers-x86 2013-03-03 10:16:19 -08:00
accounting doc: Remove unnecessary declarations from Documentation/accounting/getdelays.c 2012-11-26 14:22:21 +01:00
acpi ACPI / Documentation: refer to correct file for acpi_platform_device_ids[] table 2013-02-13 13:43:02 +01:00
aoe aoe: allow user to disable target failure timeout 2012-12-17 17:15:25 -08:00
arm fbdev changes for 3.8: 2012-12-15 13:03:48 -08:00
arm64 arm64: Add simple earlyprintk support 2013-01-22 17:51:01 +00:00
auxdisplay
backlight backlight: lp855x_bl: support new LP8557 device 2013-02-21 17:22:25 -08:00
blackfin Documentation: Fix typo in multiple files in Documentation 2012-04-16 14:37:13 +02:00
block cfq-iosched: enable full blkcg hierarchy support 2013-01-09 08:05:11 -08:00
blockdev nbd: update documentation and link to mailinglist 2013-02-27 19:10:22 -08:00
bus-devices ARM: OMAP2+: gpmc: generic timing calculation 2012-11-09 18:07:11 +05:30
cdrom
cgroups Merge branch 'for-3.9/core' of git://git.kernel.dk/linux-block 2013-02-28 12:52:24 -08:00
connector connector: Move cn_test.c away from NLMSG_PUT(). 2012-06-26 21:19:02 -07:00
console
cpu-freq cpufreq: Update Documentation for cpus and related_cpus 2013-02-02 00:01:16 +01:00
cpuidle Honor state disabling in the cpuidle ladder governor 2012-09-04 01:35:44 +02:00
cris CRIS: Update documentation 2012-04-03 13:09:18 +02:00
crypto KEYS: Document asymmetric key type 2012-10-08 13:50:12 +10:30
development-process
device-mapper md updates for 3.9 2013-03-05 17:22:08 -08:00
devicetree Merge 3.9-rc4 into usb-next 2013-03-25 10:05:37 -07:00
DocBook Merge branch 'drm-next' of git://people.freedesktop.org/~airlied/linux 2013-02-25 16:46:44 -08:00
driver-model lib: devres: Introduce devm_ioremap_resource() 2013-01-22 09:41:43 -08:00
dvb [media] get_dvb_firmware: Fix the location of firmware for Terratec HTC 2013-01-01 11:18:26 -02:00
early-userspace
EDID drm: Load EDID: Explain better how to write your own EDID firmware 2013-01-20 19:22:19 +10:00
extcon Documentation/extcon: porting guide for Android kernel switch driver. 2012-04-20 09:24:27 -07:00
fault-injection doc: fix quite a few typos within Documentation 2012-11-19 14:28:24 +01:00
fb Documentation: remove references to /etc/modprobe.conf 2012-03-30 16:03:15 -07:00
filesystems Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2013-02-26 20:16:07 -08:00
firmware_class firmware loader: document firmware cache mechanism 2012-11-14 15:07:18 -08:00
frv
hid HID: remove x bit from sensor doc 2012-12-14 08:48:59 +01:00
hwmon hwmon: (lm75) Fix tcn75 prefix 2013-03-18 21:19:49 +01:00
i2c i2c: Fix my e-mail address in drivers and documentation 2013-03-22 11:18:34 +01:00
i2o
ia64 doc: aliasing-test: close fd on write error 2012-09-01 09:57:10 -07:00
ide Documentation: remove references to /etc/modprobe.conf 2012-03-30 16:03:15 -07:00
infiniband IB/ipoib: Add rtnl_link_ops support 2012-09-20 16:49:17 -04:00
input Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input 2013-03-11 07:49:37 -07:00
ioctl USB: cdc-wdm: implement IOCTL_WDM_MAX_COMMAND 2013-03-25 13:32:20 -07:00
isdn Documentation: remove references to /etc/modprobe.conf 2012-03-30 16:03:15 -07:00
ja_JP
kbuild Merge branch 'kconfig' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild 2013-02-27 12:28:30 -08:00
kdump kexec: update URL of kexec homepage 2012-07-18 18:35:57 -07:00
ko_KR
laptops Documentation/laptops: remove depends on CONFIG_EXPERIMENTAL 2013-01-21 14:52:42 -08:00
leds Documentation: leds: update LP55xx family devices 2013-02-06 15:59:30 -08:00
m68k
make
memory-devices memory: emif: add basic infrastructure for EMIF driver 2012-05-02 00:10:49 -07:00
metag metag: Basic documentation 2013-03-02 20:09:50 +00:00
mips
misc-devices doc: fix quite a few typos within Documentation 2012-11-19 14:28:24 +01:00
mmc mmc: core: Extend sysfs to ext_csd parameters for RPMB support 2012-12-06 13:54:48 -05:00
mn10300
mtd
namespaces userns: Recommend use of memory control groups. 2013-01-26 22:20:06 -08:00
netlabel
networking net: docs: document multiqueue tuntap API 2013-03-06 14:56:10 -05:00
nfc NFC: Update pn544 documentation 2013-01-10 01:27:46 +01:00
parisc Documentation: Fix typo in multiple files in Documentation 2012-04-16 14:37:13 +02:00
PCI PCI/MSI: Enable multiple MSIs with pci_enable_msi_block_auto() 2013-01-24 17:25:13 +01:00
pcmcia
power PM / OPP: improve introductory documentation 2013-03-04 14:23:11 +01:00
powerpc powerpc: Documentation for transactional memory on powerpc 2013-02-15 17:02:25 +11:00
pps
prctl seccomp: Make syscall skipping and nr changes more consistent 2012-10-02 21:14:29 +10:00
pti
ptp
rapidio
RCU Merge branches 'urgent.2012.10.27a', 'doc.2012.11.16a', 'fixes.2012.11.13a', 'srcu.2012.10.27a', 'stall.2012.11.13a', 'tracing.2012.11.08a' and 'idle.2012.10.24a' into HEAD 2012-11-16 09:59:58 -08:00
s390 Documentation: remove references to /etc/modprobe.conf 2012-03-30 16:03:15 -07:00
scheduler sched: Remove __ARCH_WANT_INTERRUPTS_ON_CTXSW 2012-09-13 16:52:04 +02:00
scsi [SCSI] megaraid_sas: Version and Changelog update 2013-02-22 15:37:15 +00:00
security Documentation: fix Documentation/security/00-INDEX 2012-12-17 17:15:22 -08:00
serial tty: Update serial core API documentation 2013-01-15 21:57:44 -08:00
sh
sound ALSA: documentation: Fix typo in Documentation/sound 2013-03-17 10:12:13 +01:00
spi Documentation: remove __dev* attributes. 2013-01-03 15:57:16 -08:00
sysctl Documentation/sysctl/kernel.txt: document /proc/sys/shmall 2013-01-04 16:11:46 -08:00
target target: Simplify fabric sense data length handling 2012-09-17 17:12:58 -07:00
thermal Merge branch 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/rzhang/linux 2013-02-28 19:48:26 -08:00
timers
trace Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2013-03-11 07:54:29 -07:00
usb USB: report submission of active URBs 2012-11-11 18:10:46 -08:00
vDSO
video4linux [media] radio-si470x doc: add info about v4l2-ctl and sox+alsa 2013-02-13 17:33:20 -02:00
virtual Merge tag 'kvm-3.9-1' of git://git.kernel.org/pub/scm/virt/kvm/kvm 2013-02-24 13:07:18 -08:00
vm ksm: add some comments 2013-02-23 17:50:23 -08:00
w1 w1: w1_therm: Add force-pullup option for "broken" sensors 2013-02-18 13:55:24 -08:00
watchdog watchdog: core: dt: add support for the timeout-sec dt property 2013-03-01 12:48:36 +01:00
wimax
x86 Merge branch 'x86/microcode' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2013-02-22 19:22:52 -08:00
xtensa xtensa: initialize atomctl SR 2012-12-18 21:10:22 -08:00
zh_CN Driver core patches for 3.9-rc1 2013-02-21 12:05:51 -08:00
.gitignore
00-INDEX ImgTec Meta architecture changes for v3.9-rc1 2013-03-03 12:06:09 -08:00
applying-patches.txt
atomic_ops.txt Documentation: Memory barrier semantics of atomic_xchg() 2013-01-08 14:14:55 -08:00
bad_memory.txt
basic_profiling.txt
binfmt_misc.txt
braille-console.txt
bt8xxgpio.txt
btmrvl.txt
BUG-HUNTING
bus-virt-phys-mapping.txt
cachetlb.txt
Changes
circular-buffers.txt
clk.txt
coccinelle.txt coccicheck: Allow the user to give a V= (verbose) argument 2013-02-22 11:39:13 +01:00
CodingStyle Documentation: remove depends on CONFIG_EXPERIMENTAL 2013-01-11 11:38:03 -08:00
cpu-hotplug.txt doc: Add x86 CPU0 online/offline feature 2012-11-14 09:39:44 -08:00
cpu-load.txt
cputopology.txt
crc32.txt crc32: move long comment about crc32 fundamentals to Documentation/ 2012-03-23 16:58:37 -07:00
dcdbas.txt
debugging-modules.txt
debugging-via-ohci1394.txt
dell_rbu.txt
devices.txt firmware: remove last vestiges of dabusb 2012-11-21 13:03:01 -08:00
digsig.txt
DMA-API-HOWTO.txt Documentation/DMA-API-HOWTO.txt: fix typo 2013-02-27 19:10:23 -08:00
DMA-API.txt dma-debug: New interfaces to debug dma mapping errors 2012-10-24 17:06:43 +02:00
DMA-attributes.txt common: DMA-mapping: add DMA_ATTR_FORCE_CONTIGUOUS attribute 2012-11-29 03:30:34 -08:00
dma-buf-sharing.txt dma-buf: implement vmap refcounting in the interface logic 2013-02-27 15:13:36 +05:30
DMA-ISA-LPC.txt
dmaengine.txt
dontdiff x86: remove offsets.h from .gitignore and dontdiff 2012-11-19 14:10:53 +01:00
dynamic-debug-howto.txt dynamic_debug: dynamic hex dump 2013-01-17 12:19:09 -08:00
edac.txt Merge branch 'devel' 2012-07-29 21:11:05 -03:00
eisa.txt MCA: delete all remaining traces of microchannel bus support. 2012-05-17 19:06:13 -04:00
email-clients.txt
flexible-arrays.txt
futex-requeue-pi.txt
gcov.txt
gpio.txt gpiolib: provide provision to register pin ranges 2012-11-11 19:06:00 +01:00
highuid.txt
HOWTO HOWTO: fix double words typo 2012-12-10 15:54:27 +01:00
hw_random.txt
hwspinlock.txt
init.txt
initrd.txt Documentation/initrd.txt: Change the location of util-linux 2012-05-25 16:18:34 +02:00
intel_txt.txt Documentation: remove depends on CONFIG_EXPERIMENTAL 2013-01-11 11:38:03 -08:00
Intel-IOMMU.txt
io_ordering.txt
io-mapping.txt
iostats.txt
IPMI.txt ipmi: add options to disable openfirmware and PCI scanning 2013-02-27 19:10:21 -08:00
IRQ-affinity.txt
IRQ-domain.txt irqdomain: update documentation 2012-12-05 23:52:10 +00:00
IRQ.txt
irqflags-tracing.txt
isapnp.txt
java.txt
kernel-doc-nano-HOWTO.txt Kernel-doc: Convention: Use a "Return" section to describe return values 2012-11-27 21:08:57 +01:00
kernel-docs.txt
kernel-parameters.txt ImgTec Meta architecture changes for v3.9-rc1 2013-03-03 12:06:09 -08:00
kmemcheck.txt
kmemleak.txt
kobject.txt Documentation: Fix "struct kobj_type" to include newer members. 2012-09-04 16:06:34 -07:00
kprobes.txt
kref.txt kref: Add kref_get_unless_zero documentation 2012-11-28 18:36:06 +10:00
ldm.txt
local_ops.txt
lockdep-design.txt
lockstat.txt locking/stat: Fix a typo 2013-02-19 08:42:37 +01:00
lockup-watchdogs.txt
logo.gif
logo.txt
magic-number.txt wanrouter: completely decouple obsolete code from kernel. 2013-01-31 19:20:33 -05:00
Makefile mei: move doc files Documentation/misc-devices/mei 2012-05-09 13:59:09 -07:00
ManagementStyle Documentation: ManagementStyle: fixed typo 2012-06-28 12:03:15 +02:00
md.txt
media-framework.txt [media] Documentation/media-framework.txt: fix a sentence 2013-02-08 13:27:13 -02:00
memory-barriers.txt Documentation: Memory barrier semantics of atomic_xchg() 2013-01-08 14:14:55 -08:00
memory-hotplug.txt hotplug: update nodemasks management 2012-12-12 17:38:33 -08:00
mono.txt Documentation: remove references to /etc/modprobe.conf 2012-03-30 16:03:15 -07:00
mutex-design.txt
nommu-mmap.txt
numastat.txt
oops-tracing.txt
padata.txt
parport-lowlevel.txt
parport.txt Documentation: remove references to /etc/modprobe.conf 2012-03-30 16:03:15 -07:00
percpu-rw-semaphore.txt percpu-rw-semaphore: fix documentation typos 2012-09-26 19:56:15 +02:00
pi-futex.txt
pinctrl.txt drivers/pinctrl: grab default handles from device core 2013-01-23 16:39:51 +01:00
pnp.txt
preempt-locking.txt
printk-formats.txt Randy has moved 2013-03-08 15:05:34 -08:00
pwm.txt pwm: add devm_pwm_get() and devm_pwm_put() 2012-09-10 17:05:45 +02:00
ramoops.txt pstore/ftrace: Convert to its own enable/disable debugfs knob 2012-09-06 22:16:58 -07:00
rbtree.txt rbtree: move augmented rbtree functionality to rbtree_augmented.h 2012-10-09 16:22:40 +09:00
remoteproc.txt remoteproc: add rproc_report_crash function to notify rproc crashes 2012-09-18 12:53:22 +03:00
rfkill.txt
robust-futex-ABI.txt
robust-futexes.txt
rpmsg.txt Documentation: remove __dev* attributes. 2013-01-03 15:57:16 -08:00
rt-mutex-design.txt
rt-mutex.txt
rtc.txt rtc-proc: permit the /proc/driver/rtc device to use other devices 2012-10-06 03:05:01 +09:00
SAK.txt
SecurityBugs
serial-console.txt
sgi-ioc4.txt
sgi-visws.txt
SM501.txt
smsc_ece1099.txt mfd: smsc: Add support for smsc gpio io/keypad driver 2012-10-01 15:27:48 +02:00
sparse.txt Documentation/sparse.txt: document context annotations for lock checking 2012-12-17 17:15:23 -08:00
spinlocks.txt
stable_api_nonsense.txt
stable_kernel_rules.txt stable: Allow merging of backports for serious user-visible performance issues 2012-06-25 12:11:58 -07:00
static-keys.txt Documentation: Fix typo in multiple files in Documentation 2012-04-16 14:37:13 +02:00
SubmitChecklist
SubmittingDrivers
SubmittingPatches Randy has moved 2013-03-08 15:05:34 -08:00
svga.txt
sysfs-rules.txt
sysrq.txt sparc64: Add global PMU register dumping via sysrq. 2012-10-16 09:34:01 -07:00
unaligned-memory-access.txt
unicode.txt
unshare.txt
vfio.txt vfio: Trivial Documentation correction 2012-09-21 10:48:03 -06:00
VGA-softcursor.txt
vgaarbiter.txt
video-output.txt
vme_api.txt VME: Move API documentation to Documentation folder 2012-05-08 16:01:34 -07:00
volatile-considered-harmful.txt
workqueue.txt workqueue: reimplement WQ_HIGHPRI using a separate worker_pool 2012-07-13 22:24:45 -07:00
xz.txt
zorro.txt