It turns out that USB devices suck when it comes to powermanagement

issues :(
A number of patches have been submitted near the end of this kernel

release cycle that add new device ids to the quirk table in the kernel

to disable autosuspend for specific devices.  However, a number of

developers are very worried that even with the testing that has been

done, once 2.6.23 is released, we are going to get a whole raft of angry

users when their devices break in nasty ways.
As an example, it seems that almost 2/3 of all USB printers just can not

handle autosuspend.  And there's a _lot_ of USB printers out there...
When researching how other operating systems handle this, it was found

out that they use a whitelist of devices that are able to properly

suspend.  So, in the future, that is how we are going to handle this.
These two patches address the need today to have users machines still

work, even if they might draw more power than they possibly could (which

is not any more than they did in 2.6.22.)
These patches do two things:

  - disable USB autosuspend on all devices except for USB hubs.  This

    can be easily overridden by userspace to turn on autosuspend for

    devices that a user wants to.  HAL will use a whitelist in the

    future for these types of devices.

  - revert the usb-storage autosuspend patch.  This breaks a number of

    devices out there that can not handle suspend properly, _AND_ the

    current patch is broken even for devices that do work properly under

    some situations.  Data loss is not a good thing to have happen, so

    this patch is reverted for now.  Oliver has more specifics about the

    issues involved here if anyone is curious.
The "disable autosuspend" patch has been in the -mm tree for a while,

and is being shipped by Ubuntu and Red Hat in their bleeding-edge

kernels in order to handle the huge number of broken devices.  openSUSE

will also get this patch for its next kernel release once the suse

developers return from wondering around the...
[ message continues ]

Not related to the patch for 2.6.23, but I have a gut feeling that

something might be done the wrong way later:
If I understand you correctly, you are saying that I will have to

install HAL for getting a whitelist for in-kernel functionality?
It is a good thing if userspace can add currently missing devices to
cu

Adrian
-- 
       "Is there not promise of rain?" Ling Tan asked suddenly out

        of the darkness. There had been need of rain for many days.

       "Only a promise," Lao Er said.

                                       Pearl S. Buck - Dragon Seed
-

Your meaning isn't entirely clear.  Presumably HAL will contain such a

whitelist.  But there's nothing to stop you from setting up your own

whitelist via udev scripts, or even turning autosuspend on or off by 
It's not clear that this sort of approach will turn out to be workable.

Whitelists/blacklists do okay in the kernel when they refer to a

relatively small subset of devices.  However in this case I have the

impression that we're talking about roughly a 50/50 split.  Keeping an

in-kernel list with even 10% of all existing USB devices simply isn't

feasible.
Besides, is it really that much harder for userspace to modify device

settings as the devices are detected than for it to modify an in-kernel

whitelist just once?  Don't forget about possible races: Devices may

already have been detected and configured before userspace was able to

modify the whitelist.
Alan Stern
-

What about this is not feasible?
The amount of work for maintaining the list is the same:
No matter whether it's in-kernel or in the userspace, you need a list of

working devices in some machine readable format.
Whether this gets used by the kernel, by userspace, or both, shouldn't

make any difference.
Kernel image size can be a problem in some cases, but an in-kernel list 
Above you said "there's nothing to stop you from ... even turning

autosuspend on or off by hand".
If this will already be supported race-free, which races will still be
cu

Adrian
-- 
       "Is there not promise of rain?" Ling Tan asked suddenly out

        of the darkness. There had been need of rain for many days.

       "Only a promise," Lao Er said.

                                       Pearl S. Buck - Dragon Seed
-

Well, size is one problem I had in mind.  There are a _lot_ of USB

devices in existence.
But mainly it's a question of maintenance and modification.  Kernel

developers don't really enjoy maintaining black- or whitelists of

devices, together with all the work involved in sorting through the

issues when somebody posts an email saying "My device doesn't work!".
Also, modifying device lists in the kernel tends to be a slow process,

involving at least one kernel release cycle.  It's much easier for

people to maintain userspace databases.  Now I realize you proposed

there be a userspace interface for modifying the kernel's whitelist --

but if you're going to do that, why not put the entire whitelist in

userspace to begin with?
Maybe you're concerned about propagating updates as painlessly as

possible -- if the whitelist is in the kernel then every kernel release

would include an update.  But in userspace it's possible to do updates

even more quickly and painlessly.  For example, there could be a

network server available for both interactive lookups and automatic 
You _can't_ change the autosuspend setting for a device that hasn't yet

been detected; you can only do it after detection.  But you _can_

modify a whitelist either before or after a device is detected; any

such modifications won't affect the already-existing devices.
Does that answer your question?
Alan Stern
-

No matter whether the list is in userspace or in the kernel, maintaining

it is exactly the same job of adding entries into some machine readable

list (no matter whether it's a C struct or a CSV list that later gets

converted).
This could be the kernel developers or some external sf project that 
No, what I'm concerned about is that this would require userspace for 
cu

Adrian
-- 
       "Is there not promise of rain?" Ling Tan asked suddenly out

        of the darkness. There had been need of rain for many days.

       "Only a promise," Lao Er said.

                                       Pearl S. Buck - Dragon Seed
-

If done right (and autosuspend now is), there is no "required" userspace.
If you want autosuspend, you just say so. The kernel doesn't do it by

default. This is not about "user space required" - it's about "user space

can ask for it if it wants to".
Notice? There doesn't even have to be any blacklists/whitelists at all. It

really can be just an application that allows the user to check or uncheck

the capability (with a warning saying something like: "Some USB devices

may disconnect when suspended - if this affects you, uncheck this").
That's why the kernel shouldn't set policy. It's a *good* thing to just

expose the capabilities, but not necessarily use them! 
		Linus

-

What is not policy is the blacklist or whitelist information.
And I'm also a bit concerned why "is policy" is that much a reason

against setting *reasonable default policies* without requiring the user

to do various things in userspace.
Especially since this creates some nasty interdependencies between the

kernel and userspace.
And as an example, couldn't you equally say it's wrong that the kernel

enables DMA on disks instead of leaving it to userspace?
We've already seen the udev disaster where upgrading from Debian 3.1 to

Debian 4.0 means upgrading from kernel 2.6.8 to 2.6.18 with the udev

version in Debian 3.1 not supporting kernel 2.6.18 and the udev version

in Debian 4.0 not supporting kernel 2.6.8, and I don't have a good

feeling about outsourcing more and more things to userspace tools not 
cu

Adrian
-- 
       "Is there not promise of rain?" Ling Tan asked suddenly out

        of the darkness. There had been need of rain for many days.

       "Only a promise," Lao Er said.

                                       Pearl S. Buck - Dragon Seed
-

"Don't autosuspend" _is_ a reasonable default policy.  It's what Linux 
No it doesn't.  If the kernel fails to provide the mechanism there's

nothing that userspace can do about it anyway.  If the kernel does

provide the mechanism and userspace ignores it, then things continue to 
It's not analogous.  Autosuspend involves setting an idle-delay time,

which depends on the type of device and how it is being used.  DMA

doesn't involve anything like that.
But forget about the delay for the moment.  If there were a high

percentage of disk drives which would fail when DMA was enabled, then

yes, the decision should be left to userspace.  If the percentage is

low enough (and shrinking as vendors become more clueful) then moving

the decision into the kernel is acceptable.  At the moment USB 
This isn't a question of not being able to boot, like the udev fiasco;

this is a question of saving a few watts of power.  While it may be

important for laptop users, it is not critical.
Alan Stern
-

Let me paraphrase the latter:
Given a distribution shipping with kernel 2.6.23 released in 2007.
What is the maximum amount of userspace I might have to upgrade

if I'll want to use kernel 2.6.43 released in 2011 (sic) with this

distribution?
E.g. when looking at the reverse dependencies of libhal, it would not be

funny if kernel 2.6.43 required a more recent version of HAL.
cu

Adrian
-- 
       "Is there not promise of rain?" Ling Tan asked suddenly out

        of the darkness. There had been need of rain for many days.

       "Only a promise," Lao Er said.

                                       Pearl S. Buck - Dragon Seed
-

I can't speak for other parts of the kernel or userspace.  Concerning

USB autosuspend, you should not have to upgrade anything.
You might end up getting better power savings if you did upgrade, but

failing to upgrade wouldn't make your power usage any worse.
Alan Stern
-

Adrian, what's the point of answering your questions, WHEN YOU DON'T EVEN

READ THE ANSWERS!
So stop repeating your inane question, and instead LISTEN to what people

are saying.
There is *no* requirement what-so-ever on user space. End of story.
If user-space doesn't tell devices to go to autosuspend, they just won't

do so. But this has nothing to do with white-lists, black-lists, 2.6.43,

or your HAL version.
That black-listing was a mistake. We got over it. Now PLEASE you get over

it too!
		Linus

-

Adrian, please note that this is NOT the normal "suspend to ram/disk" stuff

that is being discussed / affected here.  But rather something brand new

(to Linux), the automatic powerdown (well, nearly) of idle USB devices

during regular running.
Things will work just fine without chewing up gobs of memory in a futile effort

to list everything inside the kernel.  Devices will plug in and work fine

(which they didn't in 2.6.23 until this stuff got reverted) the same as always.
To gain the last xx% in power savings, some userspace support may be needed,

that's all.  And with the pace of new/updated USB devices coming/going these days,

userspace is really the only appropriate place for this kind of stuff.
Cheers

-

Space saving has it's place, but there's also the point that for the 
It creates one more userspace _ABI_ for something that doesn't

necessarily need one.
Perhaps I'm wrong and people have learnt the lesson from the udev

disaster that ABIs used by stuff like udev or HAL are _userspace ABIs_
cu

Adrian
-- 
       "Is there not promise of rain?" Ling Tan asked suddenly out

        of the darkness. There had been need of rain for many days.

       "Only a promise," Lao Er said.

                                       Pearl S. Buck - Dragon Seed
-

But it isn't completely in-kernel.  It is policy, and policy belongs in

userspace.
The kernel provides the mechanism for autosuspending idle devices and

setting the idle-delay length.  But userspace must be responsible for

deciding what devices to autosuspend and how long the idle delays

should be.
Alan Stern
-

Yeah.
In general, I think the USB blacklist/whitelists are generally a sign of

some deeper bug.
We used to have a lot of those things due to simply incorrect SCSI

probing, causing devices to lock up because Linux probed them with bad or

unexpected modepages etc. I suspect we still have old blacklist entries

from those days that just never got cleaned up, because nobody ever dared

remove the blacklist entry.
We should strive to make the default behaviour be so safe that we never

need a black-list (or a whitelist), and basically consider blacklists to

be not a way to "fix up a device", but a way to avoid some really serious

AND *RARE* error.
The moment you have lots of devices having the same blacklist entry,

that's a sign that the blacklist is wrong, and the subsystem itself is

likely doing something bad!
So, I would seriously suggest:

 - look at USB quirks that have more than ten entries (and the entries

   aren't just the exact same device in various guises)

 - start considering that feature to be something that is known broken,

   and shouldn't be done AT ALL by default.

 - have some way to enable some extension on a device-by-device basis from

   the /sysfs interface, and then users can enable those things on their

   own with a graphical interface or something (or using whitelists in

   user space saying "ok, this device can actually do this")

 - REMOVE THE DAMN QUIRK
It looks like the current situation now is that the latest autosuspend

patches did basically everything but the last point.
Btw, this is in no way just an AUTOSUSPEND issue. The USB layer has a

*lot* of these quirks. They are often called "UNUSUAL_DEV()", but the

thing is, some of those things seem to be so usual that the naming is

dubious, and thus calling it a "quirk" or "unusual" is pretty dubious too. 
For example, why do we have that US_FL_MAX_SECTORS_64 at all? The fact

that some USB device is broken with more than 64 sectors would seem to

indicate that Windows *ne...
[ message continues ]

Well, ub does that today. And there is a measurable performance differential
I'm afraid this is valuable. However, a number of devices only return

garbage as residue if the transfer length is greater than 32KB. Limiting

that would trim this blacklist, I think. The vast majority of devices

work correctly in this regard, and ub checks the residue without any
It has something to do with the way our partition detection works. Linux

tends to rely on the reported device size. Windows reads the first block

and then goes further based on its contents. If we exterminate partitioning

code which uses the reported device size for autodetection, then this
This is being worked upon. The recent change for floppies eliminated

a big number of those.
-- Pete

-

I don't just suspect -- I know for a fact that we do.  Partly because

of laziness and partly because of not being able to verify that an
In general I agree.  However there are some problems for which nobody 
Yes, none of those USB_QUIRK_NO_AUTOSUSPEND entries are needed any

more.  They can all be removed and handed over to the HAL people as a 
You have concentrated your attention on the list for usb-storage,
That's true now, but it wasn't always.  Until the last year or so,

cdrecord wouldn't work properly with USB CD drives having a 64-sector

limit unless the user added a particular command-line argument.
In fact, setting max_sectors down to 64 is probably overkill -- 120

ought to be enough.  But there may have been one or two oddball devices

that really did have a 32-KB limit, and better safe than sorry.  At one

point an engineer from Genesys said their devices did, although they do

seem to work perfectly well with 64-KB transfers (and that's what 
Windows does indeed ignore the residue field, as far as I can tell.
But this is a rather tricky thing.  The USB mass-storage spec

specifically says that one way a device can signal a short transfer is

to pad the data with 0s to the requested length and then set the

residue to indicate how much of the data is valid.  If we ignore the

residue then we run a risk of misinterpreting the 0s as valid data.
Now in practice this doesn't matter much because short transfers of

block data (READ_10) generally involve other errors that would show up

anyway, and for non-block data (MODE SENSE) the padding probably

wouldn't matter.  Still it seems like a dangerous sort of thing to do,

which is why I have resisted it.
(And by the way, there _definitely_ are devices which use this
This is another hard case.  No, we aren't doing anything wrong.  If

there are any patterns we haven't seen, we aren't aware of them.  :-)

You might think that if a device claims to have an odd number of

sectors then it must be wrong, but this turns out n...
[ message continues ]

This is true. First, there are HID_QUIRK_RDESC_* quirks, which we use to

fix up badly broken report descriptor of certain devices before it enters

the HID parser. There is nothing much we can do about them - these are

just workarounds for really broken devices that don't follow the HID

specification, but we can easily fix the things on the fly. Usually, these

devices are handled in Windows by specialized driver, but if we fix the

descriptor, we can use usbhid to handle them.
For the rest of the HID quirks -- most of them are also workarounds for

broken classess of devices. Usually, they claim to be HID-compliant device

in their file descriptor, but they do not follow the spec (they send

inverted axes values, send usage codes that violate the specification,

etc), but we can easily work around these bugs by a few lines of code and

let the devices to be handled by usbhid flawlessly. I guess this is worth

it.
Probably the only quirk entry that might be considered to be removed is

HID_QUIRK_NOGET, I'd say.
Thanks,
--

Jiri Kosina

-

The reason for this is that the only way to write a userspace "driver"

for USB devices on Windows versions prior to Vista was to be a HID

device.  Your userspace program could then easily grab the device and

control it.
This could be fixed in Linux by providing a way to have driver

"heirachy" for USB whereby a vendor/product id providing driver would

take a higher priority than a class driver.
But we've been talking about that for over 7 years now :)
thanks,
greg k-h

-

We do have some code that looks for unneeded entries.  When found by an

end-user (which confirms that the entry can be removed), it asks the user
We generally do strive for such a thing.  Over the years, we've made

several changes to the way the SCSI core works (especially in the probing

department) to allow us to remove all sorts of special-case code and quirk
It's worth pointing out that performance drops like a stone as this number
I think this last point is key.  I'm unwilling to sacrifice error detection

on properly working devices to enable error-prone use on clearly buggy
As far as I know, Windows doesn't need this because of the way FAT and NTFS

work.  They never use the end of the disk (by more than a few sectors, or
I've been meaning to start sending e-mails to see if we can get rid of

these.  Most of the devices which required it were UFI, which reports "LUN

not present" in a goofy way.  We fixed the code to detect it properly, but

there are still quite a few devices out there that don't implement the

correct (if goofy) method.
Most of those entries (which are for UFI devices) can go, if we get a

volunteer to take the e-mail addresses listed in unusual_devs.h and work

the list.
Matt
--=20

Matthew Dharm                              Home: mdharm-usb@one-eyed-alien.=

net=20

Maintainer, Linux USB Mass Storage Driver
Sir, for the hundreth time, we do NOT carry 600-round boxes of belt-fed=20

suction darts!

					-- Salesperson to Greg

User Friendly, 12/30/1997

Does anybody have good performance figures, using a high-quality

device?  This is the sort of thing where it helps to have some real

numbers.
Alan Stern
-

Exactly.  The kernel will by default get the device up and working.  Any

capabilities to be changed after it is working can be done by userspace

with a "whitelist" type program that can properly tell the kernel that

this specific device can be safely suspended.
If you decide to do this in a small bash script, or in

HAL/udevd/DeviceKit/whatever, it all doesn't matter to the kernel.
thanks,
greg k-h

-