Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Hans de Goede]

Hi all,

Please keep me CC-ed I'm not on the list. I just found out about this thread 
while ivnestegating some autosuspend problems, which I will describe in another 
list.

stern at rowland  wrote:
 > Linus Torvalds wrote:
 > > - US_FL_FIX_CAPACITY:
 > > This is a generic SCSI issue, not a USB one, and maybe there are
 > > better solutions to it. Are we perhaps doing something wrong? Is
 > > there some patterns we haven't seen? Why do we need this, when
 > > presumably Windows does not?
 >
 > Why doesn't Windows need this? For all we know, it does. Has anybody
 > ever tried forcing Windows to read the sector beyond the end of one of
 > these buggy devices?

I haven't but I'm pretty sure it will crash my hp usb printer (with builtin 
cardreader)

 > For one reason or another, Linux supports filesystems/partitioning
 > schemes which do need to access the last sector (EFI GUID, md, maybe
 > others). Some devices are so buggy that trying to read the nonexistent
 > "last" sector causes them to lock up, requiring a power cycle.
 > Obviously we can't probe for this sort of behavior. (There was one
 > report of a device which _could_ read its last sector correctly, but
 > only if the transfer was exactly 1 sector long! Attempts to read two
 > sectors starting from the second-to-last sector would cause it to
 > crash.)

Yes and the reporter of that one device (a HP PSC1350) would be me, I even 
wrote a patch introducing a new quirk for this (shoot me, I don't like quirks 
either, but if we can choose between making some device work and not 
introducing a quirk, I say make the device work!)

Talking about this patch (posted to the usb-storage list) I haven't received 
any feedback, any chance this patch could get integrated soon? I have found 
another Linux user with the same printer and the same problem who has 
independently verified my patch fixes it. Currently a third Linux using owner 
of such a device has contacted me, I'm waiting for his feedback if the patch 
helps him too, but I assume it will. That makes 3 users who have jumped through 
many hoops to get it to work, so there are probably many other users who have 
just given up, or even returned to that other OS!

I'm pretty sure the only reason why that other OS doesn't crash the printer is 
because it normally doesn't try to read the last sector, I haven't tried as I 
no longer have that other OS on any computer in my home.

Also I think it might be an idea to have an option to easily disable the 
partition reading code which tries to read the end of the disk, this seems to 
cause problems in various places.

Regards,

Hans

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Joerg Schilling]

> 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. 

This is a bug that is known since ~ 3 years and that has been fixed 
_very_ recently. It was still present in 2.6.21.7 a few weeks ago.

And BTW: the limit was not 64 sectors but ~13 sectors. 64 sectors would be at 
least 128 kB but the limit was ~ 32k.





Jörg

-- 
 EMail:joerg@schily.isdn.cs.tu-berlin.de (home) Jörg Schilling D-13353 Berlin
       js@cs.tu-berlin.de                (uni)  
       schilling@fokus.fraunhofer.de     (work) Blog: http://schily.blogspot.com/
 URL:  http://cdrecord.berlios.de/old/private/ ftp://ftp.berlios.de/pub/schily

[GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Greg KH]

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 woods of the Czech Republic
next week.

Please pull from:
	master.kernel.org:/pub/scm/linux/kernel/git/gregkh/usb-2.6.git/

The full patches will be sent to the linux-usb-devel mailing list, if
anyone wants to see them.

thanks,

greg k-h


 drivers/usb/core/quirks.c      |    6 ++++++
 drivers/usb/storage/scsiglue.c |   13 ++++---------
 drivers/usb/storage/usb.c      |   27 +++++++--------------------
 3 files changed, 17 insertions(+), 29 deletions(-)

---------------

Alan Stern (1):
      USB: disable autosuspend by default for non-hubs

Greg Kroah-Hartman (1):
      Revert "usb-storage: implement autosuspend"

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Adrian Bunk]

On Thu, Sep 13, 2007 at 06:33:21AM -0700, Greg KH wrote:
> 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.
>...

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
whitelists, but the whitelist itself should be in the kernel.

> thanks,
> 
> greg k-h
>...

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

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Alan Stern]

On Thu, 13 Sep 2007, Adrian Bunk wrote:

> > 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.
> >...
> 
> 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?

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 
hand.

> It is a good thing if userspace can add currently missing devices to
> whitelists, but the whitelist itself should be in the kernel.

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

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Adrian Bunk]

On Thu, Sep 13, 2007 at 11:20:42AM -0400, Alan Stern wrote:
> On Thu, 13 Sep 2007, Adrian Bunk wrote:
> 
> > > 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.
> > >...
> > 
> > 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?
> 
> 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 
> hand.
> 
> > It is a good thing if userspace can add currently missing devices to
> > whitelists, but the whitelist itself should be in the kernel.
> 
> 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.

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 
doesn't have to be mandatory but could be made selectable in kconfig.

> 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.

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
possible?

> Alan Stern

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

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Alan Stern]

On Thu, 13 Sep 2007, Adrian Bunk wrote:

> > > It is a good thing if userspace can add currently missing devices to
> > > whitelists, but the whitelist itself should be in the kernel.
> > 
> > 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.
> 
> 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 
> doesn't have to be mandatory but could be made selectable in kconfig.

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 
queries from HAL.

> > 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.
> 
> 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
> possible?

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

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Greg KH]

On Thu, Sep 13, 2007 at 12:07:15PM -0400, Alan Stern wrote:
> 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.

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

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Linus Torvalds]

On Thu, 13 Sep 2007, Alan Stern wrote:
> 
> 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!".

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 *never* does more than 64 sectors, and that in turn 
means that pretty much *no* devices have ever been tested with anything 
bigger.

So why not make the 64 sector limit be the default? Get rid of the quirk: 
we already allow people to override it in /sys if they really want to, but 
realistically, it's probably not going to make any difference what-so-ever 
for *any* normal load. So we seem to have a quirk that really doesn't buy 
us anything but headache.

Other quirks worth looking at (but likely unfixable) are:
 - US_FL_IGNORE_RESIDUE:
	Does this really matter? Can we not just always do the 
	US_FL_IGNORE_RESIDUE thing? Windows must not be doing what we're 
	doing.
 - US_FL_FIX_CAPACITY: 
	This is a generic SCSI issue, not a USB one, and maybe there are 
	better solutions to it. Are we perhaps doing something wrong? Is 
	there some patterns we haven't seen? Why do we need this, when 
	presumably Windows does not?
 - US_FL_SINGLE_LUN:
	At least a few of these seem to indicate that the real problem 
	could be detected dynamically ("device reports Sub=ff") rather 
	than with a quirk. Quirks are unmaintainable (and change), but 
	noticing when devices return impossible values and going into a 
	"safe mode" is just defensive programming.

> 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 
> queries from HAL.

For a lot of these things, you probably do not need a whitelist *at*all*!

IOW, just default to something safe (the 64 sector example), and then 
perhaps allow people to explicitly play with their settings in a hardware 
manager. People actually tend to *like* being able to tweak meaningless 
things, and it makes them feel in control. So you'd have the Gentoo people 
who want to optimize their iPod access times by 0.2% by raising the 
maximum sector number - good for them! They'll feel empowered, and if it 
stops working, they know it was because of something *they* did.

So at least in some cases, I think we should "default to stupid, but give 
users rope".

		Linus

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Alan Stern]

On Thu, 13 Sep 2007, Linus Torvalds wrote:

> 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.

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
entry is no longer needed.

> 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.

In general I agree.  However there are some problems for which nobody 
has been able to come up with another solution.  See below.

> 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.

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 
starting 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. 

You have concentrated your attention on the list for usb-storage,
but the usbhid driver also has an impressively long quirks list.

> 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 *never* does more than 64 sectors, and that in turn 
> means that pretty much *no* devices have ever been tested with anything 
> bigger.
> 
> So why not make the 64 sector limit be the default? Get rid of the quirk: 
> we already allow people to override it in /sys if they really want to, but 
> realistically, it's probably not going to make any difference what-so-ever 
> for *any* normal load. So we seem to have a quirk that really doesn't buy 
> us anything but headache.

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 gives them).

> Other quirks worth looking at (but likely unfixable) are:
>  - US_FL_IGNORE_RESIDUE:
> 	Does this really matter? Can we not just always do the 
> 	US_FL_IGNORE_RESIDUE thing? Windows must not be doing what we're 
> 	doing.

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
signalling method.  In fact, Linux contains a driver that does it.)

>  - US_FL_FIX_CAPACITY: 
> 	This is a generic SCSI issue, not a USB one, and maybe there are 
> 	better solutions to it. Are we perhaps doing something wrong? Is 
> 	there some patterns we haven't seen? Why do we need this, when 
> 	presumably Windows does not?

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 not to be true.

Why doesn't Windows need this?  For all we know, it does.  Has anybody
ever tried forcing Windows to read the sector beyond the end of one of
these buggy devices?

For one reason or another, Linux supports filesystems/partitioning
schemes which do need to access the last sector (EFI GUID, md, maybe
others).  Some devices are so buggy that trying to read the nonexistent
"last" sector causes them to lock up, requiring a power cycle.  
Obviously we can't probe for this sort of behavior.  (There was one
report of a device which _could_ read its last sector correctly, but
only if the transfer was exactly 1 sector long!  Attempts to read two
sectors starting from the second-to-last sector would cause it to
crash.)

There's a straightforward solution: Never try to use the last sector --
in effect, assume every device has the FIX_CAPACITY flag set.  Doing 
this universally could cause data loss, however, so again I have been 
opposed to it.

>  - US_FL_SINGLE_LUN:
> 	At least a few of these seem to indicate that the real problem 
> 	could be detected dynamically ("device reports Sub=ff") rather 
> 	than with a quirk. Quirks are unmaintainable (and change), but 
> 	noticing when devices return impossible values and going into a 
> 	"safe mode" is just defensive programming.

This is almost certainly a case where lots of the entries are no longer 
needed.  But it isn't easy to tell which ones can safely be removed.

The problem here isn't that the device reports impossible values -- 
what happens is that it responds to commands for any LUN, causing the 
kernel to think it is really multiple devices.

> For a lot of these things, you probably do not need a whitelist *at*all*!
> 
> IOW, just default to something safe (the 64 sector example), and then 
> perhaps allow people to explicitly play with their settings in a hardware 
> manager. People actually tend to *like* being able to tweak meaningless 
> things, and it makes them feel in control. So you'd have the Gentoo people 
> who want to optimize their iPod access times by 0.2% by raising the 
> maximum sector number - good for them! They'll feel empowered, and if it 
> stops working, they know it was because of something *they* did.
> 
> So at least in some cases, I think we should "default to stupid, but give 
> users rope".

This will work in some cases, but not in others.  In particular, it 
won't work when the values have to known at device-detection time.  
Once the sysfs files have been set up and the user can put in the 
correct values, it's already too late.

Still, I agree that we can get rid of MAX_SECTORS_64.  Similarly,
FIX_INQUIRY shouldn't be needed, since any device which does need it
would fail to work under Windows.  However the really popular flags are 
the ones which would be hardest to remove.

Alan Stern

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Matthew Dharm]

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On Thu, Sep 13, 2007 at 03:13:46PM -0400, Alan Stern wrote:
> On Thu, 13 Sep 2007, Linus Torvalds wrote:
> 
> > 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.
> 
> 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
> entry is no longer needed.

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
to drop us an e-mail so we can remove it.

> > 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.
> 
> In general I agree.  However there are some problems for which nobody 
> has been able to come up with another solution.  See below.

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
entries.

> > 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 *never* does more than 64 sectors, and that in turn 
> > means that pretty much *no* devices have ever been tested with anything 
> > bigger.
> > 
> > So why not make the 64 sector limit be the default? Get rid of the quirk: 
> > we already allow people to override it in /sys if they really want to, but 
> > realistically, it's probably not going to make any difference what-so-ever 
> > for *any* normal load. So we seem to have a quirk that really doesn't buy 
> > us anything but headache.
> 
> 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 gives them).

It's worth pointing out that performance drops like a stone as this number
goes down.

> > Other quirks worth looking at (but likely unfixable) are:
> >  - US_FL_IGNORE_RESIDUE:
> > 	Does this really matter? Can we not just always do the 
> > 	US_FL_IGNORE_RESIDUE thing? Windows must not be doing what we're 
> > 	doing.
> 
> 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
> signalling method.  In fact, Linux contains a driver that does it.)

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
devices.

> >  - US_FL_FIX_CAPACITY: 
> > 	This is a generic SCSI issue, not a USB one, and maybe there are 
> > 	better solutions to it. Are we perhaps doing something wrong? Is 
> > 	there some patterns we haven't seen? Why do we need this, when 
> > 	presumably Windows does not?
> 
> 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 not to be true.
> 
> Why doesn't Windows need this?  For all we know, it does.  Has anybody
> ever tried forcing Windows to read the sector beyond the end of one of
> these buggy devices?

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
so I'm told).

> There's a straightforward solution: Never try to use the last sector --
> in effect, assume every device has the FIX_CAPACITY flag set.  Doing 
> this universally could cause data loss, however, so again I have been 
> opposed to it.

I agree here.

> >  - US_FL_SINGLE_LUN:
> > 	At least a few of these seem to indicate that the real problem 
> > 	could be detected dynamically ("device reports Sub=ff") rather 
> > 	than with a quirk. Quirks are unmaintainable (and change), but 
> > 	noticing when devices return impossible values and going into a 
> > 	"safe mode" is just defensive programming.
> 
> This is almost certainly a case where lots of the entries are no longer 
> needed.  But it isn't easy to tell which ones can safely be removed.

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

-- 
Matthew Dharm                              Home: mdharm-usb@one-eyed-alien.net 
Maintainer, Linux USB Mass Storage Driver

Sir, for the hundreth time, we do NOT carry 600-round boxes of belt-fed 
suction darts!
					-- Salesperson to Greg
User Friendly, 12/30/1997

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Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Alan Stern]

On Thu, 13 Sep 2007, Matthew Dharm wrote:

> > 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 gives them).
> 
> It's worth pointing out that performance drops like a stone as this number
> goes down.

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

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Jiri Kosina]

On Thu, 13 Sep 2007, Alan Stern wrote:

> > 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.
> You have concentrated your attention on the list for usb-storage,
> but the usbhid driver also has an impressively long quirks list.

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

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Greg KH]

On Fri, Sep 14, 2007 at 10:55:46AM +0200, Jiri Kosina wrote:
> 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.

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

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Pete Zaitcev]

On Thu, 13 Sep 2007 09:43:13 -0700 (PDT), Linus Torvalds <torvalds@linux-foundation.org> wrote:

> So why not make the 64 sector limit be the default? Get rid of the quirk: 
> we already allow people to override it in /sys if they really want to, but 
> realistically, it's probably not going to make any difference what-so-ever 
> for *any* normal load. So we seem to have a quirk that really doesn't buy 
> us anything but headache.

Well, ub does that today. And there is a measurable performance differential
with usb-storage when driving rotating discs, or so I heard.

> Other quirks worth looking at (but likely unfixable) are:
>  - US_FL_IGNORE_RESIDUE:
> 	Does this really matter? Can we not just always do the 
> 	US_FL_IGNORE_RESIDUE thing? Windows must not be doing what we're 
> 	doing.

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
blacklist.

>  - US_FL_FIX_CAPACITY: 
> 	This is a generic SCSI issue, not a USB one, and maybe there are 
> 	better solutions to it. Are we perhaps doing something wrong? Is 
> 	there some patterns we haven't seen? Why do we need this, when 
> 	presumably Windows does not?

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
problem will fix itself.

>  - US_FL_SINGLE_LUN:
> 	At least a few of these seem to indicate that the real problem 
> 	could be detected dynamically ("device reports Sub=ff") rather 
> 	than with a quirk. Quirks are unmaintainable (and change), but 
> 	noticing when devices return impossible values and going into a 
> 	"safe mode" is just defensive programming.

This is being worked upon. The recent change for floppies eliminated
a big number of those.

-- Pete

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Adrian Bunk]

On Thu, Sep 13, 2007 at 12:07:15PM -0400, Alan Stern wrote:
> On Thu, 13 Sep 2007, Adrian Bunk wrote:
> 
> > > > It is a good thing if userspace can add currently missing devices to
> > > > whitelists, but the whitelist itself should be in the kernel.
> > > 
> > > 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.
> > 
> > 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 
> > doesn't have to be mandatory but could be made selectable in kconfig.
> 
> Well, size is one problem I had in mind.  There are a _lot_ of USB 
> devices in existence.

Kernel image size matters much for some uses, but not for all.

> 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?

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 
gets synced with the kernel during each merge window.

> 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 
> queries from HAL.
>...

No, what I'm concerned about is that this would require userspace for 
something that is completely in-kernel.

> Alan Stern

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

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Alan Stern]

On Thu, 13 Sep 2007, Adrian Bunk wrote:

> > 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 
> > queries from HAL.
> >...
> 
> No, what I'm concerned about is that this would require userspace for 
> something that is completely in-kernel.

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

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Linus Torvalds]

On Thu, 13 Sep 2007, Adrian Bunk wrote:
> 
> No, what I'm concerned about is that this would require userspace for 
> something that is completely in-kernel.

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

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Adrian Bunk]

On Thu, Sep 13, 2007 at 01:44:23PM -0700, Linus Torvalds wrote:
> 
> 
> On Thu, 13 Sep 2007, Adrian Bunk wrote:
> > 
> > No, what I'm concerned about is that this would require userspace for 
> > something that is completely in-kernel.
> 
> 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! 

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 
distributed with the kernel.

> 		Linus

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

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Adrian Bunk]

On Thu, Sep 13, 2007 at 11:28:42PM +0200, Adrian Bunk wrote:
> On Thu, Sep 13, 2007 at 01:44:23PM -0700, Linus Torvalds wrote:
> > 
> > 
> > On Thu, 13 Sep 2007, Adrian Bunk wrote:
> > > 
> > > No, what I'm concerned about is that this would require userspace for 
> > > something that is completely in-kernel.
> > 
> > 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! 
> 
> 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 
> distributed with the kernel.

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

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Linus Torvalds]

On Fri, 14 Sep 2007, Adrian Bunk wrote:
> 
> 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.

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

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Mark Lord]

Linus Torvalds wrote:
> 
> On Fri, 14 Sep 2007, Adrian Bunk wrote:
>> 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.
> 
> 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!

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

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Adrian Bunk]

On Fri, Sep 14, 2007 at 09:21:08AM -0400, Mark Lord wrote:
> Linus Torvalds wrote:
>> On Fri, 14 Sep 2007, Adrian Bunk wrote:
>>> 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.
>> 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!
>
> 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.

I am quite aware of this fact.

> 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.

Space saving has it's place, but there's also the point that for the 
normal desktop usage a few 100 kB of data wouldn't matter.

> 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.

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_
and have to be treated accordingly.

> Cheers

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

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Alan Stern]

On Fri, 14 Sep 2007, Adrian Bunk wrote:

> 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?

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

Re: [GIT PATCH] USB autosuspend fixes for 2.6.23-rc6

[Alan Stern]

On Thu, 13 Sep 2007, Adrian Bunk wrote:

> What is not policy is the blacklist or whitelist information.

That's debatable, but never mind.

> 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.

"Don't autosuspend" _is_ a reasonable default policy.  It's what Linux 
has been doing all along.

> Especially since this creates some nasty interdependencies between the 
> kernel and userspace.

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 
work the same as they always have.

> 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?

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 
autosuspend is not in this position, as we have learned painfully.

> 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 
> distributed with the kernel.

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