2000-11-15 01:32:40

by Adam J. Richter

[permalink] [raw]
Subject: Re: Patch(?): linux-2.4.0-test11-pre4/drivers/sound/yss225.c compilefailure

In the particular case of yss225.c, I understand now that it
is ISA only, which is not hot pluggable, so __initdata should be fine;
however, I would like to respond to some other points that Jeff Garzik
raised.

Jeff Garzik wrote:
>Please err on the conservative side -- IMHO you shouldn't mark a driver
>as hotpluggable (by using the '__dev' prefix) unless you know it is
>necessary.

To the best of my knowledge, using __devinit does not "mark" a
driver as hot pluggable. All __devinit{,data} does is resolve to
__init{,data} if CONFIG_HOTPLUG is undefined, and resolve to nothing
if CONFIG_HOTPLUG is defined.

If a programmer errs in favor of __devinit, the result is
extra memory consumption under CONFIG_HOTPLUG. If a programmer
errs in favor of __init, the result is a crash during hot p
ug insertion. Avoiding crashes at the expensive of a pretty small
amount of memory usage is the more "conservative" way to err.


>Otherwise, you rob CONFIG_HOTPLUG people of some memory that could
>otherwise be freed at boot. And the number of CONFIG_HOTPLUG people is
>not small, it includes not only the CardBus users but USB users too...

We have been discussing this on linux-devel-usb. The
latest patches submitted to Linus and in 2.4.0-test10-pre{3,4}
support USB hot plugging regardless of whether CONFIG_HOTPLUG is
specified.


bash% find linux-2.4.0-test11-pre4/drivers/usb -type f | xargs egrep HOTPLUG
bash%


Having USB hot plugging without needing to build in PCI
hot plugging is useful, since there are lots of devices that lack
PCI hot plugging hardware but support USB hot plugging, including,
for example, almost all desktop PC's and typical "appliance" devices.
In addition, other places in the USB code have always relied on hot
plugging by simulating a disconnect and reconnect to recover from
some errors, a kludge which could potentially result in loss of some
device state, but which is too complex to fix before 2.4.0.

After 2.4.0, and after the fake disconnect/reconnect code in
drivers/usb/{devio,storage/scsiglue}.c is designed out, then we may
want to explore adding __usbdevinit{,data} defines in include/linux/init.h
that would be controlled by a new CONFIG_USB_HOTPLUG option, as in
the patches that I posted for this to linux-usb-devel.

In that case, CONFIG_USB_HOTPLUG=y would give you the current
behavior and CONFIG_USB_HOTPLUG=n would give you a slightly smaller kernel
that lacked the ability to support USB hot plugging. There is some
question as to whether CONFIG_USB_HOTPLUG=n would just be a cool hack
or if someone actually would use it. I am very interested in feeback
on this question.

Adam J. Richter __ ______________ 4880 Stevens Creek Blvd, Suite 104
[email protected] \ / San Jose, California 95129-1034
+1 408 261-6630 | g g d r a s i l United States of America
fax +1 408 261-6631 "Free Software For The Rest Of Us."


2000-11-15 06:00:32

by Jeff Garzik

[permalink] [raw]
Subject: Re: Patch(?): linux-2.4.0-test11-pre4/drivers/sound/yss225.c compilefailure

"Adam J. Richter" wrote:
> If a programmer errs in favor of __devinit, the result is
> extra memory consumption under CONFIG_HOTPLUG. If a programmer
> errs in favor of __init, the result is a crash during hot p
> ug insertion. Avoiding crashes at the expensive of a pretty small
> amount of memory usage is the more "conservative" way to err.

You suggest avoiding correctness in order to protect against dumb
programmers. That path leads to Windows.


> >Otherwise, you rob CONFIG_HOTPLUG people of some memory that could
> >otherwise be freed at boot. And the number of CONFIG_HOTPLUG people is
> >not small, it includes not only the CardBus users but USB users too...
>
> We have been discussing this on linux-devel-usb. The
> latest patches submitted to Linus and in 2.4.0-test10-pre{3,4}
> support USB hot plugging regardless of whether CONFIG_HOTPLUG is
> specified.
>
> bash% find linux-2.4.0-test11-pre4/drivers/usb -type f | xargs egrep HOTPLUG

Read the code. test11-pre[34] was broken due to my recent
CONFIG_KMOD/CONFIG_HOTPLUG separation, and should have had
CONFIG_HOTPLUG. test11-pre5 has CONFIG_HOTPLUG. As it should.


> Having USB hot plugging without needing to build in PCI
> hot plugging is useful,

Of course. But CONFIG_HOTPLUG does not mean PCI hotplugging. It means
any hotplug support in the kernel. That is why __devinit exists and is
used in a generic fashion.


> After 2.4.0, [...] we may
> want to explore adding __usbdevinit{,data} defines in include/linux/init.h
> that would be controlled by a new CONFIG_USB_HOTPLUG option, as in
> the patches that I posted for this to linux-usb-devel.

This is not just a USB issue. Please discuss this on linux-kernel, so
we can have a coherent hotplug strategy for the entire kernel.

If we are going to create CONFIG_USB_HOTPLUG, we must -eliminate-
CONFIG_HOTPLUG, and create CONFIG_PCI_HOTPLUG, and
CONFIG_ANOTHERBUS_HOTPLUG and so on, for each hotplug bus.

Jeff


--
Jeff Garzik |
Building 1024 | The chief enemy of creativity is "good" sense
MandrakeSoft | -- Picasso

2000-11-15 06:14:33

by Greg KH

[permalink] [raw]
Subject: Re: Patch(?): linux-2.4.0-test11-pre4/drivers/sound/yss225.c compilefailure

On Wed, Nov 15, 2000 at 12:29:15AM -0500, Jeff Garzik wrote:
>
> This is not just a USB issue. Please discuss this on linux-kernel, so
> we can have a coherent hotplug strategy for the entire kernel.

I agree. If I see the topic come up on linux-usb-devel again, I'll push
it over to linux-kernel.

> If we are going to create CONFIG_USB_HOTPLUG, we must -eliminate-
> CONFIG_HOTPLUG, and create CONFIG_PCI_HOTPLUG, and
> CONFIG_ANOTHERBUS_HOTPLUG and so on, for each hotplug bus.

Argh!
I thought the whole point of this was to make there be only one hotplug
strategy, due to the fact that this is a real need.

Please let's not go down this path. It was all starting to look so
nice...

greg k-h

--
[email protected](kroah|wirex).com
http://immunix.org/~greg

2000-11-15 06:25:06

by Jeff Garzik

[permalink] [raw]
Subject: Re: Patch(?): linux-2.4.0-test11-pre4/drivers/sound/yss225.c compilefailure

Greg KH wrote:
> On Wed, Nov 15, 2000 at 12:29:15AM -0500, Jeff Garzik wrote:
> > If we are going to create CONFIG_USB_HOTPLUG, we must -eliminate-
> > CONFIG_HOTPLUG, and create CONFIG_PCI_HOTPLUG, and
> > CONFIG_ANOTHERBUS_HOTPLUG and so on, for each hotplug bus.
>
> Argh!
> I thought the whole point of this was to make there be only one hotplug
> strategy, due to the fact that this is a real need.
>
> Please let's not go down this path. It was all starting to look so
> nice...

I -want- there to be only one hotplug strategy, but Adam seemed to be
talking about the opposite, with his CONFIG_USB_HOTPLUG suggestion.

I'm hoping that Linus will disagree with the splintering of
CONFIG_HOTPLUG too...

I think it's too late in 2.4.x cycle to change now anyway.

Jeff


--
Jeff Garzik |
Building 1024 | The chief enemy of creativity is "good" sense
MandrakeSoft | -- Picasso

2000-11-15 06:34:05

by Andre Hedrick

[permalink] [raw]
Subject: College of Cardinals Vote!!!

On Wed, 15 Nov 2000, Jeff Garzik wrote:

> I -want- there to be only one hotplug strategy, but Adam seemed to be
> talking about the opposite, with his CONFIG_USB_HOTPLUG suggestion.
>
> I'm hoping that Linus will disagree with the splintering of
> CONFIG_HOTPLUG too...

CONFIG_HOTPLUG CONFIG_'parse like hell'_HOTPLUG

2 0


2000-11-15 07:22:52

by Greg KH

[permalink] [raw]
Subject: Re: Patch(?): linux-2.4.0-test11-pre4/drivers/sound/yss225.c compilefailure

On Wed, Nov 15, 2000 at 12:54:35AM -0500, Jeff Garzik wrote:
>
> I -want- there to be only one hotplug strategy, but Adam seemed to be
> talking about the opposite, with his CONFIG_USB_HOTPLUG suggestion.

Here's Adam's proposal for CONFIG_USB_HOTPLUG:
http://www.geocrawler.com/lists/3/SourceForge/2571/250/4599696/

>From what I remember (and from looking at this message), all he seems to
want is to redefine the __init and __initdata macros depending on a
config item. There's no other grander scheme of things, right Adam?

Although such a small memory savings for turning a bus whose main goal
in life is to enable hot plugged devices into a fixed connection doesn't
seem worth it.

We are talking embedded USB hosts here, not devices. USB devices
running Linux is a whole 'nother thing, which I'm just now starting to
look into...

Comments Adam?

thanks,

greg k-h

--
[email protected](kroah|wirex).com
http://immunix.org/~greg