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* Patch(?): linux-2.4.0-test11-pre4/drivers/sound/yss225.c compile failure
@ 2000-11-13 22:44 Adam J. Richter
  2000-11-14 22:56 ` Bartlomiej Zolnierkiewicz
  0 siblings, 1 reply; 11+ messages in thread
From: Adam J. Richter @ 2000-11-13 22:44 UTC (permalink / raw)
  To: bkz; +Cc: linux-kernel




	linux-2.4.0-test11-pre4/drivers/sound/yss225.c uses __initdata
but does not include <linux/init.h>, so it could not compile.  I have
attached below.

	Note that I am a bit uncertain about the correctness of
the __initdata prefix here in the first place.  Is yss225 a PCI
device?  If so, a kernel that supports PCI hot plugging should
be prepared to support the possibility of a hot pluggable yss225
card being inserted after the module has already been initialized.
Even if no CardBus or CompactPCI version of yss225 hardware exists
yet, it will require less maintenance for PCI drivers to be prepared
for this possibility from the outset (besides, is it possible to have a
hot pluggable PCI bridge card that bridges to a regular PCI bus?).

	So, if yss225 is a PCI device, the declaration should use
__devinitdata.  On the other hand, if it is ISA only, then __initdata
should be correct.

Adam J. Richter     __     ______________   4880 Stevens Creek Blvd, Suite 104
adam@yggdrasil.com     \ /                  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."

--- linux-2.4.0-test11-pre4/drivers/sound/yss225.c	Mon Nov 13 13:36:50 2000
+++ linux/drivers/sound/yss225.c	Mon Nov 13 09:11:02 2000
@@ -1,3 +1,4 @@
+#include <linux/init.h>
 unsigned char page_zero[] __initdata = {
 0x01, 0x7c, 0x00, 0x1e, 0x00, 0x00, 0x00, 0x00, 0x00, 0xf5, 0x00,
 0x11, 0x00, 0x20, 0x00, 0x32, 0x00, 0x40, 0x00, 0x13, 0x00, 0x00,
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^ permalink raw reply	[flat|nested] 11+ messages in thread
* Re: Patch(?): linux-2.4.0-test11-pre4/drivers/sound/yss225.c compilefailure
@ 2000-11-15  1:02 Adam J. Richter
  2000-11-15  5:29 ` Jeff Garzik
  0 siblings, 1 reply; 11+ messages in thread
From: Adam J. Richter @ 2000-11-15  1:02 UTC (permalink / raw)
  To: dake, jgarzik, linux-kernel

	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
adam@yggdrasil.com     \ /                  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."
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^ permalink raw reply	[flat|nested] 11+ messages in thread
* Re: Patch(?): linux-2.4.0-test11-pre4/drivers/sound/yss225.c compilefailure
@ 2000-11-15  7:58 Adam J. Richter
  0 siblings, 0 replies; 11+ messages in thread
From: Adam J. Richter @ 2000-11-15  7:58 UTC (permalink / raw)
  To: jgarzik; +Cc: linux-kernel

Jeff Garzik wrote:
>"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.

	No, I was saying that if you are unsure whether to use
__devinit{,data} or __init{,data}, using __dev version more closely
fulfulls your request that we "Please err on the conservative side."

	 If you are sure of the correct one to use, then, of
course, I am sure we all agree you should use it.

>>         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.

	Could you please cite an example or two of where __devinit
is currently correctly used for a non-PCI non-USB device?  I think you
can skip the places in the ISA parallel port code where it is apparently
being incorrectly used (where some non-hot-pluggable ISA code that could
safely be freed will be retained if the kernel is compied with
CONFIG_HOTPLUG).

	Earlier in your email, you made an argument about the
development culture ("That path leads to Windows").  In that
same spirit, let's not rely on bureaucratic doctrines like "But
CONFIG_HOTPLUG does not mean..." and, instead, let's look at
the underlying technical issues, which I believe are:

	       1. there is essentially no call graph dependency between
		  the hot plugging mechanisms of different busses,

	       2. we agree that having USB hot plugging without needing
		  to build in PCI hot plugging is useful.

>>         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.

	s/must/should/  (since you are not changing the resulting binary)

	I agree that CONFIG_HOTPLUG should be renamed CONFIG_PCI_HOTPLUG
and I would further like to see __devinit{,data} become __pcidevinit{,data}.
Not only does this configurability have real world uses, but the clearer
labelling would also make the effected code a little more self documenting
as to why the code and data in question is not just __init{,data}.

Adam J. Richter     __     ______________   4880 Stevens Creek Blvd, Suite 104
adam@yggdrasil.com     \ /                  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."
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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^ permalink raw reply	[flat|nested] 11+ messages in thread
* Re: Patch(?): linux-2.4.0-test11-pre4/drivers/sound/yss225.c compilefailure
@ 2000-11-15  8:32 Adam J. Richter
  0 siblings, 0 replies; 11+ messages in thread
From: Adam J. Richter @ 2000-11-15  8:32 UTC (permalink / raw)
  To: greg; +Cc: linux-kernel

>  = Greg KH
>> = Jeff Garzik


>> 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/

Thanks, Greg!


>>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?

	Yes, I would have __usbdev{init,exit}{,data} be defined based
on CONFIG_USB_HOTPLUG.

>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.
[...]
>Comments Adam?

	There would be more memory savings from tagging all USB
device driver initialization and exit routines with __usbdevinit
and __usbdevexit.

	Although hot plugging is a convenient feature of USB, there 
are plenty of applications of USB that do not use hot plugging.  For
example, imagine some kind of kiosk or internet appliciance that
uses a USB keyboard or camera, because that is the commodity hardware,
but which the user is not able to physically unplug.   Perhaps this
embedded would get cost benefits from a smaller kernel.  That is the
sort of potential use that I can imagine for "CONFIG_USB_HOTPLUG=n".
As I said, I am interested in feedback from potential users of
CONFIG_USB_HOTPLUG=n to determine if anyone would use it or if
it is just an intellectual exercise.

	The part that is more clearly useful is being able to have USB
hot plugging without compiling in PCI hot plugging.  So, CONFIG_HOTPLUG
be CONFIG_PCI_HOTPLUG, or at least should be thought of that way,
regardless of whether CONFIG_USB_HOTPLUG is added.

Adam J. Richter     __     ______________   4880 Stevens Creek Blvd, Suite 104
adam@yggdrasil.com     \ /                  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."
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
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^ permalink raw reply	[flat|nested] 11+ messages in thread
end of thread, other threads:[~2000-11-15  9:03 UTC | newest]

Thread overview: 11+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2000-11-13 22:44 Patch(?): linux-2.4.0-test11-pre4/drivers/sound/yss225.c compile failure Adam J. Richter
2000-11-14 22:56 ` Bartlomiej Zolnierkiewicz
2000-11-14 23:01   ` Patch(?): linux-2.4.0-test11-pre4/drivers/sound/yss225.c compilefailure Jeff Garzik
2000-11-14 23:17     ` Bartlomiej Zolnierkiewicz
  -- strict thread matches above, loose matches on Subject: below --
2000-11-15  1:02 Adam J. Richter
2000-11-15  5:29 ` Jeff Garzik
2000-11-15  5:43   ` Greg KH
2000-11-15  5:54     ` Jeff Garzik
2000-11-15  6:52       ` Greg KH
2000-11-15  7:58 Adam J. Richter
2000-11-15  8:32 Adam J. Richter

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