Patchwork pata_of_platform: fix no irq handling

login
register
mail settings
Submitter Anton Vorontsov
Date Oct. 6, 2008, 5:26 p.m.
Message ID <20081006172653.GA26427@oksana.dev.rtsoft.ru>
Download mbox | patch
Permalink /patch/2938/
State Accepted
Headers show

Comments

Anton Vorontsov - Oct. 6, 2008, 5:26 p.m.
When no irq specified the pata_of_platform fills the irq_res with -1,
which is wrong to do for two reasons:

1. By definition, 'no irq' should be IRQ 0, not some negative integer;
2. pata_platform checks for irq_res.start > 0, but since irq_res.start
   is unsigned type, the check will be true for `-1'.

Reported-by: Steven A. Falco <sfalco@harris.com>
Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
---

Resending again...

 drivers/ata/pata_of_platform.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
Matt Sealey - Oct. 6, 2008, 8:41 p.m.
There is a simple problem with the patch which is that an "IRQ 0" can and does
actually exist on a bunch of platforms, at least to the best of my knowledge.

Checking for -1 (which means for definite, no irq at all, because it is
totally unambiguous, as a -1 IRQ numbering is "impossible") is more correct.

The problem is the check against an unsigned value for interrupts (is there
any reason why you would need 4 billion interrupts possible instead of just
2 billion?) although I must say, the patch will work, and probably 99.9999999%
of people will never see a problem with it :)
Anton Vorontsov - Oct. 6, 2008, 9:32 p.m.
On Mon, Oct 06, 2008 at 03:41:19PM -0500, Matt Sealey wrote:
> There is a simple problem with the patch which is that an "IRQ 0" can and does
> actually exist on a bunch of platforms, at least to the best of my knowledge.
> 
> Checking for -1 (which means for definite, no irq at all, because it is
> totally unambiguous, as a -1 IRQ numbering is "impossible") is more correct.

This was discussed years ago.

http://lkml.org/lkml/2005/11/22/159
http://lkml.org/lkml/2005/11/22/227
Tejun Heo - Oct. 7, 2008, 1:30 a.m.
Anton Vorontsov wrote:
> On Mon, Oct 06, 2008 at 03:41:19PM -0500, Matt Sealey wrote:
>> There is a simple problem with the patch which is that an "IRQ 0" can and does
>> actually exist on a bunch of platforms, at least to the best of my knowledge.
>>
>> Checking for -1 (which means for definite, no irq at all, because it is
>> totally unambiguous, as a -1 IRQ numbering is "impossible") is more correct.
> 
> This was discussed years ago.
> 
> http://lkml.org/lkml/2005/11/22/159
> http://lkml.org/lkml/2005/11/22/227
> 

Would this break any existing platforms?  If so, can those be fixed
together or does it become a much bigger problem that way?

Thanks.
Wang Jian - Oct. 7, 2008, 9:18 a.m.
Tejun Heo wrote:
> Anton Vorontsov wrote:
>> On Mon, Oct 06, 2008 at 03:41:19PM -0500, Matt Sealey wrote:
>>> There is a simple problem with the patch which is that an "IRQ 0" can and does
>>> actually exist on a bunch of platforms, at least to the best of my knowledge.
>>>
>>> Checking for -1 (which means for definite, no irq at all, because it is
>>> totally unambiguous, as a -1 IRQ numbering is "impossible") is more correct.
>> This was discussed years ago.
>>
>> http://lkml.org/lkml/2005/11/22/159
>> http://lkml.org/lkml/2005/11/22/227
>>
> 
> Would this break any existing platforms?  If so, can those be fixed
> together or does it become a much bigger problem that way?
> 

Pata_of_platform stacks upon pata_platform. This patch fixes problem
concerning definition of "no irq" without touch any other place.  So
far I can't see any new problem.
Anton Vorontsov - Oct. 7, 2008, 9:26 a.m.
On Tue, Oct 07, 2008 at 10:30:59AM +0900, Tejun Heo wrote:
> Anton Vorontsov wrote:
> > On Mon, Oct 06, 2008 at 03:41:19PM -0500, Matt Sealey wrote:
> >> There is a simple problem with the patch which is that an "IRQ 0" can and does
> >> actually exist on a bunch of platforms, at least to the best of my knowledge.
> >>
> >> Checking for -1 (which means for definite, no irq at all, because it is
> >> totally unambiguous, as a -1 IRQ numbering is "impossible") is more correct.
> > 
> > This was discussed years ago.
> > 
> > http://lkml.org/lkml/2005/11/22/159
> > http://lkml.org/lkml/2005/11/22/227
> > 
> 
> Would this break any existing platforms?

Nope.

The driver is only available for PPC platforms.

As time goes by one can change `depend on PPC_OF' to just `depends on
OF', so that the driver will be also available for SPARC. And still
it will work, because SPARC also understands VIRQ0 as invalid VIRQ.


Thanks,
Alan Cox - Oct. 7, 2008, 9:37 a.m.
> > This was discussed years ago.
> > 
> > http://lkml.org/lkml/2005/11/22/159
> > http://lkml.org/lkml/2005/11/22/227
> > 
> 
> Would this break any existing platforms?  If so, can those be fixed
> together or does it become a much bigger problem that way?

Zero means no IRQ. Any platform with bits of code left over exposing IRQ
0 is already not supported by lots of driver code including libata.

As IRQs are unsigned using -1 is asking for trouble
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/
Benjamin Herrenschmidt - Oct. 7, 2008, 10:04 a.m.
On Tue, 2008-10-07 at 13:26 +0400, Anton Vorontsov wrote:
> On Tue, Oct 07, 2008 at 10:30:59AM +0900, Tejun Heo wrote:
> > Anton Vorontsov wrote:
> > > On Mon, Oct 06, 2008 at 03:41:19PM -0500, Matt Sealey wrote:
> > >> There is a simple problem with the patch which is that an "IRQ 0" can and does
> > >> actually exist on a bunch of platforms, at least to the best of my knowledge.
> > >>
> > >> Checking for -1 (which means for definite, no irq at all, because it is
> > >> totally unambiguous, as a -1 IRQ numbering is "impossible") is more correct.
> > > 
> > > This was discussed years ago.
> > > 
> > > http://lkml.org/lkml/2005/11/22/159
> > > http://lkml.org/lkml/2005/11/22/227
> > > 
> > 
> > Would this break any existing platforms?
> 
> Nope.
> 
> The driver is only available for PPC platforms.
> 
> As time goes by one can change `depend on PPC_OF' to just `depends on
> OF', so that the driver will be also available for SPARC. And still
> it will work, because SPARC also understands VIRQ0 as invalid VIRQ.
> 

Yup, I agree. I'll pick it up in my next batch.

Cheers,
Ben.
David Woodhouse - Oct. 8, 2008, 8:40 a.m.
On Tue, 2008-10-07 at 10:37 +0100, Alan Cox wrote:
> Zero means no IRQ. Any platform with bits of code left over exposing IRQ
> 0 is already not supported by lots of driver code including libata.

...and must implement some kind of interrupt remapping crap just to work
around this bogus design decision.
Alan Cox - Oct. 8, 2008, 9 a.m.
On Wed, 08 Oct 2008 09:40:54 +0100
David Woodhouse <dwmw2@infradead.org> wrote:

> On Tue, 2008-10-07 at 10:37 +0100, Alan Cox wrote:
> > Zero means no IRQ. Any platform with bits of code left over exposing IRQ
> > 0 is already not supported by lots of driver code including libata.
> 
> ...and must implement some kind of interrupt remapping crap just to work
> around this bogus design decision.

I'll leave you to argue with Linus about that, but since that was the
decision back in 2005 (for good C reasons) we can safely rely on it.
Geert Uytterhoeven - Oct. 8, 2008, 9:59 a.m.
On Wed, 8 Oct 2008, Alan Cox wrote:
> On Wed, 08 Oct 2008 09:40:54 +0100
> David Woodhouse <dwmw2@infradead.org> wrote:
> 
> > On Tue, 2008-10-07 at 10:37 +0100, Alan Cox wrote:
> > > Zero means no IRQ. Any platform with bits of code left over exposing IRQ
> > > 0 is already not supported by lots of driver code including libata.
> > 
> > ...and must implement some kind of interrupt remapping crap just to work
> > around this bogus design decision.
> 
> I'll leave you to argue with Linus about that, but since that was the
> decision back in 2005 (for good C reasons) we can safely rely on it.

`git grep NO_IRQ include arch/*/include' is still quite enlightening...

With kind regards,

Geert Uytterhoeven
Software Architect

Sony Techsoft Centre Europe
The Corporate Village · Da Vincilaan 7-D1 · B-1935 Zaventem · Belgium

Phone:    +32 (0)2 700 8453
Fax:      +32 (0)2 700 8622
E-mail:   Geert.Uytterhoeven@sonycom.com
Internet: http://www.sony-europe.com/

A division of Sony Europe (Belgium) N.V.
VAT BE 0413.825.160 · RPR Brussels
Fortis · BIC GEBABEBB · IBAN BE41293037680010
Alan Cox - Oct. 8, 2008, 10:27 a.m.
> > I'll leave you to argue with Linus about that, but since that was the
> > decision back in 2005 (for good C reasons) we can safely rely on it.
> 
> `git grep NO_IRQ include arch/*/include' is still quite enlightening...

Good guide to platform code we should delete really
Paul Mundt - Oct. 10, 2008, 5:55 p.m.
On Wed, Oct 08, 2008 at 11:59:59AM +0200, Geert Uytterhoeven wrote:
> On Wed, 8 Oct 2008, Alan Cox wrote:
> > On Wed, 08 Oct 2008 09:40:54 +0100
> > David Woodhouse <dwmw2@infradead.org> wrote:
> > 
> > > On Tue, 2008-10-07 at 10:37 +0100, Alan Cox wrote:
> > > > Zero means no IRQ. Any platform with bits of code left over exposing IRQ
> > > > 0 is already not supported by lots of driver code including libata.
> > > 
> > > ...and must implement some kind of interrupt remapping crap just to work
> > > around this bogus design decision.
> > 
> > I'll leave you to argue with Linus about that, but since that was the
> > decision back in 2005 (for good C reasons) we can safely rely on it.
> 
> `git grep NO_IRQ include arch/*/include' is still quite enlightening...
> 
In the case of PCI where IRQ is unsigned int, that's certainly bogus. The
problem originates on platforms where a 1:1 mapping between vector and
IRQ exists, where 0 is a valid value. This then needs to be remapped in
to an IRQ cookie that has a non-0 value in order to be assigned to
dev->irq. Despite whether this is bogus or not, there's not much to be
done about it. Those of us with vectored IRQ platforms generally have
enough sources that the use of IRQ-0 doesn't matter, and it's not worth
the headache of setting up the remapping crap.

As an example, on SH, IRQ-0 is mapped to vector 0x200. It is '0' for
symbolic reasons only. It's just as easy to pad out irq_desc and treat it
as an off-by-1 to work around all of code that assumes NO_IRQ == 0. There
is enough code in the kernel today that makes the non-zero IRQ cookie
assumption that platforms that do otherwise are simply broken.
Tejun Heo - Oct. 13, 2008, 6:56 a.m.
Anton Vorontsov wrote:
> When no irq specified the pata_of_platform fills the irq_res with -1,
> which is wrong to do for two reasons:
> 
> 1. By definition, 'no irq' should be IRQ 0, not some negative integer;
> 2. pata_platform checks for irq_res.start > 0, but since irq_res.start
>    is unsigned type, the check will be true for `-1'.
> 
> Reported-by: Steven A. Falco <sfalco@harris.com>
> Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>

applied to #tj-upstream (will soon be sent upstream)
Jeff Garzik - Oct. 13, 2008, 1:27 p.m.
Tejun Heo wrote:
> Anton Vorontsov wrote:
>> When no irq specified the pata_of_platform fills the irq_res with -1,
>> which is wrong to do for two reasons:
>>
>> 1. By definition, 'no irq' should be IRQ 0, not some negative integer;
>> 2. pata_platform checks for irq_res.start > 0, but since irq_res.start
>>    is unsigned type, the check will be true for `-1'.
>>
>> Reported-by: Steven A. Falco <sfalco@harris.com>
>> Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
> 
> applied to #tj-upstream (will soon be sent upstream)

I have returned!  muhahahahahaha....


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/
Tejun Heo - Oct. 13, 2008, 1:53 p.m.
Jeff Garzik wrote:
> Tejun Heo wrote:
>> Anton Vorontsov wrote:
>>> When no irq specified the pata_of_platform fills the irq_res with -1,
>>> which is wrong to do for two reasons:
>>>
>>> 1. By definition, 'no irq' should be IRQ 0, not some negative integer;
>>> 2. pata_platform checks for irq_res.start > 0, but since irq_res.start
>>>    is unsigned type, the check will be true for `-1'.
>>>
>>> Reported-by: Steven A. Falco <sfalco@harris.com>
>>> Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
>>
>> applied to #tj-upstream (will soon be sent upstream)
> 
> I have returned!  muhahahahahaha....

Ah.. great.  Hope you enjoyed the vacation.  Can you please pull from
#tj-upstream?

 git://git.kernel.org/pub/scm/linux/kernel/git/tj/libata-dev.git tj-upstream
 http://git.kernel.org/?p=linux/kernel/git/tj/libata-dev.git;a=shortlog;h=tj-upstream

Nothing much.  Rafael's skip-spin-off patchset + Elias's small fix +
ATA_HORKAGE_ATAPI_MOD16_DMA + pata_of_platform irq fix.

Gwendal posted patches to enable FIS based switching when NCQ is
disabled on sata_mv but I think this should be put into separate
branch and stay in linux-next till Mark Lord comes back and reviews it
as I don't know much about the driver and don't know of anyone other
than Gwendal and Mark who do.

sata_nv detection problem is still not resolved.  I figured out
generic and ck804 but nf2/3 is still malfunctioning.  I asked for more
tests and am waiting for results.

Eh... I guess that's about it.  Enjoy your INBOX.  :-P
Benjamin Herrenschmidt - Oct. 13, 2008, 11:27 p.m.
On Mon, 2008-10-13 at 15:56 +0900, Tejun Heo wrote:
> Anton Vorontsov wrote:
> > When no irq specified the pata_of_platform fills the irq_res with -1,
> > which is wrong to do for two reasons:
> > 
> > 1. By definition, 'no irq' should be IRQ 0, not some negative integer;
> > 2. pata_platform checks for irq_res.start > 0, but since irq_res.start
> >    is unsigned type, the check will be true for `-1'.
> > 
> > Reported-by: Steven A. Falco <sfalco@harris.com>
> > Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
> 
> applied to #tj-upstream (will soon be sent upstream)

Hrm... I applied it to powerpc.git too :-) Hopefully the merge will sort
it out !

Cheers,
Ben.

Patch

diff --git a/drivers/ata/pata_of_platform.c b/drivers/ata/pata_of_platform.c
index 408da30..1f18ad9 100644
--- a/drivers/ata/pata_of_platform.c
+++ b/drivers/ata/pata_of_platform.c
@@ -52,7 +52,7 @@  static int __devinit pata_of_platform_probe(struct of_device *ofdev,
 
 	ret = of_irq_to_resource(dn, 0, &irq_res);
 	if (ret == NO_IRQ)
-		irq_res.start = irq_res.end = -1;
+		irq_res.start = irq_res.end = 0;
 	else
 		irq_res.flags = 0;