* Use of floating point in the kernel
@ 2004-01-07 23:59 Pekka Pietikainen
2004-01-08 3:34 ` H. Peter Anvin
0 siblings, 1 reply; 6+ messages in thread
From: Pekka Pietikainen @ 2004-01-07 23:59 UTC (permalink / raw)
To: linux-kernel; +Cc: linux-dvb
Hi
There are a few instances of use of floating point in 2.6,
--- linux-2.6.0-1.30/drivers/media/dvb/ttpci/av7110.c~ 2004-01-07 23:14:14.000000000 +0200
+++ linux-2.6.0-1.30/drivers/media/dvb/ttpci/av7110.c 2004-01-07 23:14:14.000000000 +0200
@@ -2673,9 +2673,9 @@
buf[1] = div & 0xff;
buf[2] = 0x8e;
- if (freq < (u32) 16*168.25 )
+ if (freq < 2692 ) /* 16*168.25 */
config = 0xa0;
- else if (freq < (u32) 16*447.25)
+ else if (freq < 7156) /* 16*447.25 */
config = 0x90;
else
config = 0x30;
(If I'm not mistaken a similar patch for this has already been sent to
Linus, just making sure the DVB people get this in their trees as well)
(u32) (16*168.25) would work too, I suppose.
The other case is a bit more widespread, patch below is mostly rhetoric :-)
http://www.winischhofer.net/linuxsisvga.shtml#download contains the latest version
of the sisfb that doesn't use floating point at all, so that is certainly the better
option.
--- linux-2.6.0-1.30/drivers/video/sis/sis_main.c~ 2004-01-08 01:27:44.909006216 +0200
+++ linux-2.6.0-1.30/drivers/video/sis/sis_main.c 2004-01-08 01:28:19.111806600 +0200
@@ -616,6 +616,7 @@
var->left_margin + var->xres + var->right_margin +
var->hsync_len;
unsigned int vtotal = 0;
+#error Use of floating point in the kernel is NOT safe!
double drate = 0, hrate = 0;
int found_mode = 0;
int old_mode;
--- linux-2.6.0-1.30/drivers/video/Kconfig~ 2004-01-08 01:25:37.570364632 +0200
+++ linux-2.6.0-1.30/drivers/video/Kconfig 2004-01-08 01:25:37.571364480 +0200
@@ -704,7 +704,7 @@
config FB_SIS
tristate "SIS acceleration"
- depends on FB && PCI
+ depends on FB && PCI && BROKEN
help
This is the frame buffer device driver for the SiS 630 and 640 Super
Socket 7 UMA cards. Specs available at <http://www.sis.com.tw/>.
--
Pekka Pietikainen
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Use of floating point in the kernel
2004-01-07 23:59 Use of floating point in the kernel Pekka Pietikainen
@ 2004-01-08 3:34 ` H. Peter Anvin
2004-01-08 3:48 ` Dave Jones
2004-01-08 3:52 ` Linus Torvalds
0 siblings, 2 replies; 6+ messages in thread
From: H. Peter Anvin @ 2004-01-08 3:34 UTC (permalink / raw)
To: linux-kernel
Pekka Pietikainen wrote:
> Hi
>
> There are a few instances of use of floating point in 2.6,
>
Has anyone considered asking the gcc people to add an -fno-fpu (or
-mno-fpu) option, throwing an error if any FP instructions are used?
-hpa
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Use of floating point in the kernel
2004-01-08 3:34 ` H. Peter Anvin
@ 2004-01-08 3:48 ` Dave Jones
2004-01-08 3:52 ` Linus Torvalds
1 sibling, 0 replies; 6+ messages in thread
From: Dave Jones @ 2004-01-08 3:48 UTC (permalink / raw)
To: H. Peter Anvin; +Cc: linux-kernel
On Wed, Jan 07, 2004 at 07:34:06PM -0800, H. Peter Anvin wrote:
> Has anyone considered asking the gcc people to add an -fno-fpu (or
> -mno-fpu) option, throwing an error if any FP instructions are used?
building with -msoft-float gets you this.
Dave
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Use of floating point in the kernel
2004-01-08 3:34 ` H. Peter Anvin
2004-01-08 3:48 ` Dave Jones
@ 2004-01-08 3:52 ` Linus Torvalds
2004-01-08 3:54 ` H. Peter Anvin
1 sibling, 1 reply; 6+ messages in thread
From: Linus Torvalds @ 2004-01-08 3:52 UTC (permalink / raw)
To: H. Peter Anvin; +Cc: linux-kernel
On Wed, 7 Jan 2004, H. Peter Anvin wrote:
>
> Pekka Pietikainen wrote:
> >
> > There are a few instances of use of floating point in 2.6,
>
> Has anyone considered asking the gcc people to add an -fno-fpu (or
> -mno-fpu) option, throwing an error if any FP instructions are used?
We really should, but there really are some rare cases where it is
actually ok.
In particular, you _can_ do math, if you just do the proper
"kernel_fpu_begin()"/"kernel_fpu_end()" around it, and you have reason to
believe that you can assume a math processor exists.
Is it needed? I dunno. I'd frown on it in general, but I don't see it
being fundamentally wrong under the rigth circumstances.
Linus
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Use of floating point in the kernel
2004-01-08 3:52 ` Linus Torvalds
@ 2004-01-08 3:54 ` H. Peter Anvin
0 siblings, 0 replies; 6+ messages in thread
From: H. Peter Anvin @ 2004-01-08 3:54 UTC (permalink / raw)
To: Linus Torvalds; +Cc: linux-kernel
Linus Torvalds wrote:
>
> We really should, but there really are some rare cases where it is
> actually ok.
>
> In particular, you _can_ do math, if you just do the proper
> "kernel_fpu_begin()"/"kernel_fpu_end()" around it, and you have reason to
> believe that you can assume a math processor exists.
>
> Is it needed? I dunno. I'd frown on it in general, but I don't see it
> being fundamentally wrong under the rigth circumstances.
>
Sure; however, perhaps those can be marked separately in the Makefile.
-hpa
^ permalink raw reply [flat|nested] 6+ messages in thread
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2004-01-07 23:59 Use of floating point in the kernel Pekka Pietikainen
2004-01-08 3:34 ` H. Peter Anvin
2004-01-08 3:48 ` Dave Jones
2004-01-08 3:52 ` Linus Torvalds
2004-01-08 3:54 ` H. Peter Anvin
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2004-01-08 4:12 ` Andi Kleen
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