* [PATCH RFC] uio: allow use on nommu systems
@ 2016-07-15 0:53 Rich Felker
2016-07-15 1:42 ` Greg Kroah-Hartman
0 siblings, 1 reply; 4+ messages in thread
From: Rich Felker @ 2016-07-15 0:53 UTC (permalink / raw)
To: Hans J. Koch, Greg Kroah-Hartman; +Cc: linux-kernel
mmap of uio devices does not seem to work without further
nommu-specific support, but interrupt handling already works, and
userspace drivers for nommu systems can simply use physical mmio
addresses from userspace directly anyway without mmap.
Signed-off-by: Rich Felker <dalias@libc.org>
---
I don't particularly expect this to be accepted upstream as-is, but
since we're actually trying to use the UIO subsystem on nommu (J2),
I'd like to start a discussion of what an acceptable patch would
entail.
The uio_pdrv_genirq driver was tested on J2 with this patch and
interrupt handling works as expected.
drivers/uio/Kconfig | 1 -
1 file changed, 1 deletion(-)
diff --git a/drivers/uio/Kconfig b/drivers/uio/Kconfig
index 52c98ce..387b2bb 100644
--- a/drivers/uio/Kconfig
+++ b/drivers/uio/Kconfig
@@ -1,6 +1,5 @@
menuconfig UIO
tristate "Userspace I/O drivers"
- depends on MMU
help
Enable this to allow the userspace driver core code to be
built. This code allows userspace programs easy access to
--
2.8.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH RFC] uio: allow use on nommu systems
2016-07-15 0:53 [PATCH RFC] uio: allow use on nommu systems Rich Felker
@ 2016-07-15 1:42 ` Greg Kroah-Hartman
2016-07-15 1:58 ` Rich Felker
0 siblings, 1 reply; 4+ messages in thread
From: Greg Kroah-Hartman @ 2016-07-15 1:42 UTC (permalink / raw)
To: Rich Felker; +Cc: Hans J. Koch, linux-kernel
On Thu, Jul 14, 2016 at 08:53:06PM -0400, Rich Felker wrote:
> mmap of uio devices does not seem to work without further
> nommu-specific support, but interrupt handling already works, and
> userspace drivers for nommu systems can simply use physical mmio
> addresses from userspace directly anyway without mmap.
>
> Signed-off-by: Rich Felker <dalias@libc.org>
> ---
>
> I don't particularly expect this to be accepted upstream as-is, but
> since we're actually trying to use the UIO subsystem on nommu (J2),
> I'd like to start a discussion of what an acceptable patch would
> entail.
>
> The uio_pdrv_genirq driver was tested on J2 with this patch and
> interrupt handling works as expected.
>
> drivers/uio/Kconfig | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/drivers/uio/Kconfig b/drivers/uio/Kconfig
> index 52c98ce..387b2bb 100644
> --- a/drivers/uio/Kconfig
> +++ b/drivers/uio/Kconfig
> @@ -1,6 +1,5 @@
> menuconfig UIO
> tristate "Userspace I/O drivers"
> - depends on MMU
This doesn't seem to do much, don't you need to modify uio-specific
drivers? Or given that the core uio code doesn't rely on mmu, is this
safe?
thanks,
greg k-h
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH RFC] uio: allow use on nommu systems
2016-07-15 1:42 ` Greg Kroah-Hartman
@ 2016-07-15 1:58 ` Rich Felker
2016-07-15 11:42 ` Greg Kroah-Hartman
0 siblings, 1 reply; 4+ messages in thread
From: Rich Felker @ 2016-07-15 1:58 UTC (permalink / raw)
To: Greg Kroah-Hartman; +Cc: Hans J. Koch, linux-kernel
On Fri, Jul 15, 2016 at 10:42:37AM +0900, Greg Kroah-Hartman wrote:
> On Thu, Jul 14, 2016 at 08:53:06PM -0400, Rich Felker wrote:
> > mmap of uio devices does not seem to work without further
> > nommu-specific support, but interrupt handling already works, and
> > userspace drivers for nommu systems can simply use physical mmio
> > addresses from userspace directly anyway without mmap.
> >
> > Signed-off-by: Rich Felker <dalias@libc.org>
> > ---
> >
> > I don't particularly expect this to be accepted upstream as-is, but
> > since we're actually trying to use the UIO subsystem on nommu (J2),
> > I'd like to start a discussion of what an acceptable patch would
> > entail.
> >
> > The uio_pdrv_genirq driver was tested on J2 with this patch and
> > interrupt handling works as expected.
> >
> > drivers/uio/Kconfig | 1 -
> > 1 file changed, 1 deletion(-)
> >
> > diff --git a/drivers/uio/Kconfig b/drivers/uio/Kconfig
> > index 52c98ce..387b2bb 100644
> > --- a/drivers/uio/Kconfig
> > +++ b/drivers/uio/Kconfig
> > @@ -1,6 +1,5 @@
> > menuconfig UIO
> > tristate "Userspace I/O drivers"
> > - depends on MMU
>
> This doesn't seem to do much, don't you need to modify uio-specific
> drivers? Or given that the core uio code doesn't rely on mmu, is this
> safe?
As noted above, mmap of the device does not work (returns error); I
don't understand why. But select/read/write for interrupt handling
works fine, and the uio system is fully usable if you just do mmio via
the raw addresses from userspace (this is nommu after all). I tested
it with uio_pdrv_genirq bound to a fake DT node for the J2 IPI
interrupt, disabling SMP and generating IPI interrupts manually to
check that it worked.
Rich
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH RFC] uio: allow use on nommu systems
2016-07-15 1:58 ` Rich Felker
@ 2016-07-15 11:42 ` Greg Kroah-Hartman
0 siblings, 0 replies; 4+ messages in thread
From: Greg Kroah-Hartman @ 2016-07-15 11:42 UTC (permalink / raw)
To: Rich Felker; +Cc: Hans J. Koch, linux-kernel
On Thu, Jul 14, 2016 at 09:58:29PM -0400, Rich Felker wrote:
> On Fri, Jul 15, 2016 at 10:42:37AM +0900, Greg Kroah-Hartman wrote:
> > On Thu, Jul 14, 2016 at 08:53:06PM -0400, Rich Felker wrote:
> > > mmap of uio devices does not seem to work without further
> > > nommu-specific support, but interrupt handling already works, and
> > > userspace drivers for nommu systems can simply use physical mmio
> > > addresses from userspace directly anyway without mmap.
> > >
> > > Signed-off-by: Rich Felker <dalias@libc.org>
> > > ---
> > >
> > > I don't particularly expect this to be accepted upstream as-is, but
> > > since we're actually trying to use the UIO subsystem on nommu (J2),
> > > I'd like to start a discussion of what an acceptable patch would
> > > entail.
> > >
> > > The uio_pdrv_genirq driver was tested on J2 with this patch and
> > > interrupt handling works as expected.
> > >
> > > drivers/uio/Kconfig | 1 -
> > > 1 file changed, 1 deletion(-)
> > >
> > > diff --git a/drivers/uio/Kconfig b/drivers/uio/Kconfig
> > > index 52c98ce..387b2bb 100644
> > > --- a/drivers/uio/Kconfig
> > > +++ b/drivers/uio/Kconfig
> > > @@ -1,6 +1,5 @@
> > > menuconfig UIO
> > > tristate "Userspace I/O drivers"
> > > - depends on MMU
> >
> > This doesn't seem to do much, don't you need to modify uio-specific
> > drivers? Or given that the core uio code doesn't rely on mmu, is this
> > safe?
>
> As noted above, mmap of the device does not work (returns error); I
> don't understand why.
Try working that out and then we can talk :)
thanks,
greg k-h
^ permalink raw reply [flat|nested] 4+ messages in thread
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2016-07-15 0:53 [PATCH RFC] uio: allow use on nommu systems Rich Felker
2016-07-15 1:42 ` Greg Kroah-Hartman
2016-07-15 1:58 ` Rich Felker
2016-07-15 11:42 ` Greg Kroah-Hartman
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