linux-kernel - Re: [PATCH RFC] uio: allow use on nommu systems

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Date:	Fri, 15 Jul 2016 20:42:54 +0900
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Rich Felker <dalias@...c.org>
Cc:	"Hans J. Koch" <hjk@...sjkoch.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] uio: allow use on nommu systems

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@...c.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