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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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