On Thu, Mar 31, 2011 at 11:23 PM, Wolfram Sang [off-list ref] wrote:

quoted

   Maybe I misunderstand you, in my view it is the responsibility of <vendor>
   to create their DTS files to indicate they want <special-card1> to bind to
   generic-uio.

Device tree is a OS-neutral hardware description language. "generic-uio"
is neither OS-neutral nor a hardware description. devicetree.org has
more information about this.

If we are trying to be pure, I might argue we are not changing the DTS
language, but rather just add support in Linux for a particular
use-case.  There is no violation of DTS syntax.

It might be *recommended* that device trees describe only hardware,
although as Michal points out there is already precedent in the
'chosen' node where this is clearly violated, but in a way that is
compatible with DTS syntax.

Is it forbidden to have DTS descriptions of purely virtual devices, as
would be present if you boot a DTS-driven kernel inside a VM
environment, which provides only virtual implementations of various
devices (ethernet etc)?

'vmware,virt-enet' or whatever?

quoted

   Our use-case is pretty clear, in FPGA-based systems it is common to create
   arbitrary devices that developers just want to control from userspace,
   with simple IRQ and IO capabilities (DMA can come later :). �They don't
   need to bind to other kernel APIs or subsystems, and don't want to invest
   in one-off kernel drivers that simply will never go upstream.

For that, the new_compatible-file would be suitable, I think.

# echo "generic-uio" > /sys/class/uio/<something>

?

quoted

   UIO is perfect, and simply tagging the device as generic-uio in the DTS is
   so simple, clean, and elegant.

Simple, yes (I do understand I wrote the first approach ;)) . Elegant,
not really, because it breaks core conventions of the device tree. For
your case it is a very conveniant hack, but it is still a hack.

Being useful seems like a high priority in the kernel, I'm not ashamed of it! :)

Regards,

John
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