hw: misc, add educational driver

I am using qemu for teaching the Linux kernel at our university. I
wrote a simple PCI device that can answer to writes/reads, generate
interrupts and perform DMA. As I am dragging it locally over 2 years,
I am sending it to you now.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
[Fix 32-bit compilation. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

docs/specs/edu.txt

@@ -0,0 +1,110 @@
+
+EDU device
+==========
+
+Copyright (c) 2014-2015 Jiri Slaby
+
+This document is licensed under the GPLv2 (or later).
+
+This is an educational device for writing (kernel) drivers. Its original
+intention was to support the Linux kernel lectures taught at the Masaryk
+University. Students are given this virtual device and are expected to write a
+driver with I/Os, IRQs, DMAs and such.
+
+The devices behaves very similar to the PCI bridge present in the COMBO6 cards
+developed under the Liberouter wings. Both PCI device ID and PCI space is
+inherited from that device.
+
+Command line switches:
+    -device edu[,dma_mask=mask]
+
+    dma_mask makes the virtual device work with DMA addresses with the given
+    mask. For educational purposes, the device supports only 28 bits (256 MiB)
+    by default. Students shall set dma_mask for the device in the OS driver
+    properly.
+
+PCI specs
+---------
+
+PCI ID: 1234:11e8
+
+PCI Region 0:
+   I/O memory, 1 MB in size. Users are supposed to communicate with the card
+   through this memory.
+
+MMIO area spec
+--------------
+
+Only size == 4 accesses are allowed for addresses < 0x80. size == 4 or
+size == 8 for the rest.
+
+0x00 (RO) : identification (0xRRrr00edu)
+	    RR -- major version
+	    rr -- minor version
+
+0x04 (RW) : card liveness check
+	    It is a simple value inversion (~ C operator).
+
+0x08 (RW) : factorial computation
+	    The stored value is taken and factorial of it is put back here.
+	    This happens only after factorial bit in the status register (0x20
+	    below) is cleared.
+
+0x20 (RW) : status register, bitwise OR
+	    0x01 -- computing factorial (RO)
+	    0x80 -- raise interrupt 0x01 after finishing factorial computation
+
+0x24 (RO) : interrupt status register
+	    It contains values which raised the interrupt (see interrupt raise
+	    register below).
+
+0x60 (WO) : interrupt raise register
+	    Raise an interrupt. The value will be put to the interrupt status
+	    register (using bitwise OR).
+
+0x64 (WO) : interrupt acknowledge register
+	    Clear an interrupt. The value will be cleared from the interrupt
+	    status register. This needs to be done from the ISR to stop
+	    generating interrupts.
+
+0x80 (RW) : DMA source address
+	    Where to perform the DMA from.
+
+0x88 (RW) : DMA destination address
+	    Where to perform the DMA to.
+
+0x90 (RW) : DMA transfer count
+	    The size of the area to perform the DMA on.
+
+0x98 (RW) : DMA command register, bitwise OR
+	    0x01 -- start transfer
+	    0x02 -- direction (0: from RAM to EDU, 1: from EDU to RAM)
+	    0x04 -- raise interrupt 0x100 after finishing the DMA
+
+IRQ controller
+--------------
+An IRQ is generated when written to the interrupt raise register. The value
+appears in interrupt status register when the interrupt is raised and has to
+be written to the interrupt acknowledge register to lower it.
+
+DMA controller
+--------------
+One has to specify, source, destination, size, and start the transfer. One
+4096 bytes long buffer at offset 0x40000 is available in the EDU device. I.e.
+one can perform DMA to/from this space when programmed properly.
+
+Example of transferring a 100 byte block to and from the buffer using a given
+PCI address 'addr':
+addr     -> DMA source address
+0x40000  -> DMA destination address
+100      -> DMA transfer count
+1        -> DMA command register
+while (DMA command register & 1)
+	;
+
+0x40000  -> DMA source address
+addr+100 -> DMA destination address
+100      -> DMA transfer count
+3        -> DMA command register
+while (DMA command register & 1)
+	;