1 // SPDX-License-Identifier: GPL-2.0-only
6  * Simple descriptor-based ring. virtio 0.9 compatible event index is used for
15 /* Next - Where next entry will be written.
16  * Prev - "Next" value when event triggered previously.
17  * Event - Peer requested event after writing this entry.
23 	return (unsigned short)(next - event - 1) < (unsigned short)(next - prev);  in need_event()
27  * Guest adds descriptors with unique index values and DESC_HW in flags.
46 	unsigned char reserved0[HOST_GUEST_PADDING - 2];
48 	unsigned char reserved1[HOST_GUEST_PADDING - 2];
59 struct guest {  struct
64 	unsigned char reserved[HOST_GUEST_PADDING - 12];
65 } guest;  argument
73 	unsigned char reserved[HOST_GUEST_PADDING - 4];
92 	guest.avail_idx = 0;  in alloc_ring()
93 	guest.kicked_avail_idx = -1;  in alloc_ring()
94 	guest.last_used_idx = 0;  in alloc_ring()
96 	host.called_used_idx = -1;  in alloc_ring()
103 	guest.num_free = ring_size;  in alloc_ring()
111 /* guest side */
116 	if (!guest.num_free)  in add_inbuf()
117 		return -1;  in add_inbuf()
119 	guest.num_free--;  in add_inbuf()
120 	head = (ring_size - 1) & (guest.avail_idx++);  in add_inbuf()
145 	unsigned head = (ring_size - 1) & guest.last_used_idx;  in get_buf()
154 	index = ring[head].index & (ring_size - 1);  in get_buf()
159 	guest.num_free++;  in get_buf()
160 	guest.last_used_idx++;  in get_buf()
166 	unsigned head = (ring_size - 1) & guest.last_used_idx;  in used_empty()
180 	event->call_index = guest.last_used_idx;  in enable_call()
194 	need = need_event(event->kick_index,  in kick_available()
195 			   guest.avail_idx,  in kick_available()
196 			   guest.kicked_avail_idx);  in kick_available()
198 	guest.kicked_avail_idx = guest.avail_idx;  in kick_available()
203 /* host side */
213 	event->kick_index = host.used_idx;  in enable_kick()
221 	unsigned head = (ring_size - 1) & host.used_idx;  in avail_empty()
228 	unsigned head = (ring_size - 1) & host.used_idx;  in use_buf()
237 	/* simple in-order completion: we don't need  in use_buf()
239 	 * can just modify the descriptor in-place.  in use_buf()
241 	ring[head].len--;  in use_buf()
243 	 * Note: alternative is to write len and flags in one access -  in use_buf()
262 	need = need_event(event->call_index,  in call_used()