xref: /linux/drivers/tty/hvc/hvsi_lib.c (revision 498495dba268b20e8eadd7fe93c140c68b6cc9d2)

// SPDX-License-Identifier: GPL-2.0
#include <linux/types.h>
#include <linux/delay.h>
#include <linux/slab.h>
#include <linux/console.h>
#include <asm/hvsi.h>

#include "hvc_console.h"

static int hvsi_send_packet(struct hvsi_priv *pv, struct hvsi_header *packet)
{
	packet->seqno = cpu_to_be16(atomic_inc_return(&pv->seqno));

	/* Assumes that always succeeds, works in practice */
	return pv->put_chars(pv->termno, (char *)packet, packet->len);
}

static void hvsi_start_handshake(struct hvsi_priv *pv)
{
	struct hvsi_query q;

	/* Reset state */
	pv->established = 0;
	atomic_set(&pv->seqno, 0);

	pr_devel("HVSI@%x: Handshaking started\n", pv->termno);

	/* Send version query */
	q.hdr.type = VS_QUERY_PACKET_HEADER;
	q.hdr.len = sizeof(struct hvsi_query);
	q.verb = cpu_to_be16(VSV_SEND_VERSION_NUMBER);
	hvsi_send_packet(pv, &q.hdr);
}

static int hvsi_send_close(struct hvsi_priv *pv)
{
	struct hvsi_control ctrl;

	pv->established = 0;

	ctrl.hdr.type = VS_CONTROL_PACKET_HEADER;
	ctrl.hdr.len = sizeof(struct hvsi_control);
	ctrl.verb = cpu_to_be16(VSV_CLOSE_PROTOCOL);
	return hvsi_send_packet(pv, &ctrl.hdr);
}

static void hvsi_cd_change(struct hvsi_priv *pv, int cd)
{
	if (cd)
		pv->mctrl |= TIOCM_CD;
	else {
		pv->mctrl &= ~TIOCM_CD;

		/* We copy the existing hvsi driver semantics
		 * here which are to trigger a hangup when
		 * we get a carrier loss.
		 * Closing our connection to the server will
		 * do just that.
		 */
		if (!pv->is_console && pv->opened) {
			pr_devel("HVSI@%x Carrier lost, hanging up !\n",
				 pv->termno);
			hvsi_send_close(pv);
		}
	}
}

static void hvsi_got_control(struct hvsi_priv *pv)
{
	struct hvsi_control *pkt = (struct hvsi_control *)pv->inbuf;

	switch (be16_to_cpu(pkt->verb)) {
	case VSV_CLOSE_PROTOCOL:
		/* We restart the handshaking */
		hvsi_start_handshake(pv);
		break;
	case VSV_MODEM_CTL_UPDATE:
		/* Transition of carrier detect */
		hvsi_cd_change(pv, be32_to_cpu(pkt->word) & HVSI_TSCD);
		break;
	}
}

static void hvsi_got_query(struct hvsi_priv *pv)
{
	struct hvsi_query *pkt = (struct hvsi_query *)pv->inbuf;
	struct hvsi_query_response r;

	/* We only handle version queries */
	if (be16_to_cpu(pkt->verb) != VSV_SEND_VERSION_NUMBER)
		return;

	pr_devel("HVSI@%x: Got version query, sending response...\n",
		 pv->termno);

	/* Send version response */
	r.hdr.type = VS_QUERY_RESPONSE_PACKET_HEADER;
	r.hdr.len = sizeof(struct hvsi_query_response);
	r.verb = cpu_to_be16(VSV_SEND_VERSION_NUMBER);
	r.u.version = HVSI_VERSION;
	r.query_seqno = pkt->hdr.seqno;
	hvsi_send_packet(pv, &r.hdr);

	/* Assume protocol is open now */
	pv->established = 1;
}

static void hvsi_got_response(struct hvsi_priv *pv)
{
	struct hvsi_query_response *r =
		(struct hvsi_query_response *)pv->inbuf;

	switch(r->verb) {
	case VSV_SEND_MODEM_CTL_STATUS:
		hvsi_cd_change(pv, be32_to_cpu(r->u.mctrl_word) & HVSI_TSCD);
		pv->mctrl_update = 1;
		break;
	}
}

static int hvsi_check_packet(struct hvsi_priv *pv)
{
	u8 len, type;

	/* Check header validity. If it's invalid, we ditch
	 * the whole buffer and hope we eventually resync
	 */
	if (pv->inbuf[0] < 0xfc) {
		pv->inbuf_len = pv->inbuf_pktlen = 0;
		return 0;
	}
	type = pv->inbuf[0];
	len = pv->inbuf[1];

	/* Packet incomplete ? */
	if (pv->inbuf_len < len)
		return 0;

	pr_devel("HVSI@%x: Got packet type %x len %d bytes:\n",
		 pv->termno, type, len);

	/* We have a packet, yay ! Handle it */
	switch(type) {
	case VS_DATA_PACKET_HEADER:
		pv->inbuf_pktlen = len - 4;
		pv->inbuf_cur = 4;
		return 1;
	case VS_CONTROL_PACKET_HEADER:
		hvsi_got_control(pv);
		break;
	case VS_QUERY_PACKET_HEADER:
		hvsi_got_query(pv);
		break;
	case VS_QUERY_RESPONSE_PACKET_HEADER:
		hvsi_got_response(pv);
		break;
	}

	/* Swallow packet and retry */
	pv->inbuf_len -= len;
	memmove(pv->inbuf, &pv->inbuf[len], pv->inbuf_len);
	return 1;
}

static int hvsi_get_packet(struct hvsi_priv *pv)
{
	/* If we have room in the buffer, ask HV for more */
	if (pv->inbuf_len < HVSI_INBUF_SIZE)
		pv->inbuf_len += pv->get_chars(pv->termno,
					     &pv->inbuf[pv->inbuf_len],
					     HVSI_INBUF_SIZE - pv->inbuf_len);
	/*
	 * If we have at least 4 bytes in the buffer, check for
	 * a full packet and retry
	 */
	if (pv->inbuf_len >= 4)
		return hvsi_check_packet(pv);
	return 0;
}

int hvsilib_get_chars(struct hvsi_priv *pv, char *buf, int count)
{
	unsigned int tries, read = 0;

	if (WARN_ON(!pv))
		return -ENXIO;

	/* If we aren't open, don't do anything in order to avoid races
	 * with connection establishment. The hvc core will call this
	 * before we have returned from notifier_add(), and we need to
	 * avoid multiple users playing with the receive buffer
	 */
	if (!pv->opened)
		return 0;

	/* We try twice, once with what data we have and once more
	 * after we try to fetch some more from the hypervisor
	 */
	for (tries = 1; count && tries < 2; tries++) {
		/* Consume existing data packet */
		if (pv->inbuf_pktlen) {
			unsigned int l = min(count, (int)pv->inbuf_pktlen);
			memcpy(&buf[read], &pv->inbuf[pv->inbuf_cur], l);
			pv->inbuf_cur += l;
			pv->inbuf_pktlen -= l;
			count -= l;
			read += l;
		}
		if (count == 0)
			break;

		/* Data packet fully consumed, move down remaning data */
		if (pv->inbuf_cur) {
			pv->inbuf_len -= pv->inbuf_cur;
			memmove(pv->inbuf, &pv->inbuf[pv->inbuf_cur],
				pv->inbuf_len);
			pv->inbuf_cur = 0;
		}

		/* Try to get another packet */
		if (hvsi_get_packet(pv))
			tries--;
	}
	if (!pv->established) {
		pr_devel("HVSI@%x: returning -EPIPE\n", pv->termno);
		return -EPIPE;
	}
	return read;
}

int hvsilib_put_chars(struct hvsi_priv *pv, const char *buf, int count)
{
	struct hvsi_data dp;
	int rc, adjcount = min(count, HVSI_MAX_OUTGOING_DATA);

	if (WARN_ON(!pv))
		return -ENODEV;

	dp.hdr.type = VS_DATA_PACKET_HEADER;
	dp.hdr.len = adjcount + sizeof(struct hvsi_header);
	memcpy(dp.data, buf, adjcount);
	rc = hvsi_send_packet(pv, &dp.hdr);
	if (rc <= 0)
		return rc;
	return adjcount;
}

static void maybe_msleep(unsigned long ms)
{
	/* During early boot, IRQs are disabled, use mdelay */
	if (irqs_disabled())
		mdelay(ms);
	else
		msleep(ms);
}

int hvsilib_read_mctrl(struct hvsi_priv *pv)
{
	struct hvsi_query q;
	int rc, timeout;

	pr_devel("HVSI@%x: Querying modem control status...\n",
		 pv->termno);

	pv->mctrl_update = 0;
	q.hdr.type = VS_QUERY_PACKET_HEADER;
	q.hdr.len = sizeof(struct hvsi_query);
	q.verb = cpu_to_be16(VSV_SEND_MODEM_CTL_STATUS);
	rc = hvsi_send_packet(pv, &q.hdr);
	if (rc <= 0) {
		pr_devel("HVSI@%x: Error %d...\n", pv->termno, rc);
		return rc;
	}

	/* Try for up to 200ms */
	for (timeout = 0; timeout < 20; timeout++) {
		if (!pv->established)
			return -ENXIO;
		if (pv->mctrl_update)
			return 0;
		if (!hvsi_get_packet(pv))
			maybe_msleep(10);
	}
	return -EIO;
}

int hvsilib_write_mctrl(struct hvsi_priv *pv, int dtr)
{
	struct hvsi_control ctrl;
	unsigned short mctrl;

	mctrl = pv->mctrl;
	if (dtr)
		mctrl |= TIOCM_DTR;
	else
		mctrl &= ~TIOCM_DTR;
	if (mctrl == pv->mctrl)
		return 0;
	pv->mctrl = mctrl;

	pr_devel("HVSI@%x: %s DTR...\n", pv->termno,
		 dtr ? "Setting" : "Clearing");

	ctrl.hdr.type = VS_CONTROL_PACKET_HEADER,
	ctrl.hdr.len = sizeof(struct hvsi_control);
	ctrl.verb = cpu_to_be16(VSV_SET_MODEM_CTL);
	ctrl.mask = cpu_to_be32(HVSI_TSDTR);
	ctrl.word = cpu_to_be32(dtr ? HVSI_TSDTR : 0);
	return hvsi_send_packet(pv, &ctrl.hdr);
}

void hvsilib_establish(struct hvsi_priv *pv)
{
	int timeout;

	pr_devel("HVSI@%x: Establishing...\n", pv->termno);

	/* Try for up to 200ms, there can be a packet to
	 * start the process waiting for us...
	 */
	for (timeout = 0; timeout < 20; timeout++) {
		if (pv->established)
			goto established;
		if (!hvsi_get_packet(pv))
			maybe_msleep(10);
	}

	/* Failed, send a close connection packet just
	 * in case
	 */
	pr_devel("HVSI@%x:   ... sending close\n", pv->termno);

	hvsi_send_close(pv);

	/* Then restart handshake */

	pr_devel("HVSI@%x:   ... restarting handshake\n", pv->termno);

	hvsi_start_handshake(pv);

	pr_devel("HVSI@%x:   ... waiting handshake\n", pv->termno);

	/* Try for up to 400ms */
	for (timeout = 0; timeout < 40; timeout++) {
		if (pv->established)
			goto established;
		if (!hvsi_get_packet(pv))
			maybe_msleep(10);
	}

	if (!pv->established) {
		pr_devel("HVSI@%x: Timeout handshaking, giving up !\n",
			 pv->termno);
		return;
	}
 established:
	/* Query modem control lines */

	pr_devel("HVSI@%x:   ... established, reading mctrl\n", pv->termno);

	hvsilib_read_mctrl(pv);

	/* Set our own DTR */

	pr_devel("HVSI@%x:   ... setting mctrl\n", pv->termno);

	hvsilib_write_mctrl(pv, 1);

	/* Set the opened flag so reads are allowed */
	wmb();
	pv->opened = 1;
}

int hvsilib_open(struct hvsi_priv *pv, struct hvc_struct *hp)
{
	pr_devel("HVSI@%x: open !\n", pv->termno);

	/* Keep track of the tty data structure */
	pv->tty = tty_port_tty_get(&hp->port);

	hvsilib_establish(pv);

	return 0;
}

void hvsilib_close(struct hvsi_priv *pv, struct hvc_struct *hp)
{
	unsigned long flags;

	pr_devel("HVSI@%x: close !\n", pv->termno);

	if (!pv->is_console) {
		pr_devel("HVSI@%x: Not a console, tearing down\n",
			 pv->termno);

		/* Clear opened, synchronize with khvcd */
		spin_lock_irqsave(&hp->lock, flags);
		pv->opened = 0;
		spin_unlock_irqrestore(&hp->lock, flags);

		/* Clear our own DTR */
		if (!pv->tty || (pv->tty->termios.c_cflag & HUPCL))
			hvsilib_write_mctrl(pv, 0);

		/* Tear down the connection */
		hvsi_send_close(pv);
	}

	tty_kref_put(pv->tty);
	pv->tty = NULL;
}

void hvsilib_init(struct hvsi_priv *pv,
		  int (*get_chars)(uint32_t termno, char *buf, int count),
		  int (*put_chars)(uint32_t termno, const char *buf,
				   int count),
		  int termno, int is_console)
{
	memset(pv, 0, sizeof(*pv));
	pv->get_chars = get_chars;
	pv->put_chars = put_chars;
	pv->termno = termno;
	pv->is_console = is_console;
}