[PATCH 7/7] hvc: add an M3000 firmware console backend

[Magnus Lindholm <linmag7@gmail.com>]

Provide hvc0 through the IKKAKU Open Firmware pseudo-console, validating
model and console properties before matching. Serialize firmware calls,
keep the bounce buffer in locked mappings and poll input each open tick.

Keep output buffers const and bound no-progress retries because HVC
retries EAGAIN indefinitely. A stalled firmware call remains unbounded.
Use the existing SPARC p1275 interface and HVC output contract.

Signed-off-by: Magnus Lindholm <linmag7@gmail.com>
---
 MAINTAINERS                 |   6 ++
 drivers/tty/hvc/Kconfig     |  10 +++
 drivers/tty/hvc/Makefile    |   2 +
 drivers/tty/hvc/hvc_m3000.c | 167 ++++++++++++++++++++++++++++++++++++
 4 files changed, 185 insertions(+)
 create mode 100644 drivers/tty/hvc/hvc_m3000.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 3a19da74d00c..5bc9b1cabd0a 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -10728,6 +10728,12 @@ L:	platform-driver-x86@vger.kernel.org
 S:	Maintained
 F:	drivers/platform/x86/fujitsu-laptop.c
 
+FUJITSU M3000 FIRMWARE CONSOLE
+M:	Magnus Lindholm <linmag7@gmail.com>
+L:	linux-serial@vger.kernel.org
+S:	Maintained
+F:	drivers/tty/hvc/hvc_m3000.c
+
 FUJITSU TABLET EXTRAS
 M:	Robert Gerlach <khnz@gmx.de>
 L:	platform-driver-x86@vger.kernel.org
diff --git a/drivers/tty/hvc/Kconfig b/drivers/tty/hvc/Kconfig
index 5866195de26a..0feb7ec98f4f 100644
--- a/drivers/tty/hvc/Kconfig
+++ b/drivers/tty/hvc/Kconfig
@@ -134,3 +134,13 @@ config HVCS
 	  will depend on arch specific APIs exported from hvcserver.ko
 	  which will also be compiled when this driver is built as a
 	  module.
+
+config HVC_M3000
+	bool "M3000 firmware pseudo-console"
+	depends on SPARC64_VII
+	select HVC_DRIVER
+	help
+	  Provide hvc0 using Open Firmware stdin/stdout on IKKAKU only.
+	  Input is polled; no native UART registers are accessed.
+	  Firmware calls are serialized and use a locked-image bounce buffer.
+	  Say Y to use the M3000 firmware pseudo-console as hvc0.
diff --git a/drivers/tty/hvc/Makefile b/drivers/tty/hvc/Makefile
index 98880e357941..5b0277deb7c9 100644
--- a/drivers/tty/hvc/Makefile
+++ b/drivers/tty/hvc/Makefile
@@ -11,3 +11,5 @@ obj-$(CONFIG_HVC_IUCV)		+= hvc_iucv.o
 obj-$(CONFIG_HVC_UDBG)		+= hvc_udbg.o
 obj-$(CONFIG_HVC_RISCV_SBI)	+= hvc_riscv_sbi.o
 obj-$(CONFIG_HVCS)		+= hvcs.o
+
+obj-$(CONFIG_HVC_M3000) += hvc_m3000.o
diff --git a/drivers/tty/hvc/hvc_m3000.c b/drivers/tty/hvc/hvc_m3000.c
new file mode 100644
index 000000000000..0ef4c888a6a2
--- /dev/null
+++ b/drivers/tty/hvc/hvc_m3000.c
@@ -0,0 +1,167 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Experimental M3000 Open Firmware pseudo-console backend. */
+#include <linux/console.h>
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/irqflags.h>
+#include <linux/string.h>
+#include <linux/spinlock.h>
+#include <linux/timer.h>
+#include <asm/oplib.h>
+#include <asm/spitfire.h>
+#include "hvc_console.h"
+
+#define M3000_WRITE_ATTEMPTS 8
+
+static int m3000_stdin;
+static bool m3000_ready;
+/* Keep firmware buffers within the locked kernel image mappings. */
+static u8 m3000_buffer[256];
+static DEFINE_RAW_SPINLOCK(m3000_buffer_lock);
+static struct timer_list m3000_poll_timer;
+static bool m3000_poll_active;
+
+/*
+ * HVC's idle backoff can exceed the firmware input FIFO's capacity.
+ * Wake its worker each tick while open; keep PROM calls out of the timer.
+ */
+static void m3000_poll_tick(struct timer_list *timer)
+{
+	if (!READ_ONCE(m3000_poll_active))
+		return;
+	hvc_kick();
+	mod_timer(&m3000_poll_timer, jiffies + 1);
+}
+
+static int m3000_open(struct hvc_struct *hp, int data)
+{
+	WRITE_ONCE(m3000_poll_active, true);
+	mod_timer(&m3000_poll_timer, jiffies + 1);
+	return 0;
+}
+
+static void m3000_close(struct hvc_struct *hp, int data)
+{
+	WRITE_ONCE(m3000_poll_active, false);
+	timer_delete_sync(&m3000_poll_timer);
+}
+
+static ssize_t m3000_io(u8 *in, const u8 *out, size_t count)
+{
+	unsigned long args[7], flags;
+	bool input = in != NULL;
+	int ret;
+
+	if (!count)
+		return 0;
+	count = min_t(size_t, count, input ? 1 : sizeof(m3000_buffer));
+	/* Serialize the bounce buffer; p1275 separately serializes firmware. */
+	raw_spin_lock_irqsave(&m3000_buffer_lock, flags);
+	if (!input)
+		memcpy(m3000_buffer, out, count);
+	args[0] = (unsigned long)(input ? "read" : "write");
+	args[1] = 3;
+	args[2] = 1;
+	args[3] = (unsigned int)(input ? m3000_stdin : prom_stdout);
+	args[4] = (unsigned long)m3000_buffer;
+	args[5] = count;
+	args[6] = (unsigned long)-1;
+	p1275_cmd_direct(args);
+	ret = (int)args[6];
+	if (ret > 0 && ret <= count && input)
+		memcpy(in, m3000_buffer, ret);
+	raw_spin_unlock_irqrestore(&m3000_buffer_lock, flags);
+	if (ret == -2 || ret == 0)
+		return input ? 0 : -EAGAIN;
+	if (ret < 0 || ret > count)
+		return -EIO;
+	return ret;
+}
+
+static ssize_t m3000_get(u32 termno, u8 *buf, size_t count)
+{
+	return m3000_io(buf, NULL, count);
+}
+
+static ssize_t m3000_put(u32 termno, const u8 *buf, size_t count)
+{
+	ssize_t ret;
+	int attempt;
+
+	/*
+	 * HVC retries -EAGAIN forever, so drop this chunk without logging when
+	 * the no-progress budget expires. This cannot bound a stalled firmware
+	 * call or lock acquisition.
+	 */
+	for (attempt = 0; attempt < M3000_WRITE_ATTEMPTS; attempt++) {
+		ret = m3000_io(NULL, buf, count);
+		if (ret != -EAGAIN)
+			return ret;
+		cpu_relax();
+	}
+	return -EIO;
+}
+
+static const struct hv_ops m3000_ops = {
+	.get_chars = m3000_get,
+	.put_chars = m3000_put,
+	.notifier_add = m3000_open,
+	.notifier_del = m3000_close,
+	.notifier_hangup = m3000_close,
+};
+
+static bool __init m3000_property_matches(phandle node, const char *prop,
+					 const char *expected)
+{
+	char value[64];
+	int len;
+
+	len = prom_getproperty(node, prop, value, sizeof(value) - 1);
+	if (len <= 0)
+		return false;
+	value[len] = '\0';
+	return !strcmp(value, expected);
+}
+
+static int __init m3000_console_init(void)
+{
+	phandle node;
+	int ret;
+
+	if (tlb_type != sparc64_vii)
+		return -ENODEV;
+	if (!m3000_property_matches(prom_finddevice("/"), "model", "IKKAKU"))
+		return -ENODEV;
+	m3000_stdin = prom_getint(prom_chosen_node, "stdin");
+	if (!m3000_stdin || m3000_stdin == -1 || !prom_stdout || prom_stdout == -1)
+		return -ENODEV;
+	node = prom_inst2pkg(prom_stdout);
+	if (!m3000_property_matches(node, "name", "pseudo-console"))
+		return -ENODEV;
+	node = prom_inst2pkg(m3000_stdin);
+	if (!m3000_property_matches(node, "name", "pseudo-console"))
+		return -ENODEV;
+	ret = hvc_instantiate(0, 0, &m3000_ops);
+	if (ret < 0)
+		return ret;
+	m3000_ready = true;
+	return 0;
+}
+console_initcall(m3000_console_init);
+
+static int __init m3000_tty_init(void)
+{
+	struct hvc_struct *hp;
+
+	if (!m3000_ready)
+		return -ENODEV;
+	timer_setup(&m3000_poll_timer, m3000_poll_tick, 0);
+	hp = hvc_alloc(0, 0, &m3000_ops, sizeof(m3000_buffer));
+	if (IS_ERR(hp))
+		return PTR_ERR(hp);
+	hp->ws.ws_row = 24;
+	hp->ws.ws_col = 80;
+	pr_info("M3000: firmware-backed hvc0 tty ready (serialized, polled input)\n");
+	return 0;
+}
+device_initcall(m3000_tty_init);
-- 
2.43.0