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Subject[PATCH 08/15] powerpc/powernv: implement opal_put_chars_atomic
Date
The RAW console does not need writes to be atomic, so relax
opal_put_chars to be able to do partial writes, and implement an
_atomic variant which does not take a spinlock. This API is used
in xmon, so the less locking that is used, the better chance there
is that a crash can be debugged.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
arch/powerpc/include/asm/opal.h | 1 +
arch/powerpc/platforms/powernv/opal.c | 37 +++++++++++++++++++--------
drivers/tty/hvc/hvc_opal.c | 18 +++++++++----
3 files changed, 41 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/include/asm/opal.h b/arch/powerpc/include/asm/opal.h
index bbff49fab0e5..5d7072411561 100644
--- a/arch/powerpc/include/asm/opal.h
+++ b/arch/powerpc/include/asm/opal.h
@@ -303,6 +303,7 @@ extern void opal_configure_cores(void);

extern int opal_get_chars(uint32_t vtermno, char *buf, int count);
extern int opal_put_chars(uint32_t vtermno, const char *buf, int total_len);
+extern int opal_put_chars_atomic(uint32_t vtermno, const char *buf, int total_len);
extern int opal_flush_console(uint32_t vtermno);

extern void hvc_opal_init_early(void);
diff --git a/arch/powerpc/platforms/powernv/opal.c b/arch/powerpc/platforms/powernv/opal.c
index 55d4b1983110..bcdb90ada938 100644
--- a/arch/powerpc/platforms/powernv/opal.c
+++ b/arch/powerpc/platforms/powernv/opal.c
@@ -344,9 +344,9 @@ int opal_get_chars(uint32_t vtermno, char *buf, int count)
return 0;
}

-int opal_put_chars(uint32_t vtermno, const char *data, int total_len)
+static int __opal_put_chars(uint32_t vtermno, const char *data, int total_len, bool atomic)
{
- unsigned long flags;
+ unsigned long flags = 0 /* shut up gcc */;
int written;
__be64 olen;
s64 rc;
@@ -354,11 +354,8 @@ int opal_put_chars(uint32_t vtermno, const char *data, int total_len)
if (!opal.entry)
return -ENODEV;

- /* We want put_chars to be atomic to avoid mangling of hvsi
- * packets. To do that, we first test for room and return
- * -EAGAIN if there isn't enough.
- */
- spin_lock_irqsave(&opal_write_lock, flags);
+ if (atomic)
+ spin_lock_irqsave(&opal_write_lock, flags);
rc = opal_console_write_buffer_space(vtermno, &olen);
if (rc || be64_to_cpu(olen) < total_len) {
/* Closed -> drop characters */
@@ -391,14 +388,18 @@ int opal_put_chars(uint32_t vtermno, const char *data, int total_len)

written = be64_to_cpu(olen);
if (written < total_len) {
- /* Should not happen */
- pr_warn("atomic console write returned partial len=%d written=%d\n", total_len, written);
+ if (atomic) {
+ /* Should not happen */
+ pr_warn("atomic console write returned partial "
+ "len=%d written=%d\n", total_len, written);
+ }
if (!written)
written = -EAGAIN;
}

out:
- spin_unlock_irqrestore(&opal_write_lock, flags);
+ if (atomic)
+ spin_unlock_irqrestore(&opal_write_lock, flags);

/* In the -EAGAIN case, callers loop, so we have to flush the console
* here in case they have interrupts off (and we don't want to wait
@@ -412,6 +413,22 @@ int opal_put_chars(uint32_t vtermno, const char *data, int total_len)
return written;
}

+int opal_put_chars(uint32_t vtermno, const char *data, int total_len)
+{
+ return __opal_put_chars(vtermno, data, total_len, false);
+}
+
+/*
+ * opal_put_chars_atomic will not perform partial-writes. Data will be
+ * atomically written to the terminal or not at all. This is not strictly
+ * true at the moment because console space can race with OPAL's console
+ * writes.
+ */
+int opal_put_chars_atomic(uint32_t vtermno, const char *data, int total_len)
+{
+ return __opal_put_chars(vtermno, data, total_len, true);
+}
+
int opal_flush_console(uint32_t vtermno)
{
s64 rc;
diff --git a/drivers/tty/hvc/hvc_opal.c b/drivers/tty/hvc/hvc_opal.c
index af122ad7f06d..0a72f98ee082 100644
--- a/drivers/tty/hvc/hvc_opal.c
+++ b/drivers/tty/hvc/hvc_opal.c
@@ -183,9 +183,15 @@ static int hvc_opal_probe(struct platform_device *dev)
return -ENOMEM;
pv->proto = proto;
hvc_opal_privs[termno] = pv;
- if (proto == HV_PROTOCOL_HVSI)
- hvsilib_init(&pv->hvsi, opal_get_chars, opal_put_chars,
+ if (proto == HV_PROTOCOL_HVSI) {
+ /*
+ * We want put_chars to be atomic to avoid mangling of
+ * hvsi packets.
+ */
+ hvsilib_init(&pv->hvsi,
+ opal_get_chars, opal_put_chars_atomic,
termno, 0);
+ }

/* Instanciate now to establish a mapping index==vtermno */
hvc_instantiate(termno, termno, ops);
@@ -376,8 +382,9 @@ void __init hvc_opal_init_early(void)
else if (of_device_is_compatible(stdout_node,"ibm,opal-console-hvsi")) {
hvc_opal_boot_priv.proto = HV_PROTOCOL_HVSI;
ops = &hvc_opal_hvsi_ops;
- hvsilib_init(&hvc_opal_boot_priv.hvsi, opal_get_chars,
- opal_put_chars, index, 1);
+ hvsilib_init(&hvc_opal_boot_priv.hvsi,
+ opal_get_chars, opal_put_chars_atomic,
+ index, 1);
/* HVSI, perform the handshake now */
hvsilib_establish(&hvc_opal_boot_priv.hvsi);
pr_devel("hvc_opal: Found HVSI console\n");
@@ -409,7 +416,8 @@ void __init udbg_init_debug_opal_hvsi(void)
hvc_opal_privs[index] = &hvc_opal_boot_priv;
hvc_opal_boot_termno = index;
udbg_init_opal_common();
- hvsilib_init(&hvc_opal_boot_priv.hvsi, opal_get_chars, opal_put_chars,
+ hvsilib_init(&hvc_opal_boot_priv.hvsi,
+ opal_get_chars, opal_put_chars_atomic,
index, 1);
hvsilib_establish(&hvc_opal_boot_priv.hvsi);
}
--
2.17.0
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