powerpc/pseries: Fix hvterm_raw_get_chars to accept < 16 chars, fixing xmon

commit 4d2bb3f50036 (powerpc/pseries: Re-implement HVSI as part of
hvc_vio) changed udbg_getc to be based on hvterm_raw_get_chars.
Unfortunately hvterm_raw_get_chars returns -EAGAIN if you ask
for anything less than 16 characters. As a result xmon no longer
accepts input and prints a stream of junk to the screen.

The recent change highlights a problem that xmon on pseries VIO
has had all along, that it can drop input characters. The issue
is the hypervisor call does not take a count argument and can
return up to 16 characters.

This patch adds a per vterm buffer that we copy input data into
and give it out as requested.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 37 insertions, 21 deletions

diff --git a/drivers/tty/hvc/hvc_vio.c b/drivers/tty/hvc/hvc_vio.c
index 710c06ca70f..ae659a4596b 100644
--- a/drivers/tty/hvc/hvc_vio.c
+++ b/drivers/tty/hvc/hvc_vio.c
@@ -71,41 +71,53 @@ struct hvterm_priv {
         u32                     termno; /* HV term number */
         hv_protocol_t           proto;  /* Raw data or HVSI packets */
         struct hvsi_priv        hvsi;   /* HVSI specific data */
+        spinlock_t              buf_lock;
+        char                    buf[SIZE_VIO_GET_CHARS];
+        int                     left;
+        int                     offset;
 };
 static struct hvterm_priv *hvterm_privs[MAX_NR_HVC_CONSOLES];
-
 /* For early boot console */
 static struct hvterm_priv hvterm_priv0;
 
 static int hvterm_raw_get_chars(uint32_t vtermno, char *buf, int count)
 {
         struct hvterm_priv *pv = hvterm_privs[vtermno];
-        unsigned long got, i;
+        unsigned long i;
+        unsigned long flags;
+        int got;
 
         if (WARN_ON(!pv))
                 return 0;
 
-        /*
-         * Vio firmware will read up to SIZE_VIO_GET_CHARS at its own discretion
-         * so we play safe and avoid the situation where got > count which could
-         * overload the flip buffer.
-         */
-        if (count < SIZE_VIO_GET_CHARS)
-                return -EAGAIN;
-
-        got = hvc_get_chars(pv->termno, buf, count);
-
-        /*
-         * Work around a HV bug where it gives us a null
-         * after every \r.  -- paulus
-         */
-        for (i = 1; i < got; ++i) {
-                if (buf[i] == 0 && buf[i-1] == '\r') {
-                        --got;
-                        if (i < got)
-                                memmove(&buf[i], &buf[i+1], got - i);
+        spin_lock_irqsave(&pv->buf_lock, flags);
+
+        if (pv->left == 0) {
+                pv->offset = 0;
+                pv->left = hvc_get_chars(pv->termno, pv->buf, count);
+
+                /*
+                 * Work around a HV bug where it gives us a null
+                 * after every \r.  -- paulus
+                 */
+                for (i = 1; i < pv->left; ++i) {
+                        if (pv->buf[i] == 0 && pv->buf[i-1] == '\r') {
+                                --pv->left;
+                                if (i < pv->left) {
+                                        memmove(&pv->buf[i], &pv->buf[i+1],
+                                                pv->left - i);
+                                }
+                        }
                 }
         }
+
+        got = min(count, pv->left);
+        memcpy(buf, &pv->buf[pv->offset], got);
+        pv->offset += got;
+        pv->left -= got;
+
+        spin_unlock_irqrestore(&pv->buf_lock, flags);
+
         return got;
 }
 
@@ -266,6 +278,7 @@ static int __devinit hvc_vio_probe(struct vio_dev *vdev,
                         return -ENOMEM;
                 pv->termno = vdev->unit_address;
                 pv->proto = proto;
+                spin_lock_init(&pv->buf_lock);
                 hvterm_privs[termno] = pv;
                 hvsilib_init(&pv->hvsi, hvc_get_chars, hvc_put_chars,
                              pv->termno, 0);
@@ -406,6 +419,7 @@ void __init hvc_vio_init_early(void)
         if (termno == NULL)
                 goto out;
         hvterm_priv0.termno = *termno;
+        spin_lock_init(&hvterm_priv0.buf_lock);
         hvterm_privs[0] = &hvterm_priv0;
 
         /* Check the protocol */
@@ -447,6 +461,7 @@ void __init udbg_init_debug_lpar(void)
         hvterm_privs[0] = &hvterm_priv0;
         hvterm_priv0.termno = 0;
         hvterm_priv0.proto = HV_PROTOCOL_RAW;
+        spin_lock_init(&hvterm_priv0.buf_lock)
         udbg_putc = udbg_hvc_putc;
         udbg_getc = udbg_hvc_getc;
         udbg_getc_poll = udbg_hvc_getc_poll;
@@ -459,6 +474,7 @@ void __init udbg_init_debug_lpar_hvsi(void)
         hvterm_privs[0] = &hvterm_priv0;
         hvterm_priv0.termno = CONFIG_PPC_EARLY_DEBUG_HVSI_VTERMNO;
         hvterm_priv0.proto = HV_PROTOCOL_HVSI;
+        spin_lock_init(&hvterm_priv0.buf_lock)
         udbg_putc = udbg_hvc_putc;
         udbg_getc = udbg_hvc_getc;
         udbg_getc_poll = udbg_hvc_getc_poll;