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>

diff --git a/drivers/tty/hvc/hvc_vio.c b/drivers/tty/hvc/hvc_vio.c
index 710c06ca70f499bcec49ebca18230b39fe4b1d9b..ae659a4596b066391bcb6215bedea718a453aa9c 100644 (file)
--- 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;