staging/speakup_soft: Fix alternate speech with other synths

[Samuel Thibault <samuel.thibault@ens-lyon.org>]

When switching from speakup_soft to another synth, speakup_soft would
keep calling synth_buffer_getc() from softsynthx_read.

Let's thus make synth.c export the knowledge of the current synth, so
that speakup_soft can determine whether it should be running.

speakup_soft also needs to set itself alive, otherwise the switch would
let it remain silent.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
---
 drivers/staging/speakup/speakup_soft.c |   16 +++++++++++-----
 drivers/staging/speakup/spk_priv.h     |    1 +
 drivers/staging/speakup/synth.c        |    6 ++++++
 3 files changed, 18 insertions(+), 5 deletions(-)

--- a/drivers/staging/speakup/speakup_soft.c
+++ b/drivers/staging/speakup/speakup_soft.c
@@ -208,12 +208,15 @@ static ssize_t softsynthx_read(struct fi
 		return -EINVAL;
 
 	spin_lock_irqsave(&speakup_info.spinlock, flags);
+	synth_soft.alive = 1;
 	while (1) {
 		prepare_to_wait(&speakup_event, &wait, TASK_INTERRUPTIBLE);
-		if (!unicode)
-			synth_buffer_skip_nonlatin1();
-		if (!synth_buffer_empty() || speakup_info.flushing)
-			break;
+		if (synth_current() == &synth_soft) {
+			if (!unicode)
+				synth_buffer_skip_nonlatin1();
+			if (!synth_buffer_empty() || speakup_info.flushing)
+				break;
+		}
 		spin_unlock_irqrestore(&speakup_info.spinlock, flags);
 		if (fp->f_flags & O_NONBLOCK) {
 			finish_wait(&speakup_event, &wait);
@@ -233,6 +236,8 @@ static ssize_t softsynthx_read(struct fi
 
 	/* Keep 3 bytes available for a 16bit UTF-8-encoded character */
 	while (chars_sent <= count - bytes_per_ch) {
+		if (synth_current() != &synth_soft)
+			break;
 		if (speakup_info.flushing) {
 			speakup_info.flushing = 0;
 			ch = '\x18';
@@ -329,7 +334,8 @@ static __poll_t softsynth_poll(struct fi
 	poll_wait(fp, &speakup_event, wait);
 
 	spin_lock_irqsave(&speakup_info.spinlock, flags);
-	if (!synth_buffer_empty() || speakup_info.flushing)
+	if (synth_current() == &synth_soft &&
+	    (!synth_buffer_empty() || speakup_info.flushing))
 		ret = EPOLLIN | EPOLLRDNORM;
 	spin_unlock_irqrestore(&speakup_info.spinlock, flags);
 	return ret;
--- a/drivers/staging/speakup/spk_priv.h
+++ b/drivers/staging/speakup/spk_priv.h
@@ -72,6 +72,7 @@ int synth_request_region(unsigned long s
 int synth_release_region(unsigned long start, unsigned long n);
 int synth_add(struct spk_synth *in_synth);
 void synth_remove(struct spk_synth *in_synth);
+struct spk_synth *synth_current(void);
 
 extern struct speakup_info_t speakup_info;
 
--- a/drivers/staging/speakup/synth.c
+++ b/drivers/staging/speakup/synth.c
@@ -495,4 +495,10 @@ void synth_remove(struct spk_synth *in_s
 }
 EXPORT_SYMBOL_GPL(synth_remove);
 
+struct spk_synth *synth_current(void)
+{
+	return synth;
+}
+EXPORT_SYMBOL_GPL(synth_current);
+
 short spk_punc_masks[] = { 0, SOME, MOST, PUNC, PUNC | B_SYM };