staging: speakup_soft: Fix alternate speech with other synths

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>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/speakup/speakup_soft.c

@@ -210,12 +210,15 @@ static ssize_t softsynthx_read(struct file *fp, char __user *buf, size_t count,
 		return -EINVAL;
 
 	spin_lock_irqsave(&speakup_info.spinlock, flags);
+	synth_soft.alive = 1;
 	while (1) {
 		prepare_to_wait(&speakup_event, &wait, TASK_INTERRUPTIBLE);
+		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);
@@ -235,6 +238,8 @@ static ssize_t softsynthx_read(struct file *fp, char __user *buf, size_t count,
 
 	/* 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';
@@ -331,7 +336,8 @@ static __poll_t softsynth_poll(struct file *fp, struct poll_table_struct *wait)
 	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;

drivers/staging/speakup/spk_priv.h

@@ -74,6 +74,7 @@ int synth_request_region(unsigned long start, unsigned long n);
 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;
 

drivers/staging/speakup/synth.c

@@ -481,4 +481,10 @@ void synth_remove(struct spk_synth *in_synth)
 }
 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 };