OMAP: mailbox: add notification support for multiple readers

In the current mailbox driver, the mailbox internal pointer for
callback can be directly manipulated by the Users, so a second
User can easily corrupt the first user's callback pointer.
The initial effort to correct this issue can be referred here:
https://patchwork.kernel.org/patch/107520/

Along with fixing the above stated issue, this patch  adds the
flexibility option to register notifications from
multiple readers to the events received on a mailbox instance.
The discussion regarding this can be referred here.
http://www.mail-archive.com/linux-omap@vger.kernel.org/msg30671.html

Signed-off-by: Hari Kanigeri <h-kanigeri2@ti.com>
Signed-off-by: Fernando Guzman Lugo <x0095840@ti.com>
Acked-by: Hiroshi Doyu <hiroshi.doyu@nokia.com>

2 files changed, 61 insertions, 49 deletions

diff --git a/arch/arm/plat-omap/include/plat/mailbox.h b/arch/arm/plat-omap/include/plat/mailbox.h
index 13f2ef3ea0ff..cc3921e9059c 100644
--- a/arch/arm/plat-omap/include/plat/mailbox.h
+++ b/arch/arm/plat-omap/include/plat/mailbox.h
@@ -46,7 +46,6 @@ struct omap_mbox_queue {
         struct kfifo            fifo;
         struct work_struct      work;
         struct tasklet_struct   tasklet;
-        int     (*callback)(void *);
         struct omap_mbox        *mbox;
         bool full;
 };
@@ -58,13 +57,15 @@ struct omap_mbox {
         struct omap_mbox_ops    *ops;
         struct device           *dev;
         void                    *priv;
+        int                     use_count;
+        struct blocking_notifier_head   notifier;
 };
 
 int omap_mbox_msg_send(struct omap_mbox *, mbox_msg_t msg);
 void omap_mbox_init_seq(struct omap_mbox *);
 
-struct omap_mbox *omap_mbox_get(const char *);
-void omap_mbox_put(struct omap_mbox *);
+struct omap_mbox *omap_mbox_get(const char *, struct notifier_block *nb);
+void omap_mbox_put(struct omap_mbox *mbox, struct notifier_block *nb);
 
 int omap_mbox_register(struct device *parent, struct omap_mbox **);
 int omap_mbox_unregister(void);
diff --git a/arch/arm/plat-omap/mailbox.c b/arch/arm/plat-omap/mailbox.c
index cc58b44325f2..459b319a9fad 100644
--- a/arch/arm/plat-omap/mailbox.c
+++ b/arch/arm/plat-omap/mailbox.c
@@ -28,6 +28,7 @@
 #include <linux/slab.h>
 #include <linux/kfifo.h>
 #include <linux/err.h>
+#include <linux/notifier.h>
 
 #include <plat/mailbox.h>
 
@@ -150,8 +151,8 @@ static void mbox_rx_work(struct work_struct *work)
                 len = kfifo_out(&mq->fifo, (unsigned char *)&msg, sizeof(msg));
                 WARN_ON(len != sizeof(msg));
 
-                if (mq->callback)
-                        mq->callback((void *)msg);
+                blocking_notifier_call_chain(&mq->mbox->notifier, len,
+                                                                (void *)msg);
                 spin_lock_irq(&mq->lock);
                 if (mq->full) {
                         mq->full = false;
@@ -249,41 +250,40 @@ static int omap_mbox_startup(struct omap_mbox *mbox)
         int ret = 0;
         struct omap_mbox_queue *mq;
 
-        if (mbox->ops->startup) {
-                mutex_lock(&mbox_configured_lock);
-                if (!mbox_configured)
+        mutex_lock(&mbox_configured_lock);
+        if (!mbox_configured++) {
+                if (likely(mbox->ops->startup)) {
                         ret = mbox->ops->startup(mbox);
-
-                if (ret) {
-                        mutex_unlock(&mbox_configured_lock);
-                        return ret;
-                }
-                mbox_configured++;
-                mutex_unlock(&mbox_configured_lock);
+                        if (unlikely(ret))
+                                goto fail_startup;
+                } else
+                        goto fail_startup;
         }
 
-        ret = request_irq(mbox->irq, mbox_interrupt, IRQF_SHARED,
-                                mbox->name, mbox);
-        if (ret) {
-                printk(KERN_ERR
-                        "failed to register mailbox interrupt:%d\n", ret);
-                goto fail_request_irq;
-        }
-
-        mq = mbox_queue_alloc(mbox, NULL, mbox_tx_tasklet);
-        if (!mq) {
-                ret = -ENOMEM;
-                goto fail_alloc_txq;
-        }
-        mbox->txq = mq;
+        if (!mbox->use_count++) {
+                ret = request_irq(mbox->irq, mbox_interrupt, IRQF_SHARED,
+                                                        mbox->name, mbox);
+                if (unlikely(ret)) {
+                        pr_err("failed to register mailbox interrupt:%d\n",
+                                                                        ret);
+                        goto fail_request_irq;
+                }
+                mq = mbox_queue_alloc(mbox, NULL, mbox_tx_tasklet);
+                if (!mq) {
+                        ret = -ENOMEM;
+                        goto fail_alloc_txq;
+                }
+                mbox->txq = mq;
 
-        mq = mbox_queue_alloc(mbox, mbox_rx_work, NULL);
-        if (!mq) {
-                ret = -ENOMEM;
-                goto fail_alloc_rxq;
+                mq = mbox_queue_alloc(mbox, mbox_rx_work, NULL);
+                if (!mq) {
+                        ret = -ENOMEM;
+                        goto fail_alloc_rxq;
+                }
+                mbox->rxq = mq;
+                mq->mbox = mbox;
         }
-        mbox->rxq = mq;
-
+        mutex_unlock(&mbox_configured_lock);
         return 0;
 
 fail_alloc_rxq:
@@ -293,29 +293,34 @@ fail_alloc_txq:
 fail_request_irq:
         if (mbox->ops->shutdown)
                 mbox->ops->shutdown(mbox);
-
+        mbox->use_count--;
+fail_startup:
+        mbox_configured--;
+        mutex_unlock(&mbox_configured_lock);
         return ret;
 }
 
 static void omap_mbox_fini(struct omap_mbox *mbox)
 {
-        free_irq(mbox->irq, mbox);
-        tasklet_kill(&mbox->txq->tasklet);
-        flush_work(&mbox->rxq->work);
-        mbox_queue_free(mbox->txq);
-        mbox_queue_free(mbox->rxq);
+        mutex_lock(&mbox_configured_lock);
+
+        if (!--mbox->use_count) {
+                free_irq(mbox->irq, mbox);
+                tasklet_kill(&mbox->txq->tasklet);
+                flush_work(&mbox->rxq->work);
+                mbox_queue_free(mbox->txq);
+                mbox_queue_free(mbox->rxq);
+        }
 
-        if (mbox->ops->shutdown) {
-                mutex_lock(&mbox_configured_lock);
-                if (mbox_configured > 0)
-                        mbox_configured--;
-                if (!mbox_configured)
+        if (likely(mbox->ops->shutdown)) {
+                if (!--mbox_configured)
                         mbox->ops->shutdown(mbox);
-                mutex_unlock(&mbox_configured_lock);
         }
+
+        mutex_unlock(&mbox_configured_lock);
 }
 
-struct omap_mbox *omap_mbox_get(const char *name)
+struct omap_mbox *omap_mbox_get(const char *name, struct notifier_block *nb)
 {
         struct omap_mbox *mbox;
         int ret;
@@ -334,12 +339,16 @@ struct omap_mbox *omap_mbox_get(const char *name)
         if (ret)
                 return ERR_PTR(-ENODEV);
 
+        if (nb)
+                blocking_notifier_chain_register(&mbox->notifier, nb);
+
         return mbox;
 }
 EXPORT_SYMBOL(omap_mbox_get);
 
-void omap_mbox_put(struct omap_mbox *mbox)
+void omap_mbox_put(struct omap_mbox *mbox, struct notifier_block *nb)
 {
+        blocking_notifier_chain_unregister(&mbox->notifier, nb);
         omap_mbox_fini(mbox);
 }
 EXPORT_SYMBOL(omap_mbox_put);
@@ -363,6 +372,8 @@ int omap_mbox_register(struct device *parent, struct omap_mbox **list)
                         ret = PTR_ERR(mbox->dev);
                         goto err_out;
                 }
+
+                BLOCKING_INIT_NOTIFIER_HEAD(&mbox->notifier);
         }
         return 0;