Switch the tx_lock to a spinlock we allow clients to use rpmsg_trysend()
from atomic context.

In order to allow clients to sleep while waiting for space in the FIFO
we release the lock temporarily around the delay; which should be
replaced by sending a READ_NOTIF and waiting for the remote to signal
us that space has been made available.

Signed-off-by: Bjorn Andersson <bjorn.anders...@linaro.org>
---
 drivers/rpmsg/qcom_glink_native.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/rpmsg/qcom_glink_native.c 
b/drivers/rpmsg/qcom_glink_native.c
index e0f31ed096a5..6e950e9afa82 100644
--- a/drivers/rpmsg/qcom_glink_native.c
+++ b/drivers/rpmsg/qcom_glink_native.c
@@ -113,7 +113,7 @@ struct qcom_glink {
        spinlock_t rx_lock;
        struct list_head rx_queue;
 
-       struct mutex tx_lock;
+       spinlock_t tx_lock;
 
        spinlock_t idr_lock;
        struct idr lcids;
@@ -288,15 +288,14 @@ static int qcom_glink_tx(struct qcom_glink *glink,
                         const void *data, size_t dlen, bool wait)
 {
        unsigned int tlen = hlen + dlen;
+       unsigned long flags;
        int ret;
 
        /* Reject packets that are too big */
        if (tlen >= glink->tx_pipe->length)
                return -EINVAL;
 
-       ret = mutex_lock_interruptible(&glink->tx_lock);
-       if (ret)
-               return ret;
+       spin_lock_irqsave(&glink->tx_lock, flags);
 
        while (qcom_glink_tx_avail(glink) < tlen) {
                if (!wait) {
@@ -304,7 +303,12 @@ static int qcom_glink_tx(struct qcom_glink *glink,
                        goto out;
                }
 
+               /* Wait without holding the tx_lock */
+               spin_unlock_irqrestore(&glink->tx_lock, flags);
+
                usleep_range(10000, 15000);
+
+               spin_lock_irqsave(&glink->tx_lock, flags);
        }
 
        qcom_glink_tx_write(glink, hdr, hlen, data, dlen);
@@ -313,7 +317,7 @@ static int qcom_glink_tx(struct qcom_glink *glink,
        mbox_client_txdone(glink->mbox_chan, 0);
 
 out:
-       mutex_unlock(&glink->tx_lock);
+       spin_unlock_irqrestore(&glink->tx_lock, flags);
 
        return ret;
 }
@@ -1567,7 +1571,7 @@ struct qcom_glink *qcom_glink_native_probe(struct device 
*dev,
        glink->features = features;
        glink->intentless = intentless;
 
-       mutex_init(&glink->tx_lock);
+       spin_lock_init(&glink->tx_lock);
        spin_lock_init(&glink->rx_lock);
        INIT_LIST_HEAD(&glink->rx_queue);
        INIT_WORK(&glink->rx_work, qcom_glink_work);
-- 
2.15.0

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