spi-sync-irqsafe.c

static void mcp23s17_read_irqsafe_complete(void *context)
{
        struct mcp23s08 *mcp = context;
        spin_unlock_irqrestore(&mcp->slock, mcp->irq_flags);
}

static int mcp23s17_read_irqsafe(struct mcp23s08 *mcp, unsigned reg)
{
        unsigned long flags;
        struct spi_device *spi = mcp->data;
        struct spi_transfer t[2] = {
                [0] = {
                        .tx_buf = mcp->tx,
                        .len    = 2,
                },
                [1] = {
                        .rx_buf = mcp->rx,
                        .len    = 2,
                },
        };

        memset(mcp->tx, '\0', sizeof(mcp->tx));
        memset(mcp->rx, '\0', sizeof(mcp->rx));
        mcp->tx[0] = mcp->addr | 0x01;
        mcp->tx[1] = reg << 1;
        spi_message_init(&mcp->msg);
        spi_message_add_tail(&t[0], &mcp->msg);
        spi_message_add_tail(&t[1], &mcp->msg);
        mcp->msg.complete = mcp23s17_read_irqsafe_complete;
        mcp->msg.context  = mcp;

        spin_lock_irqsave(&mcp->slock, mcp->irq_flags); /* lock */
        spi_async_locked(spi, &mcp->msg);   /* call async */
        spin_lock_irqsave(&mcp->slock, flags);  /* wait */
        spin_unlock_irqrestore(&mcp->slock, flags); /* unlock previous line*/
        return (mcp->msg.status == 0 ? ((mcp->rx[0] | (mcp->rx[1] << 8))) : -1);
}