+static ssize_t cs_char_read(struct file *file, char __user *buf, size_t count,
+								loff_t *unused)
+{
+	struct cs_char *csdata = file->private_data;
+	u32 data;
+	ssize_t retval;
+
+	if (count < sizeof(data))
+		return -EINVAL;
+
+	for ( ; ; ) {
+		DEFINE_WAIT(wait);
+
+		spin_lock_bh(&csdata->lock);
+		if (!list_empty(&csdata->chardev_queue)) {
+			data = cs_pop_entry(&csdata->chardev_queue);
+		} else if (!list_empty(&csdata->dataind_queue)) {
+			data = cs_pop_entry(&csdata->dataind_queue);
+			--csdata->dataind_pending;
+
+		} else {
+			data = 0;
+		}
+		spin_unlock_bh(&csdata->lock);
+
+		if (data)
+			break;
+		if (file->f_flags & O_NONBLOCK) {
+			retval = -EAGAIN;
+			goto out;
+		} else if (signal_pending(current)) {
+			retval = -ERESTARTSYS;
+			goto out;
+		}
+		prepare_to_wait_exclusive(&csdata->wait, &wait,
+						TASK_INTERRUPTIBLE);
+		schedule();
+		finish_wait(&csdata->wait, &wait);
+	}
+
+	retval = put_user(data, (u32 __user *)buf);
+	if (!retval)
+		retval = sizeof(data);
+
+out:
+	return retval;
+}
+
+static ssize_t cs_char_write(struct file *file, const char __user *buf,
+						size_t count, loff_t *unused)
+{
+	struct cs_char *csdata = file->private_data;
+	u32 data;
+	int err;
+	ssize_t	retval;
+
+	if (count < sizeof(data))
+		return -EINVAL;
+
+	if (get_user(data, (u32 __user *)buf))
+		retval = -EFAULT;
+	else
+		retval = count;

You want to execute the command even if you got -EFAULT?
That is highly unusual.

+
+	err = cs_hsi_command(csdata->hi, data);
+	if (err < 0)
+		retval = err;
+
+	return retval;
+}
+
+static long cs_char_ioctl(struct file *file, unsigned int cmd,
+				unsigned long arg)
+{
+	struct cs_char *csdata = file->private_data;
+	int r = 0;
+
+	switch (cmd) {
+	case CS_GET_STATE: {
+		unsigned int state;
+
+		state = cs_hsi_get_state(csdata->hi);
+		if (copy_to_user((void __user *)arg, &state, sizeof(state)))
+			r = -EFAULT;
+	}
+		break;
+	case CS_SET_WAKELINE: {
+		unsigned int state;
+
+		if (copy_from_user(&state, (void __user *)arg, sizeof(state)))
+			r = -EFAULT;
+		else
+			cs_hsi_set_wakeline(csdata->hi, state);

No sanity checking for state?

+	}
+		break;
+	case CS_GET_IF_VERSION: {
+		unsigned int ifver = CS_IF_VERSION;
+
+		if (copy_to_user((void __user *)arg, &ifver, sizeof(ifver)))
+			r = -EFAULT;
+		break;
+	}
+	case CS_CONFIG_BUFS: {
+		struct cs_buffer_config buf_cfg;
+
+		if (copy_from_user(&buf_cfg, (void __user *)arg,
+							sizeof(buf_cfg)))
+			r = -EFAULT;
+		else
+			r = cs_hsi_buf_config(csdata->hi, &buf_cfg);

Sanity checking?

+		break;
+	}
+	default:
+		r = -ENOTTY;
+		break;
+	}
+
+	return r;
+}
+
+static int cs_char_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	if (vma->vm_end < vma->vm_start)
+		return -EINVAL;
+
+	if (((vma->vm_end - vma->vm_start) >> PAGE_SHIFT) != 1)
+		return -EINVAL;
+
+	vma->vm_flags |= VM_RESERVED;
+	vma->vm_ops = &cs_char_vm_ops;
+	vma->vm_private_data = file->private_data;
+
+	return 0;
+}
+
+static int cs_char_open(struct inode *unused, struct file *file)
+{
+	int ret = 0;
+
+	spin_lock_bh(&cs_char_data.lock);
+	if (cs_char_data.opened) {
+		ret = -EBUSY;
+		spin_unlock_bh(&cs_char_data.lock);
+		goto out;
+	}
+	cs_char_data.mmap_base = get_zeroed_page(GFP_ATOMIC);

This could be moved outside the locked sectionand use GFP_KERNEL.

+	if (!cs_char_data.mmap_base) {
+		dev_err(&cs_char_data.cl->device,
+					"Shared memory allocation failed.\n");
+		ret = -ENOMEM;
+		spin_unlock_bh(&cs_char_data.lock);
+		goto out;
+	}
+	cs_char_data.mmap_size = CS_MMAP_SIZE;
+	cs_char_data.dataind_pending = 0;
+	cs_char_data.opened = 1;
+	file->private_data = &cs_char_data;
+	spin_unlock_bh(&cs_char_data.lock);
+
+	BUG_ON(cs_char_data.hi);
+
+	ret = cs_hsi_start(&cs_char_data.hi, cs_char_data.cl,
+				cs_char_data.mmap_base, cs_char_data.mmap_size);
+	if (ret) {
+		dev_err(&cs_char_data.cl->device, "Unable to initialize HSI\n");
+		free_page(cs_char_data.mmap_base);
+		goto out;
+	}
+
+out:
+	return ret;
+}