stm class: Add runtime power management handling

Currently, there's no runtime pm in stm class devices, which makes it
harder for the underlying hardware drivers to handle their power
management.

This patch applies the following runtime pm policy to stm class devices,
which their parents can rely on for their power management tracking:

  * device is in use during character device writes,
  * delayed autosuspend is used to keep it active between adjacent
  writes,
  * device is in use while mmio regions are mapped,
  * device is is use while any stm_source devices are linked to it.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Chunyan Zhang <zhang.chunyan@linaro.org>

drivers/hwtracing/stm/core.c

@@ -15,6 +15,7 @@
  * as defined in MIPI STPv2 specification.
  */
 
+#include <linux/pm_runtime.h>
 #include <linux/uaccess.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
@@ -482,14 +483,40 @@ static ssize_t stm_char_write(struct file *file, const char __user *buf,
 		return -EFAULT;
 	}
 
+	pm_runtime_get_sync(&stm->dev);
+
 	count = stm_write(stm->data, stmf->output.master, stmf->output.channel,
 			  kbuf, count);
 
+	pm_runtime_mark_last_busy(&stm->dev);
+	pm_runtime_put_autosuspend(&stm->dev);
 	kfree(kbuf);
 
 	return count;
 }
 
+static void stm_mmap_open(struct vm_area_struct *vma)
+{
+	struct stm_file *stmf = vma->vm_file->private_data;
+	struct stm_device *stm = stmf->stm;
+
+	pm_runtime_get(&stm->dev);
+}
+
+static void stm_mmap_close(struct vm_area_struct *vma)
+{
+	struct stm_file *stmf = vma->vm_file->private_data;
+	struct stm_device *stm = stmf->stm;
+
+	pm_runtime_mark_last_busy(&stm->dev);
+	pm_runtime_put_autosuspend(&stm->dev);
+}
+
+static const struct vm_operations_struct stm_mmap_vmops = {
+	.open	= stm_mmap_open,
+	.close	= stm_mmap_close,
+};
+
 static int stm_char_mmap(struct file *file, struct vm_area_struct *vma)
 {
 	struct stm_file *stmf = file->private_data;
@@ -514,8 +541,11 @@ static int stm_char_mmap(struct file *file, struct vm_area_struct *vma)
 	if (!phys)
 		return -EINVAL;
 
+	pm_runtime_get_sync(&stm->dev);
+
 	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
 	vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
+	vma->vm_ops = &stm_mmap_vmops;
 	vm_iomap_memory(vma, phys, size);
 
 	return 0;
@@ -701,6 +731,17 @@ int stm_register_device(struct device *parent, struct stm_data *stm_data,
 	if (err)
 		goto err_device;
 
+	/*
+	 * Use delayed autosuspend to avoid bouncing back and forth
+	 * on recurring character device writes, with the initial
+	 * delay time of 2 seconds.
+	 */
+	pm_runtime_no_callbacks(&stm->dev);
+	pm_runtime_use_autosuspend(&stm->dev);
+	pm_runtime_set_autosuspend_delay(&stm->dev, 2000);
+	pm_runtime_set_suspended(&stm->dev);
+	pm_runtime_enable(&stm->dev);
+
 	return 0;
 
 err_device:
@@ -724,6 +765,9 @@ void stm_unregister_device(struct stm_data *stm_data)
 	struct stm_source_device *src, *iter;
 	int i, ret;
 
+	pm_runtime_dont_use_autosuspend(&stm->dev);
+	pm_runtime_disable(&stm->dev);
+
 	mutex_lock(&stm->link_mutex);
 	list_for_each_entry_safe(src, iter, &stm->link_list, link_entry) {
 		ret = __stm_source_link_drop(src, stm);
@@ -878,6 +922,8 @@ static int __stm_source_link_drop(struct stm_source_device *src,
 
 	stm_output_free(link, &src->output);
 	list_del_init(&src->link_entry);
+	pm_runtime_mark_last_busy(&link->dev);
+	pm_runtime_put_autosuspend(&link->dev);
 	/* matches stm_find_device() from stm_source_link_store() */
 	stm_put_device(link);
 	rcu_assign_pointer(src->link, NULL);
@@ -971,8 +1017,11 @@ static ssize_t stm_source_link_store(struct device *dev,
 	if (!link)
 		return -EINVAL;
 
+	pm_runtime_get(&link->dev);
+
 	err = stm_source_link_add(src, link);
 	if (err) {
+		pm_runtime_put_autosuspend(&link->dev);
 		/* matches the stm_find_device() above */
 		stm_put_device(link);
 	}
@@ -1033,6 +1082,9 @@ int stm_source_register_device(struct device *parent,
 	if (err)
 		goto err;
 
+	pm_runtime_no_callbacks(&src->dev);
+	pm_runtime_forbid(&src->dev);
+
 	err = device_add(&src->dev);
 	if (err)
 		goto err;