mmc_get_card 以及 mmc_put_card。
google了一下其實就是把原本mmc_claim_host 以及mmc_release_host加上runtime pm相關的function包起來而成。
[PATCH V3 3/4] mmc: block: Enable runtime pm for mmc blkdevice
從這版patch中可以看到mmc_get_card 以及 mmc_put_card的定義。也取代了原本的mmc_claim_host 以及mmc_release_host。
void mmc_get_card(struct mmc_card *card)
{
pm_runtime_get_sync(&card->dev);
mmc_claim_host(card->host);
}
EXPORT_SYMBOL(mmc_get_card);
/*
* This is a helper function, which releases the host and drops the runtime
* pm reference for the card device.
*/
void mmc_put_card(struct mmc_card *card)
{
mmc_release_host(card->host);
pm_runtime_mark_last_busy(&card->dev);
pm_runtime_put_autosuspend(&card->dev);
}
EXPORT_SYMBOL(mmc_put_card);
從Documentation/power/runtime_pm.txt可以找到這幾個相關function的簡單敘述。
int pm_runtime_get_sync(struct device *dev);
- increment the device's usage counter, run
pm_runtime_resume(dev) and return its result
int pm_runtime_resume(struct device *dev);
- execute the subsystem-level resume callback for the device;
returns 0 on success, 1 if the device's runtime PM status was already 'active'
or error code on failure, where -EAGAIN means it may be safe to attempt to
resume the device again in future, but 'power.runtime_error' should be checked
additionally, and -EACCES means that 'power.disable_depth' is different from 0
void pm_runtime_mark_last_busy(struct device *dev);
- set the power.last_busy field to the current time
int pm_runtime_put_autosuspend(struct device *dev);
- decrement the device's usage counter; if the result is 0 then run
pm_request_autosuspend(dev) and return its result
- set the power.last_busy field to the current time
int pm_runtime_put_autosuspend(struct device *dev);
- decrement the device's usage counter; if the result is 0 then run
pm_request_autosuspend(dev) and return its result
int pm_request_autosuspend(struct device *dev);
- schedule the execution of the subsystem-level suspend callback for the
device when the autosuspend delay has expired; if the delay has already
expired then the work item is queued up immediately
在文件中有下面這麼一段，這邊想提到的是既然mmc_get_card會引用到pm_runtime_resume，根據文件應該在其他地方會先enable runtime pm.
reflects the actual state of the device, its bus type's or its driver's
->probe() callback will likely need to wake it up using one of the PM core's
helper functions described in Section 4. In that case, pm_runtime_resume()
should be used. Of course, for this purpose the device's runtime PM has to be
enabled earlier by calling pm_runtime_enable().
再來文件中提到下面這段，也就理解了為何在mmc_put_card呼叫這兩個function。
Inactivity is determined based on the power.last_busy field. Drivers should
call pm_runtime_mark_last_busy() to update this field after carrying out I/O,
typically just before calling pm_runtime_put_autosuspend().
