On Thu, 5 May 2022 15:10:43 +0530 Abhishek Sahu <abhsahu@xxxxxxxxxx> wrote: > On 5/5/2022 1:12 AM, Alex Williamson wrote: > > On Mon, 25 Apr 2022 14:56:13 +0530 > > Abhishek Sahu <abhsahu@xxxxxxxxxx> wrote: > > > >> The vfio/pci driver will have runtime power management support where the > >> user can put the device low power state and then PCI devices can go into > >> the D3cold state. If the device is in low power state and user issues any > >> IOCTL, then the device should be moved out of low power state first. Once > >> the IOCTL is serviced, then it can go into low power state again. The > >> runtime PM framework manages this with help of usage count. One option > >> was to add the runtime PM related API's inside vfio/pci driver but some > >> IOCTL (like VFIO_DEVICE_FEATURE) can follow a different path and more > >> IOCTL can be added in the future. Also, the runtime PM will be > >> added for vfio/pci based drivers variant currently but the other vfio > >> based drivers can use the same in the future. So, this patch adds the > >> runtime calls runtime related API in the top level IOCTL function itself. > >> > >> For the vfio drivers which do not have runtime power management support > >> currently, the runtime PM API's won't be invoked. Only for vfio/pci > >> based drivers currently, the runtime PM API's will be invoked to increment > >> and decrement the usage count. Taking this usage count incremented while > >> servicing IOCTL will make sure that user won't put the device into low > >> power state when any other IOCTL is being serviced in parallel. > >> > >> Signed-off-by: Abhishek Sahu <abhsahu@xxxxxxxxxx> > >> --- > >> drivers/vfio/vfio.c | 44 +++++++++++++++++++++++++++++++++++++++++--- > >> 1 file changed, 41 insertions(+), 3 deletions(-) > >> > >> diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c > >> index a4555014bd1e..4e65a127744e 100644 > >> --- a/drivers/vfio/vfio.c > >> +++ b/drivers/vfio/vfio.c > >> @@ -32,6 +32,7 @@ > >> #include <linux/vfio.h> > >> #include <linux/wait.h> > >> #include <linux/sched/signal.h> > >> +#include <linux/pm_runtime.h> > >> #include "vfio.h" > >> > >> #define DRIVER_VERSION "0.3" > >> @@ -1536,6 +1537,30 @@ static const struct file_operations vfio_group_fops = { > >> .release = vfio_group_fops_release, > >> }; > >> > >> +/* > >> + * Wrapper around pm_runtime_resume_and_get(). > >> + * Return 0, if driver power management callbacks are not present i.e. the driver is not > > > > Mind the gratuitous long comment line here. > > > > Thanks Alex. > > That was a miss. I will fix this. > > >> + * using runtime power management. > >> + * Return 1 upon success, otherwise -errno > > > > Changing semantics vs the thing we're wrapping, why not provide a > > wrapper for the `put` as well to avoid? The only cases where we return > > zero are just as easy to detect on the other side. > > > > Yes. Using wrapper function for put is better option. > I will make the changes. > > >> + */ > >> +static inline int vfio_device_pm_runtime_get(struct device *dev) > > > > Given some of Jason's recent series, this should probably just accept a > > vfio_device. > > > > Sorry. I didn't get this part. > > Do I need to change it to > > static inline int vfio_device_pm_runtime_get(struct vfio_device *device) > { > struct device *dev = device->dev; > ... > } Yes. > >> +{ > >> +#ifdef CONFIG_PM > >> + int ret; > >> + > >> + if (!dev->driver || !dev->driver->pm) > >> + return 0; I'm also wondering how we could ever get here with dev->driver == NULL. If that were actually possible, the above would at best be racy. It also really seems like there ought to be a better test than the driver->pm pointer to check if runtime pm is enabled, but I haven't spotted it yet. > >> + > >> + ret = pm_runtime_resume_and_get(dev); > >> + if (ret < 0) > >> + return ret; > >> + > >> + return 1; > >> +#else > >> + return 0; > >> +#endif > >> +} > >> + > >> /* > >> * VFIO Device fd > >> */ > >> @@ -1845,15 +1870,28 @@ static long vfio_device_fops_unl_ioctl(struct file *filep, > >> unsigned int cmd, unsigned long arg) > >> { > >> struct vfio_device *device = filep->private_data; > >> + int pm_ret, ret = 0; > >> + > >> + pm_ret = vfio_device_pm_runtime_get(device->dev); > >> + if (pm_ret < 0) > >> + return pm_ret; > > > > I wonder if we might simply want to mask pm errors behind -EIO, maybe > > with a rate limited dev_info(). My concern would be that we might mask > > errnos that userspace has come to expect for certain ioctls. Thanks, > > > > Alex > > > > I need to do something like following. Correct ? > > ret = vfio_device_pm_runtime_get(device); > if (ret < 0) { > dev_info_ratelimited(device->dev, "vfio: runtime resume failed %d\n", ret); > return -EIO; > } Yeah, though I'd welcome other thoughts here. I don't necessarily like the idea of squashing the errno, but at the same time, if pm_runtime_resume_and_get() returns -EINVAL on user ioctl, that's not really describing an invalid parameter relative to the ioctl itself. Thanks, Alex