Re: [PATCH v10 2/4] uacce: add uacce driver

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Fri, 10 Jan 2020 14:55:39 +0800
"zhangfei.gao@foxmail.com" <zhangfei.gao@foxmail.com> wrote:

> On 2020/1/10 上午1:38, Jonathan Cameron wrote:
> > On Mon, 16 Dec 2019 11:08:15 +0800
> > Zhangfei Gao <zhangfei.gao@linaro.org> wrote:
> >  
> >> From: Kenneth Lee <liguozhu@hisilicon.com>
> >>
> >> Uacce (Unified/User-space-access-intended Accelerator Framework) targets to
> >> provide Shared Virtual Addressing (SVA) between accelerators and processes.
> >> So accelerator can access any data structure of the main cpu.
> >> This differs from the data sharing between cpu and io device, which share
> >> only data content rather than address.
> >> Since unified address, hardware and user space of process can share the
> >> same virtual address in the communication.
> >>
> >> Uacce create a chrdev for every registration, the queue is allocated to
> >> the process when the chrdev is opened. Then the process can access the
> >> hardware resource by interact with the queue file. By mmap the queue
> >> file space to user space, the process can directly put requests to the
> >> hardware without syscall to the kernel space.
> >>
> >> The IOMMU core only tracks mm<->device bonds at the moment, because it
> >> only needs to handle IOTLB invalidation and PASID table entries. However
> >> uacce needs a finer granularity since multiple queues from the same
> >> device can be bound to an mm. When the mm exits, all bound queues must
> >> be stopped so that the IOMMU can safely clear the PASID table entry and
> >> reallocate the PASID.
> >>
> >> An intermediate struct uacce_mm links uacce devices and queues.
> >> Note that an mm may be bound to multiple devices but an uacce_mm
> >> structure only ever belongs to a single device, because we don't need
> >> anything more complex (if multiple devices are bound to one mm, then
> >> we'll create one uacce_mm for each bond).
> >>
> >>          uacce_device --+-- uacce_mm --+-- uacce_queue
> >>                         |              '-- uacce_queue
> >>                         |
> >>                         '-- uacce_mm --+-- uacce_queue
> >>                                        +-- uacce_queue
> >>                                        '-- uacce_queue
> >>
> >> Signed-off-by: Kenneth Lee <liguozhu@hisilicon.com>
> >> Signed-off-by: Zaibo Xu <xuzaibo@huawei.com>
> >> Signed-off-by: Zhou Wang <wangzhou1@hisilicon.com>
> >> Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
> >> Signed-off-by: Zhangfei Gao <zhangfei.gao@linaro.org>  
> > Hi,
> >
> > Two small things I'd missed previously.  Fix those and for
> > what it's worth
> >
> > Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>  
> Thanks Jonathan
> >  
> >> ---
> >>   Documentation/ABI/testing/sysfs-driver-uacce |  37 ++
> >>   drivers/misc/Kconfig                         |   1 +
> >>   drivers/misc/Makefile                        |   1 +
> >>   drivers/misc/uacce/Kconfig                   |  13 +
> >>   drivers/misc/uacce/Makefile                  |   2 +
> >>   drivers/misc/uacce/uacce.c                   | 628 +++++++++++++++++++++++++++
> >>   include/linux/uacce.h                        | 161 +++++++
> >>   include/uapi/misc/uacce/uacce.h              |  38 ++
> >>   8 files changed, 881 insertions(+)
> >>   create mode 100644 Documentation/ABI/testing/sysfs-driver-uacce
> >>   create mode 100644 drivers/misc/uacce/Kconfig
> >>   create mode 100644 drivers/misc/uacce/Makefile
> >>   create mode 100644 drivers/misc/uacce/uacce.c
> >>   create mode 100644 include/linux/uacce.h
> >>   create mode 100644 include/uapi/misc/uacce/uacce.h
> >>  
> > ...  
> >> +
> >> +What:           /sys/class/uacce/<dev_name>/available_instances
> >> +Date:           Dec 2019
> >> +KernelVersion:  5.6
> >> +Contact:        linux-accelerators@lists.ozlabs.org
> >> +Description:    Available instances left of the device
> >> +                Return -ENODEV if uacce_ops get_available_instances is not provided
> >> +  
> > See below.  It doesn't "return" it prints it currently.  
> Will update to
> 'unknown' if uacce_ops get_available_instances is not provided
> >
> > ...
> >  
> >> +static int uacce_fops_mmap(struct file *filep, struct vm_area_struct *vma)
> >> +{
> >> +	struct uacce_queue *q = filep->private_data;
> >> +	struct uacce_device *uacce = q->uacce;
> >> +	struct uacce_qfile_region *qfr;
> >> +	enum uacce_qfrt type = UACCE_MAX_REGION;
> >> +	int ret = 0;
> >> +
> >> +	if (vma->vm_pgoff < UACCE_MAX_REGION)
> >> +		type = vma->vm_pgoff;
> >> +	else
> >> +		return -EINVAL;
> >> +
> >> +	qfr = kzalloc(sizeof(*qfr), GFP_KERNEL);
> >> +	if (!qfr)
> >> +		return -ENOMEM;
> >> +
> >> +	vma->vm_flags |= VM_DONTCOPY | VM_DONTEXPAND | VM_WIPEONFORK;
> >> +	vma->vm_ops = &uacce_vm_ops;
> >> +	vma->vm_private_data = q;
> >> +	qfr->type = type;
> >> +
> >> +	mutex_lock(&uacce_mutex);
> >> +
> >> +	if (q->state != UACCE_Q_INIT && q->state != UACCE_Q_STARTED) {
> >> +		ret = -EINVAL;
> >> +		goto out_with_lock;
> >> +	}
> >> +
> >> +	if (q->qfrs[type]) {
> >> +		ret = -EEXIST;
> >> +		goto out_with_lock;
> >> +	}
> >> +
> >> +	switch (type) {
> >> +	case UACCE_QFRT_MMIO:
> >> +		if (!uacce->ops->mmap) {
> >> +			ret = -EINVAL;
> >> +			goto out_with_lock;
> >> +		}
> >> +
> >> +		ret = uacce->ops->mmap(q, vma, qfr);
> >> +		if (ret)
> >> +			goto out_with_lock;
> >> +
> >> +		break;
> >> +
> >> +	case UACCE_QFRT_DUS:
> >> +		if (uacce->flags & UACCE_DEV_SVA) {
> >> +			if (!uacce->ops->mmap) {
> >> +				ret = -EINVAL;
> >> +				goto out_with_lock;
> >> +			}
> >> +
> >> +			ret = uacce->ops->mmap(q, vma, qfr);
> >> +			if (ret)
> >> +				goto out_with_lock;
> >> +		}  
> > Slightly odd corner case, but what stops us getting here with
> > the UACCE_DEV_SVA flag not set?  If that happened I'd expect to
> > return an error but looks like we return 0.  
> The check with flag UACCE_DEV_SVA can be removed here, non-sva also has 
> dus region.
> We have removed the check when we add non-sva support.
> > ...
> >  
> >> +static ssize_t available_instances_show(struct device *dev,
> >> +					struct device_attribute *attr,
> >> +					char *buf)
> >> +{
> >> +	struct uacce_device *uacce = to_uacce_device(dev);
> >> +	int val = -ENODEV;
> >> +
> >> +	if (uacce->ops->get_available_instances)
> >> +		val = uacce->ops->get_available_instances(uacce);
> >> +
> >> +	return sprintf(buf, "%d\n", val);  
> > It's unusual to pass an error value back as a string.
> > I'd expect some logic like..
> >
> > 	if (val < 0)
> > 		return val;
> >
> > 	return sprintf(buf, "%d\n", val);
> >
> > Note this is the documented behavior "returns -ENODEV".  
> If return -ENODEV,
> cat /sys/class/uacce/hisi_zip-0/available_instances
> cat: /sys/class/uacce/hisi_zip-0/available_instances: No such device
> 
> I think print "unknown" maybe better, like cpufreq.c
> 
>          if (uacce->ops->get_available_instances)
>                  return sprintf(buf, "%d\n",
> uacce->ops->get_available_instances(uacce));
> 
>          return sprintf(buf, "unknown\n");

From userspace code point a simple error code return is better than
a 'magic' string in the file.

You'll find people just try to read an integer without checking
for unknown and hence get a very odd result. Much better to throw
them an error code.

Jonathan


> 
> Thanks
> 
> 
>