Re: [PATCH] fpga: dfl: support multiple opens on feature device node.

From: Xu Yilum
Date: Mon Dec 30 2019 - 02:36:17 EST

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Hi Moritz:

Do you have more concern on this patch?

I've sent a patch v2 for this, fixed minor inline comments.

Thanks.

On Tue, Dec 10, 2019 at 04:54:36PM +0800, Xu Yilun wrote:
> On Mon, Dec 09, 2019 at 06:06:54PM -0800, Moritz Fischer wrote:
> > Hi Xu,
> >
> > Sorry for the delay.
> >
> > On Mon, Nov 18, 2019 at 01:20:41PM +0800, Xu Yilun wrote:
> > > Each DFL functional block, e.g. AFU (Accelerated Function Unit) and FME
> > > (FPGA Management Engine), could implement more than one function within
> > > its region, but current driver only allows one user application to access
> > > it by exclusive open on device node. So this is not convenient and
> > > flexible for userspace applications, as they have to combine lots of
> > > different functions into one single application.
> > I'm not entirely sure how I feel about that, wouldn't the right solution
> > be to create more devices? If this ends up being 100% passthrough
> > basically, VFIO would be a better choice?
>
> The major issue we want to resolve is how to access the same accelerator by
> multiple applications. As you know, the accelerator is the dynamic region (AFU)
> defined by end user, so we don't know how many sub functions end user will
> implement in the one dynamic region (AFU) of FPGA. So driver can't create devices
> for logic blocks implemented inside dynamic region.
>
> We don't want 100% passthrough, but only dynamic region (AFU), because for static
> region part, we can reuse everything, including hardware logics, kernel drivers and
> upper layer stack/lib/app/tools. Use VFIO PCI directly may not be helpful for our case,
> and make the device node to support multiple open seems the simplest solution.
>
> > >
> > > This patch removes the limitation here to allow multiple opens to each
> > > feature device node for AFU and FME from userspace applications. If user
> > > still needs exclusive access to these device node, O_EXCL flag must be
> > > issued together with open.
> > Wouldn't you wanna default to have exclusive access, and then allow
> > multiple opens by means of a management interface, maybe?
>
> I see some examples here which is using O_EXCL flag to indicate exclusive open,
> like nvram misc driver. I feel this may be a regular method to follow, I believe
> if we can save one userspace interface with this, that will be simpler for users
> too.
>
> > >
> > > Signed-off-by: Wu Hao <hao.wu@xxxxxxxxx>
> > > Signed-off-by: Xu Yilun <yilun.xu@xxxxxxxxx>
> > > ---
> > > drivers/fpga/dfl-afu-main.c | 26 +++++++++++++++-----------
> > > drivers/fpga/dfl-fme-main.c | 19 ++++++++++++-------
> > > drivers/fpga/dfl.c | 15 +++++++++++++--
> > > drivers/fpga/dfl.h | 35 +++++++++++++++++++++++++++--------
> > > 4 files changed, 67 insertions(+), 28 deletions(-)
> > >
> > > diff --git a/drivers/fpga/dfl-afu-main.c b/drivers/fpga/dfl-afu-main.c
> > > index e4a34dc..c6e0e07 100644
> > > --- a/drivers/fpga/dfl-afu-main.c
> > > +++ b/drivers/fpga/dfl-afu-main.c
> > > @@ -561,14 +561,16 @@ static int afu_open(struct inode *inode, struct file *filp)
> > > if (WARN_ON(!pdata))
> > > return -ENODEV;
> > >
> > > - ret = dfl_feature_dev_use_begin(pdata);
> > > - if (ret)
> > > - return ret;
> > > -
> > > - dev_dbg(&fdev->dev, "Device File Open\n");
> > > - filp->private_data = fdev;
> > > + mutex_lock(&pdata->lock);
> > > + ret = dfl_feature_dev_use_begin(pdata, filp->f_flags & O_EXCL);
> > > + if (!ret) {
> > > + dev_dbg(&fdev->dev, "Device File Opened %d Times\n",
> > > + dfl_feature_dev_use_count(pdata));
> > Could those be trace events instead?
>
> I investigated a little to see how we use trace to get this info.
> 1. config PROFILE_ANNOTATED_BRANCHES in kernel, and add likely()/unlikely()
> for ret judgement. This adds some overhead to system.
> 2. config CONFIG_PROFILE_ALL_BRANCHES, no code change here. This adds
> great overhead to system.
> 3. write a dedicated trace event for this count. I think this is a little
> too heavy, we need to add extra file for it, but this count is just
> minor info to the driver.
>
> What's your suggestion for this? Could we just leave the print here for
> simplicity.
>
>
> > > + filp->private_data = fdev;
> > > + }
> > > + mutex_unlock(&pdata->lock);
> > >
> > > - return 0;
> > > + return ret;
> > > }
> > >
> > > static int afu_release(struct inode *inode, struct file *filp)
> > > @@ -581,12 +583,14 @@ static int afu_release(struct inode *inode, struct file *filp)
> > > pdata = dev_get_platdata(&pdev->dev);
> > >
> > > mutex_lock(&pdata->lock);
> > > - __port_reset(pdev);
> > > - afu_dma_region_destroy(pdata);
> > > - mutex_unlock(&pdata->lock);
> > > -
> > > dfl_feature_dev_use_end(pdata);
> > >
> > > + if (!dfl_feature_dev_use_count(pdata)) {
> > > + __port_reset(pdev);
> > > + afu_dma_region_destroy(pdata);
> > > + }
> > > + mutex_unlock(&pdata->lock);
> > > +
> > > return 0;
> > > }
> > >
> > > diff --git a/drivers/fpga/dfl-fme-main.c b/drivers/fpga/dfl-fme-main.c
> > > index 7c930e6..fda8623 100644
> > > --- a/drivers/fpga/dfl-fme-main.c
> > > +++ b/drivers/fpga/dfl-fme-main.c
> > > @@ -600,14 +600,16 @@ static int fme_open(struct inode *inode, struct file *filp)
> > > if (WARN_ON(!pdata))
> > > return -ENODEV;
> > >
> > > - ret = dfl_feature_dev_use_begin(pdata);
> > > - if (ret)
> > > - return ret;
> > > -
> > > - dev_dbg(&fdev->dev, "Device File Open\n");
> > > - filp->private_data = pdata;
> > > + mutex_lock(&pdata->lock);
> > > + ret = dfl_feature_dev_use_begin(pdata, filp->f_flags & O_EXCL);
> > > + if (!ret) {
> > > + dev_dbg(&fdev->dev, "Device File Opened %d Times\n",
> > > + dfl_feature_dev_use_count(pdata));
> > > + filp->private_data = pdata;
> > > + }
> > > + mutex_unlock(&pdata->lock);
> > >
> > > - return 0;
> > > + return ret;
> > > }
> > >
> > > static int fme_release(struct inode *inode, struct file *filp)
> > > @@ -616,7 +618,10 @@ static int fme_release(struct inode *inode, struct file *filp)
> > > struct platform_device *pdev = pdata->dev;
> > >
> > > dev_dbg(&pdev->dev, "Device File Release\n");
> > > +
> > > + mutex_lock(&pdata->lock);
> > > dfl_feature_dev_use_end(pdata);
> > > + mutex_unlock(&pdata->lock);
> > >
> > > return 0;
> > > }
> > > diff --git a/drivers/fpga/dfl.c b/drivers/fpga/dfl.c
> > > index 96a2b82..9909948 100644
> > > --- a/drivers/fpga/dfl.c
> > > +++ b/drivers/fpga/dfl.c
> > > @@ -1079,6 +1079,7 @@ static int __init dfl_fpga_init(void)
> > > */
> > > int dfl_fpga_cdev_release_port(struct dfl_fpga_cdev *cdev, int port_id)
> > > {
> > > + struct dfl_feature_platform_data *pdata;
> > > struct platform_device *port_pdev;
> > > int ret = -ENODEV;
> > >
> > > @@ -1093,7 +1094,11 @@ int dfl_fpga_cdev_release_port(struct dfl_fpga_cdev *cdev, int port_id)
> > > goto put_dev_exit;
> > > }
> > >
> > > - ret = dfl_feature_dev_use_begin(dev_get_platdata(&port_pdev->dev));
> > > + pdata = dev_get_platdata(&port_pdev->dev);
> > > +
> > > + mutex_lock(&pdata->lock);
> > > + ret = dfl_feature_dev_use_begin(pdata, true);
> > > + mutex_unlock(&pdata->lock);
> > > if (ret)
> > > goto put_dev_exit;
> > >
> > > @@ -1120,6 +1125,7 @@ EXPORT_SYMBOL_GPL(dfl_fpga_cdev_release_port);
> > > */
> > > int dfl_fpga_cdev_assign_port(struct dfl_fpga_cdev *cdev, int port_id)
> > > {
> > > + struct dfl_feature_platform_data *pdata;
> > > struct platform_device *port_pdev;
> > > int ret = -ENODEV;
> > >
> > > @@ -1138,7 +1144,12 @@ int dfl_fpga_cdev_assign_port(struct dfl_fpga_cdev *cdev, int port_id)
> > > if (ret)
> > > goto put_dev_exit;
> > >
> > > - dfl_feature_dev_use_end(dev_get_platdata(&port_pdev->dev));
> > > + pdata = dev_get_platdata(&port_pdev->dev);
> > > +
> > > + mutex_lock(&pdata->lock);
> > > + dfl_feature_dev_use_end(pdata);
> > > + mutex_unlock(&pdata->lock);
> > > +
> > > cdev->released_port_num--;
> > > put_dev_exit:
> > > put_device(&port_pdev->dev);
> > > diff --git a/drivers/fpga/dfl.h b/drivers/fpga/dfl.h
> > > index 9f0e656..4a9a33c 100644
> > > --- a/drivers/fpga/dfl.h
> > > +++ b/drivers/fpga/dfl.h
> > > @@ -205,8 +205,6 @@ struct dfl_feature {
> > > const struct dfl_feature_ops *ops;
> > > };
> > >
> > > -#define DEV_STATUS_IN_USE 0
> > > -
> > > #define FEATURE_DEV_ID_UNUSED (-1)
> > >
> > > /**
> > > @@ -219,8 +217,9 @@ struct dfl_feature {
> > > * @dfl_cdev: ptr to container device.
> > > * @id: id used for this feature device.
> > > * @disable_count: count for port disable.
> > > + * @excl_open: set on feature device exclusive open.
> > > + * @open_count: count for feature device open.
> > > * @num: number for sub features.
> > > - * @dev_status: dev status (e.g. DEV_STATUS_IN_USE).
> > > * @private: ptr to feature dev private data.
> > > * @features: sub features of this feature dev.
> > > */
> > > @@ -232,26 +231,46 @@ struct dfl_feature_platform_data {
> > > struct dfl_fpga_cdev *dfl_cdev;
> > > int id;
> > > unsigned int disable_count;
> > > - unsigned long dev_status;
> > > + bool excl_open;
> > > + int open_count;
> > > void *private;
> > > int num;
> > > struct dfl_feature features[0];
> > > };
> > >
> > > static inline
> >
> > > -int dfl_feature_dev_use_begin(struct dfl_feature_platform_data *pdata)
> > > +int dfl_feature_dev_use_begin(struct dfl_feature_platform_data *pdata,
> > > + bool excl)
> > > {
> > > - /* Test and set IN_USE flags to ensure file is exclusively used */
> > > - if (test_and_set_bit_lock(DEV_STATUS_IN_USE, &pdata->dev_status))
> > > + if (pdata->excl_open)
> > > return -EBUSY;
> > >
> > > + if (excl) {
> > > + if (pdata->open_count)
> > > + return -EBUSY;
> > > +
> > > + pdata->excl_open = true;
> > > + }
> > > + pdata->open_count++;
> > > +
> > > return 0;
> > > }
> > >
> > > static inline
> > > void dfl_feature_dev_use_end(struct dfl_feature_platform_data *pdata)
> > > {
> > > - clear_bit_unlock(DEV_STATUS_IN_USE, &pdata->dev_status);
> > > + pdata->excl_open = false;
> > > +
> > > + if (WARN_ON(pdata->open_count <= 0))
> > > + return;
> > > +
> > > + pdata->open_count--;
> > > +}
> > > +
> > > +static inline
> > Feel free to drop the inline here. Your compiler will figure that out by
> > iteself.
>
> Yes I'll change it.
>
> > > +int dfl_feature_dev_use_count(struct dfl_feature_platform_data *pdata)
> > > +{
> > > + return pdata->open_count;
> > > }
> > >
> > > static inline
> > > --
> > > 2.7.4
> > >
> >
> > Again, sorry for the delay,
> >
> > Moritz
>
> Thanks for take your time out :)
>
> Yilun

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