linux-kernel - Re: [RFC PATCH v2 2/3] accel: add dedicated minor for accelerator devices

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Message-ID: <CAFCwf10SLEd3dKXYEhyX0E95b66Qfok2Rou=6tOE_j2LCpOc6A@mail.gmail.com>
Date:   Sun, 6 Nov 2022 12:51:51 +0200
From:   Oded Gabbay <ogabbay@...nel.org>
To:     Jeffrey Hugo <quic_jhugo@...cinc.com>
Cc:     David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Jason Gunthorpe <jgg@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        Alex Deucher <alexander.deucher@....com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Yuji Ishikawa <yuji2.ishikawa@...hiba.co.jp>,
        Jiho Chu <jiho.chu@...sung.com>,
        Daniel Stone <daniel@...ishbar.org>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Hilman <khilman@...libre.com>,
        Jagan Teki <jagan@...rulasolutions.com>,
        Jacek Lawrynowicz <jacek.lawrynowicz@...ux.intel.com>,
        Maciej Kwapulinski <maciej.kwapulinski@...ux.intel.com>
Subject: Re: [RFC PATCH v2 2/3] accel: add dedicated minor for accelerator devices

On Wed, Nov 2, 2022 at 11:17 PM Jeffrey Hugo <quic_jhugo@...cinc.com> wrote:
>
> On 11/2/2022 2:34 PM, Oded Gabbay wrote:
> > @@ -24,16 +33,6 @@ static char *accel_devnode(struct device *dev, umode_t *mode)
> >
> >   static CLASS_ATTR_STRING(accel_version, 0444, "accel 1.0.0 20221018");
> >
> > -/**
> > - * accel_sysfs_init - initialize sysfs helpers
> > - *
> > - * This is used to create the ACCEL class, which is the implicit parent of any
> > - * other top-level ACCEL sysfs objects.
> > - *
> > - * You must call accel_sysfs_destroy() to release the allocated resources.
> > - *
> > - * Return: 0 on success, negative error code on failure.
> > - */
>
> Why are we removing this?
It should have been removed at the first patch, and will be fixed in v3.
I'm removing it as it is a static function. We don't document every
static function.
>
> >   static int accel_sysfs_init(void)
> >   {
> >       int err;
> > @@ -54,11 +53,6 @@ static int accel_sysfs_init(void)
> >       return 0;
> >   }
> >
> > -/**
> > - * accel_sysfs_destroy - destroys ACCEL class
> > - *
> > - * Destroy the ACCEL device class.
> > - */
>
> Again, why remove this?  Adding it in one patch than immediately
> removing it in the next patch seems wasteful.
Correct, will be removed from the first patch in the next version.
>
> >   static void accel_sysfs_destroy(void)
> >   {
> >       if (IS_ERR_OR_NULL(accel_class))
> > @@ -68,11 +62,185 @@ static void accel_sysfs_destroy(void)
> >       accel_class = NULL;
> >   }
> >
> > +static void accel_minor_release(struct drm_minor *minor)
> > +{
> > +     drm_dev_put(minor->dev);
> > +}
> > +
> > +/**
> > + * accel_open - open method for ACCEL file
> > + * @inode: device inode
> > + * @filp: file pointer.
> > + *
> > + * This function must be used by drivers as their &file_operations.open method.
>
> Feels like it would be helpful to have an accel version of
> DEFINE_DRM_GEM_FOPS() which helps accel drivers to get this right
Yeah, I also thought about it. I'll add it.
thanks,
oded
>
> > + * It looks up the correct ACCEL device and instantiates all the per-file
> > + * resources for it. It also calls the &drm_driver.open driver callback.
> > + *
> > + * Return: 0 on success or negative errno value on failure.
> > + */
> > +int accel_open(struct inode *inode, struct file *filp)
> > +{
> > +     struct drm_device *dev;
> > +     struct drm_minor *minor;
> > +     int retcode;
> > +
> > +     minor = accel_minor_acquire(iminor(inode));
> > +     if (IS_ERR(minor))
> > +             return PTR_ERR(minor);
> > +
> > +     dev = minor->dev;
> > +
> > +     atomic_fetch_inc(&dev->open_count);
> > +
> > +     /* share address_space across all char-devs of a single device */
> > +     filp->f_mapping = dev->anon_inode->i_mapping;
> > +
> > +     retcode = drm_open_helper(filp, minor);
> > +     if (retcode)
> > +             goto err_undo;
> > +
> > +     return 0;
> > +
> > +err_undo:
> > +     atomic_dec(&dev->open_count);
> > +     accel_minor_release(minor);
> > +     return retcode;
> > +}
> > +EXPORT_SYMBOL_GPL(accel_open);