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Date:   Thu, 3 Nov 2022 14:25:54 +0900
From:   Jiho Chu <jiho.chu@samsung.com>
To:     Oded Gabbay <ogabbay@kernel.org>
Cc:     David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
        Jason Gunthorpe <jgg@nvidia.com>,
        John Hubbard <jhubbard@nvidia.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Yuji Ishikawa <yuji2.ishikawa@toshiba.co.jp>,
        Daniel Stone <daniel@fooishbar.org>,
        Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
        Jeffrey Hugo <quic_jhugo@quicinc.com>,
        Christoph Hellwig <hch@infradead.org>,
        Kevin Hilman <khilman@baylibre.com>,
        Jagan Teki <jagan@amarulasolutions.com>,
        Jacek Lawrynowicz <jacek.lawrynowicz@linux.intel.com>,
        Maciej Kwapulinski <maciej.kwapulinski@linux.intel.com>
Subject: Re: [RFC PATCH v2 2/3] accel: add dedicated minor for accelerator
 devices
Message-Id: <20221103142554.6310a60f0f6dad1a59fa7644@samsung.com>
In-Reply-To: <20221102203405.1797491-3-ogabbay@kernel.org>
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        <CGME20221102203430epcas1p380845d7a6ebc38ab1f41acf8c48a4480@epcas1p3.samsung.com>
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On Wed,  2 Nov 2022 22:34:04 +0200
Oded Gabbay <ogabbay@kernel.org> wrote:

> +/**
> + * 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.
> + * 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);
> +

Hi,
It needs to consider drm_global_mutex to access open_count.
please check doxy of 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);
> +
>  static int accel_stub_open(struct inode *inode, struct file *filp)
>  {
> -	DRM_DEBUG("Operation not supported");
> +	const struct file_operations *new_fops;
> +	struct drm_minor *minor;
> +	int err;
> +
> +	DRM_DEBUG("\n");

It seems useless.

Thanks.
Jiho Chu