linux-kernel - Re: [GIT PULL 5/9] intel_th: msu: Introduce buffer driver interface

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Message-ID: <87h883t6vd.fsf@ashishki-desk.ger.corp.intel.com>
Date:   Wed, 03 Jul 2019 19:33:58 +0300
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        alexander.shishkin@...ux.intel.com
Subject: Re: [GIT PULL 5/9] intel_th: msu: Introduce buffer driver interface

Greg Kroah-Hartman <gregkh@...uxfoundation.org> writes:

>> +	/*
>> +	 * ->assign() called when buffer 'mode' is set to this driver
>> +	 *   (aka mode_store())
>> +	 * @device:	struct device * of the msc
>> +	 * @mode:	allows the driver to set HW mode (see the enum above)
>> +	 * Returns:	a pointer to a private structure associated with this
>> +	 *		msc or NULL in case of error. This private structure
>> +	 *		will then be passed into all other callbacks.
>> +	 */
>> +	void	*(*assign)(struct device *dev, int *mode);
>> +	/* ->unassign():	some other mode is selected, clean up */
>> +	void	(*unassign)(void *priv);
>> +	/*
>> +	 * ->alloc_window(): allocate memory for the window of a given
>> +	 *		size
>> +	 * @sgt:	pointer to sg_table, can be overridden by the buffer
>> +	 *		driver, or kept intact
>> +	 * Returns:	number of sg table entries <= number of pages;
>> +	 *		0 is treated as an allocation failure.
>> +	 */
>> +	int	(*alloc_window)(void *priv, struct sg_table **sgt,
>> +				size_t size);
>> +	void	(*free_window)(void *priv, struct sg_table *sgt);
>> +	/* ->activate():	trace has started */
>> +	void	(*activate)(void *priv);
>> +	/* ->deactivate():	trace is about to stop */
>> +	void	(*deactivate)(void *priv);
>> +	/*
>> +	 * ->ready():	window @sgt is filled up to the last block OR
>> +	 *		tracing is stopped by the user; this window contains
>> +	 *		@bytes data. The window in question transitions into
>> +	 *		the "LOCKED" state, indicating that it can't be used
>> +	 *		by hardware. To clear this state and make the window
>> +	 *		available to the hardware again, call
>> +	 *		intel_th_msc_window_unlock().
>> +	 */
>> +	int	(*ready)(void *priv, struct sg_table *sgt, size_t bytes);
>> +};
>
> Why isn't this based off of 'struct driver'?

It's not a real driver, in a sense that there's no underlying
device. None of the usual driver stuff applies. It's still a set of
callbacks, though. Should this be an elaborate comment, should I replace
the word "driver" with something else?

I'd really like to avoid shoehorning the whole 'struct device' + 'struct
driver' here.

Thanks,
--
Alex