Re: [PATCH v4 01/24] input: Add ff-memless-next module

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

Hi Michal,

On Sat, Apr 26, 2014 at 05:02:00PM +0200, Michal Malý wrote:
> +
> +/** DEFINITION OF TERMS
> + *
> + * Combined effect - An effect whose force is a superposition of forces
> + *                   generated by all effects that can be added together.
> + *                   Only one combined effect can be playing at a time.
> + *                   Effects that can be added together to create a combined
> + *                   effect are FF_CONSTANT, FF_PERIODIC and FF_RAMP.
> + * Uncombinable effect - An effect that cannot be combined with another effect.
> + *                       All conditional effects - FF_DAMPER, FF_FRICTION,
> + *                       FF_INERTIA and FF_SPRING are uncombinable.
> + *                       Number of uncombinable effects playing simultaneously
> + *                       depends on the capabilities of the hardware.
> + * Rumble effect - An effect generated by device's rumble motors instead of
> + *                 force feedback actuators.
> + *
> + *
> + * HANDLING OF UNCOMBINABLE EFFECTS
> + *
> + * Uncombinable effects cannot be combined together into just one effect, at
> + * least not in a clear and obvious manner. Therefore these effects have to
> + * be handled individually by ff-memless-next. Handling of these effects is
> + * left entirely to the hardware-specific driver, ff-memless-next merely
> + * passes these effects to the hardware-specific driver at appropriate time.
> + * ff-memless-next provides the UPLOAD command to notify the hardware-specific
> + * driver that the userspace is about to request playback of an uncombinable
> + * effect. The hardware-specific driver shall take all steps needed to make
> + * the device ready to play the effect when it receives the UPLOAD command.
> + * The actual playback shall commence when START_UNCOMB command is received.
> + * Opposite to the UPLOAD command is the ERASE command which tells
> + * the hardware-specific driver that the playback has finished and that
> + * the effect will not be restarted. STOP_UNCOMB command tells
> + * the hardware-specific driver that the playback shall stop but the device
> + * shall still be ready to resume the playback immediately.
> + *
> + * In case it is not possible to make the device ready to play an uncombinable
> + * effect (all hardware effect slots are occupied), the hardware-specific
> + * driver may return an error when it receives an UPLOAD command. If the

This part concerns me. It seems to me that devices supporting
"uncombinable" effects are in fact not memoryless devices and we should
not be introducing this term here. If the goal is to work around limited
number of effect slots in the devices by combining certain effects then
it needs to be done at ff-core level as it will be potentially useful
for all devices.

> + * hardware-specific driver returns 0, the upload is considered successful.
> + * START_UNCOMB and STOP_UNCOMB commands cannot fail and the device must always
> + * start the playback of the requested effect if the UPLOAD command of the
> + * respective effect has been successful. ff-memless-next will never send
> + * a START/STOP_UNCOMB command for an effect that has not been uploaded
> + * successfully, nor will it send an ERASE command for an effect that is
> + * playing (= has been started with START_UNCOMB command).

> + */
> +
> +enum mlnx_commands {
> +	/* Start or update a combined effect. This command is sent whenever
> +	 * a FF_CONSTANT, FF_PERIODIC or FF_RAMP is started, stopped or
> +	 * updated by userspace, when the applied envelopes are recalculated
> +	 * or when periodic effects are recalculated. */
> +	MLNX_START_COMBINED,
> +	/* Stop combined effect. This command is sent when all combinable
> +	 * effects are stopped. */
> +	MLNX_STOP_COMBINED,
> +	/* Start or update a rumble effect. This command is sent whenever
> +	 * a FF_RUMBLE effect is started or when its magnitudes or directions
> +	 * change. */
> +	MLNX_START_RUMBLE,
> +	/* Stop a rumble effect. This command is sent when all FF_RUMBLE
> +	 * effects are stopped. */
> +	MLNX_STOP_RUMBLE,
> +	/* Start or update an uncombinable effect. This command is sent
> +	 * whenever an uncombinable effect is started or updated. */

Why do we have make a distinction between rumble and all other effects?

-- 
Dmitry