Re: [PATCH] Input: synaptics-rmi4 - switch to reduced reporting mode

[Christopher Heiny <Cheiny@synaptics.com>]

On Mon, 2020-01-27 at 11:21 -0800, Andrew Duggan wrote:
> Hi Dmitry,
> 
> On 1/26/20 6:24 PM, Dmitry Torokhov wrote:
> > 
> > On Mon, Jan 20, 2020 at 12:16:28PM +0100, Lucas Stach wrote:
> > > When the distance thresholds are set the controller must be in
> > > reduced
> > > reporting mode for them to have any effect on the interrupt
> > > generation.
> > > This has a potentially large impact on the number of events the
> > > host
> > > needs to process.
> > > 
> > > Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
> > > ---
> > > I'm not sure if we want a separate DT property to allow the use
> > > of
> > > reduced reporting mode, as this change might lead to problems for
> > > controllers with unreasonably large threshold values. I'm not
> > > sure if
> > > any controller with bogus threshold values exist in the wild.
> > > ---
> > Andrew, any feedback on this patch?
> > 
> > Thanks!
> 
> The RMI4 spec does say that delta X/Y thresholds are only used in 
> reduced reporting mode, so this patch is needed for the threshold
> values 
> to have an effect.
> 
> Reviewed-by: Andrew Duggan <aduggan@synaptics.com>
> 
> Because reduced reporting mode is so dependent on these thresholds,
> my 
> opinion is that it is better not to add a separate DT property, but
> to 
> instead control reduced reporting mode through the setting of these 
> thresholds. My guess is that the if reduced reporting is not enabled
> in 
> the firmware by default, then the thresholds may not be valid.
> Setting 
> the thresholds to 0 will essentially disable reduced reporting mode.
> So 
> that would be how a user could disable reduced reporting mode without
> a 
> separate DT property. Chris, do you have an opinion on this? Anything
> I 
> overlooked?

Hi Dmitry, Andrew, Lucas,

I'm in agreement with Andrew on this.  Having two ways to
enable/disable reduced reporting (that is, both the DT property and the
thresholds) could lead to confusion and unexpected behavior.  Simpler
is better, in my opinion.

However, in that case I'm a little concerned about the logic in the
patch below.  When either of the thresholds are set to non-zero, we
clear the report mask and then enable the reduced reporting bit. 
Subsequently setting both thresholds to zero will disable reduced
reporting, but will not enable another report mode.  Unless there is
code elsewhere to catch this case (and if there is, it seems like a bad
idea to be handling this in two different places), it could result in
the touchpad being disabled.

As a hypothetical instance of this, imagine a user using the touchpad
to manipulate report threshold sliders in a GUI.  Setting both sliders
to zero would disable the touch sensor reporting, potentially leaving
the user with a dead touch sensor and no easy way to recover from that.

					Cheers,
						Chris

> 
> Andrew
> 
> > >   drivers/input/rmi4/rmi_f11.c | 14 ++++++++++++++
> > >   1 file changed, 14 insertions(+)
> > > 
> > > diff --git a/drivers/input/rmi4/rmi_f11.c
> > > b/drivers/input/rmi4/rmi_f11.c
> > > index bbf9ae9f3f0c..6adea8a3e8fb 100644
> > > --- a/drivers/input/rmi4/rmi_f11.c
> > > +++ b/drivers/input/rmi4/rmi_f11.c
> > > @@ -412,6 +412,10 @@ struct f11_2d_sensor_queries {
> > > 
> > >   /* Defs for Ctrl0. */
> > >   #define RMI_F11_REPORT_MODE_MASK        0x07
> > > +#define RMI_F11_REPORT_MODE_CONTINUOUS  (0 << 0)
> > > +#define RMI_F11_REPORT_MODE_REDUCED     (1 << 0)
> > > +#define RMI_F11_REPORT_MODE_FS_CHANGE   (2 << 0)
> > > +#define RMI_F11_REPORT_MODE_FP_CHANGE   (3 << 0)
> > >   #define RMI_F11_ABS_POS_FILT            (1 << 3)
> > >   #define RMI_F11_REL_POS_FILT            (1 << 4)
> > >   #define RMI_F11_REL_BALLISTICS          (1 << 5)
> > > @@ -1195,6 +1199,16 @@ static int rmi_f11_initialize(struct
> > > rmi_function *fn)
> > >                ctrl->ctrl0_11[RMI_F11_DELTA_Y_THRESHOLD] =
> > >                        sensor->axis_align.delta_y_threshold;
> > > 
> > > +     /*
> > > +      * If distance threshold values are set, switch to reduced
> > > reporting
> > > +      * mode so they actually get used by the controller.
> > > +      */
> > > +     if (ctrl->ctrl0_11[RMI_F11_DELTA_X_THRESHOLD] ||
> > > +         ctrl->ctrl0_11[RMI_F11_DELTA_Y_THRESHOLD]) {
> > > +             ctrl->ctrl0_11[0] &= ~RMI_F11_REPORT_MODE_MASK;
> > > +             ctrl->ctrl0_11[0] |= RMI_F11_REPORT_MODE_REDUCED;
> > > +     }
> > > +
> > >        if (f11->sens_query.has_dribble) {
> > >                switch (sensor->dribble) {
> > >                case RMI_REG_STATE_OFF:
> > > --
> > > 2.20.1
> > > 
> > --
> > Dmitry