RE: [EXT] Re: [v3,2/2] i2c: mux: pca954x: support property idle-state

[Biwen Li]

> On 2019-10-16 06:09, Biwen Li wrote:
> > This supports property idle-state
> >
> > Signed-off-by: Biwen Li <biwen.li@xxxxxxx>
> > ---
> > Change in v3:
> >       - update subject and description
> >       - add a helper function pca954x_calculate_chan()
> >
> > Change in v2:
> >       - update subject and description
> >       - add property idle-state
> >
> >  drivers/i2c/muxes/i2c-mux-pca954x.c | 64
> > ++++++++++++++++++-----------
> >  1 file changed, 39 insertions(+), 25 deletions(-)
> >
> > diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c
> > b/drivers/i2c/muxes/i2c-mux-pca954x.c
> > index 923aa3a5a3dc..8777d429269c 100644
> > --- a/drivers/i2c/muxes/i2c-mux-pca954x.c
> > +++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
> > @@ -86,7 +86,7 @@ struct pca954x {
> >
> >       u8 last_chan;           /* last register value */
> >       /* MUX_IDLE_AS_IS, MUX_IDLE_DISCONNECT or >= 0 for channel */
> > -     s8 idle_state;
> > +     s32 idle_state;
> >
> >       struct i2c_client *client;
> >
> > @@ -229,22 +229,25 @@ static int pca954x_reg_write(struct i2c_adapter
> *adap,
> >                               I2C_SMBUS_BYTE, &dummy);  }
> >
> > +static int pca954x_calculate_chan(struct pca954x *data, u32 chan)
> 
> Should return u8, and "chan" is not what is calculated. Perhaps name the
> function pca954x_regval?
Okay, got it, I will change it in v4.
> 
> (Yes, last_chan is also clearly a bad name, and I suspect you may have
> based this name on it, but changing that is a separate patch.)
> 
> > +{
> > +     /* we make switches look like muxes, not sure how to be smarter */
> > +     if (data->chip->muxtype == pca954x_ismux)
> > +             return chan | data->chip->enable;
> > +     else
> > +             return 1 << chan;
> > +}
> > +
> >  static int pca954x_select_chan(struct i2c_mux_core *muxc, u32 chan)
> > {
> >       struct pca954x *data = i2c_mux_priv(muxc);
> >       struct i2c_client *client = data->client;
> > -     const struct chip_desc *chip = data->chip;
> >       u8 regval;
> >       int ret = 0;
> >
> > -     /* we make switches look like muxes, not sure how to be smarter */
> > -     if (chip->muxtype == pca954x_ismux)
> > -             regval = chan | chip->enable;
> > -     else
> > -             regval = 1 << chan;
> > -
> > +     regval = pca954x_calculate_chan(data, chan);
> 
> I think I would have kept the empty line here. Not important...
> 
> >       /* Only select the channel if its different from the last channel */
> > -     if (data->last_chan != regval) {
> > +     if ((data->last_chan & 0xff) != regval) {
> 
> The changes on this line are not needed (last_chan and regval are both u8)
> and just clutters up the code.
Okay, got it, I will not change it in v4.
> 
> >               ret = pca954x_reg_write(muxc->parent, client, regval);
> >               data->last_chan = ret < 0 ? 0 : regval;
> >       }
> > @@ -256,7 +259,7 @@ static int pca954x_deselect_mux(struct
> > i2c_mux_core *muxc, u32 chan)  {
> >       struct pca954x *data = i2c_mux_priv(muxc);
> >       struct i2c_client *client = data->client;
> > -     s8 idle_state;
> > +     s32 idle_state;
> >
> >       idle_state = READ_ONCE(data->idle_state);
> >       if (idle_state >= 0)
> > @@ -402,6 +405,23 @@ static void pca954x_cleanup(struct
> i2c_mux_core *muxc)
> >       i2c_mux_del_adapters(muxc);
> >  }
> >
> > +static int pca954x_init(struct i2c_client *client, struct pca954x
> > +*data) {
> > +     /*
> > +      * Write the mux register at addr to verify
> > +      * that the mux is in fact present. This also
> > +      * initializes the mux to a channel
> > +      * or disconnected state.
> > +      */
> 
> Again, this comment belongs in pca954x_probe before the call to this
> function.
> It does not apply (at least not the first sentence) when pca954x_init is called
> from pca954x_resume.
Okay, got it, thanks, I will move it in v4.
> 
> Hmmm, it could be argued that specifying MUX_IDLE_AS_IS should not
> trigger a disconnect on init (since the mux is always idle at init) and that
> some other method should be used to determine if the chip is present. The
> difference is that with the idle-state property you can explicitly request
> MUX_IDLE_AS_IS, while the old code only had some default behavior if
> i2c-mux-idle-disconnect was not present.
> 
> The easy way out of this is to, in the binding, document the situation and say
> that "idle-state = <MUX_IDLE_AS_IS>;" is not supported but that similar
> functionality can be obtained by leaving out both the
> i2c-mux-idle-disconnect and idle-state properties.
I will support MUX_IDLE_AS_IS in v4.

> 
> > +     if (data->idle_state >= 0) {
> > +             data->last_chan = pca954x_calculate_chan(data,
> data->idle_state);
> > +     } else {
> > +             /* Disconnect multiplexer */
> > +             data->last_chan = 0;
> > +     }
> > +     return i2c_smbus_write_byte(client, data->last_chan); }
> > +
> >  /*
> >   * I2C init/probing/exit functions
> >   */
> > @@ -411,7 +431,6 @@ static int pca954x_probe(struct i2c_client *client,
> >       struct i2c_adapter *adap = client->adapter;
> >       struct device *dev = &client->dev;
> >       struct device_node *np = dev->of_node;
> > -     bool idle_disconnect_dt;
> >       struct gpio_desc *gpio;
> >       struct i2c_mux_core *muxc;
> >       struct pca954x *data;
> > @@ -462,22 +481,18 @@ static int pca954x_probe(struct i2c_client
> *client,
> >               }
> >       }
> >
> > -     /* Write the mux register at addr to verify
> > -      * that the mux is in fact present. This also
> > -      * initializes the mux to disconnected state.
> > -      */
> > -     if (i2c_smbus_write_byte(client, 0) < 0) {
> > +     data->idle_state = MUX_IDLE_AS_IS;
> > +     if (np && of_property_read_u32(np, "idle-state", &data->idle_state))
> {
> > +             if (np && of_property_read_bool(np,
> > + "i2c-mux-idle-disconnect"))
> 
> You do not need to do the "np &&" part for both ifs, since it's already know
> that np is non-NULL when you hit the second if. But, it's a NOP in the first if,
> since of_property_read_u32 returns -EINVAL if it is. So, I suggest
> 
>         if (of_property_read_u32(np, "idle-state", &data->idle_state)) {
>                 if (np && of_property_read_bool(np,
> "i2c-mux-idle-disconnect"))
Okay, thanks, I will remove it in v4.
> 
> Cheers,
> Peter
> 
> > +                     data->idle_state = MUX_IDLE_DISCONNECT;
> > +     }
> > +
> > +     ret = pca954x_init(client, data);
> > +     if (ret < 0) {
> >               dev_warn(dev, "probe failed\n");
> >               return -ENODEV;
> >       }
> >
> > -     data->last_chan = 0;               /* force the first selection */
> > -     data->idle_state = MUX_IDLE_AS_IS;
> > -
> > -     idle_disconnect_dt = np &&
> > -             of_property_read_bool(np, "i2c-mux-idle-disconnect");
> > -     if (idle_disconnect_dt)
> > -             data->idle_state = MUX_IDLE_DISCONNECT;
> >
> >       ret = pca954x_irq_setup(muxc);
> >       if (ret)
> > @@ -531,8 +546,7 @@ static int pca954x_resume(struct device *dev)
> >       struct i2c_mux_core *muxc = i2c_get_clientdata(client);
> >       struct pca954x *data = i2c_mux_priv(muxc);
> >
> > -     data->last_chan = 0;
> > -     return i2c_smbus_write_byte(client, 0);
> > +     return pca954x_init(client, data);
> >  }
> >  #endif
> >
> >