RE: [EXT] Re: [v5,2/3] i2c: mux: pca954x: support property idle-state

[Biwen Li]

> Hi!
> 
> I had a second read of this patch, and found a new issue.
> 
> On 2019-10-22 06:11, Biwen Li wrote:
> > This supports property idle-state,if present, overrides
> > i2c-mux-idle-disconnect.
> >
> > My use cases:
> >       - Use the property idle-state to fix
> >         an errata on LS2085ARDB and LS2088ARDB.
> >       - Errata id: E-00013(board LS2085ARDB and
> >         LS2088ARDB revision on Rev.B, Rev.C and Rev.D).
> >       - About E-00013:
> >         - Description: I2C1 and I2C3 buses
> >           are missing pull-up.
> >         - Impact: When the PCA954x device is tri-stated, the I2C bus
> >           will float. This makes the I2C bus and its associated
> >           downstream devices inaccessible.
> >         - Hardware fix: Populate resistors R189 and R190 for I2C1
> >           and resistors R228 and R229 for I2C3.
> >         - Software fix: Remove the tri-state option from the PCA954x
> >           driver(PCA954x always on enable status, specify a
> >           channel zero in dts to fix the errata E-00013).
> >
> > Signed-off-by: Biwen Li <biwen.li@xxxxxxx>
> > ---
> > Change in v5:
> >       - add extra precaution for pca954x_init
> >
> > Change in v4:
> >       - rename function
> >         pca954x_calculate_chan -> pca954x_regval
> >
> > 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 | 67
> > +++++++++++++++++++----------
> >  1 file changed, 44 insertions(+), 23 deletions(-)
> >
> > diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c
> > b/drivers/i2c/muxes/i2c-mux-pca954x.c
> > index 923aa3a5a3dc..218ba1a5ed7e 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;
> >
> > @@ -229,20 +229,23 @@ static int pca954x_reg_write(struct i2c_adapter
> *adap,
> >                               I2C_SMBUS_BYTE, &dummy);  }
> >
> > +static u8 pca954x_regval(struct pca954x *data, u8 chan) {
> > +     /* 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_regval(data, chan);
> >       /* Only select the channel if its different from the last channel */
> >       if (data->last_chan != regval) {
> >               ret = pca954x_reg_write(muxc->parent, client, 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 +405,25 @@ 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) {
> > +     int ret;
> > +     if (data->idle_state >= 0) {
> > +             data->last_chan = pca954x_regval(data, data->idle_state);
> > +     } else {
> > +             /* Disconnect multiplexer */
> > +             data->last_chan = 0;
> > +     }
> > +     ret = i2c_smbus_write_byte(client, data->last_chan);
> > +     if (ret < 0) {
> > +             data->last_chan = 0;
> > +             dev_err(&client->dev, "failed to verify the mux, \
> > +                     the mux maybe not present in fact\n");
> 
> This dev_err will trigger on probe failure, which already prints a message on
> failure. If you think you need a message if this fails in resume, I think that
> message needs to be printed in resume instead of here. But the message seems
> targeted at the probe failure, which is an argument for simply removing it. It is
> also not desirable to split a string with that technique. It's generally better to
> "use this technique to do string continuation on a new"
> "line." However, splitting strings over multiple lines are frowned upon since it
> breaks grepping for the error message. The language is also a bit strange.
> 
> Again, sorry for not being able to be as responsive as I would have liked, and
> thanks for your patience!
Okay, got it, thanks, I will adjust it in v6.
Best Regards,
Biwen Li
> 
> Cheers,
> Peter
> 
> > +     }
> > +
> > +     return ret;
> > +}
> > +
> >  /*
> >   * I2C init/probing/exit functions
> >   */
> > @@ -411,7 +433,6 @@ 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;
> > @@ -462,23 +483,24 @@ static int pca954x_probe(struct i2c_client *client,
> >               }
> >       }
> >
> > -     /* Write the mux register at addr to verify
> > +     data->idle_state = MUX_IDLE_AS_IS;
> > +     if (of_property_read_u32(np, "idle-state", &data->idle_state)) {
> > +             if (np && of_property_read_bool(np,
> "i2c-mux-idle-disconnect"))
> > +                     data->idle_state = MUX_IDLE_DISCONNECT;
> > +     }
> > +
> > +     /*
> > +      * Write the mux register at addr to verify
> >        * that the mux is in fact present. This also
> > -      * initializes the mux to disconnected state.
> > +      * initializes the mux to a channel
> > +      * or disconnected state.
> >        */
> > -     if (i2c_smbus_write_byte(client, 0) < 0) {
> > +     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)
> >               goto fail_cleanup;
> > @@ -531,8 +553,7 @@ 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
> >
> >