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Date: Mon, 30 Sep 2019 02:43:40 +0000
From: Biwen Li <biwen.li@....com>
To: Peter Rosin <peda@...ntia.se>, Leo Li <leoyang.li@....com>
CC: "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [EXT] Re: [PATCH] i2c: pca954x: Add property to skip disabling
PCA954x MUX device
>
> On 2019-09-29 12:36, Biwen Li wrote:
> > On some Layerscape boards like LS2085ARDB and LS2088ARDB, input
> > pull-up resistors on PCA954x MUX device are missing on board, So, if
> > MUX are disabled after powered-on, input lines will float leading to
> > incorrect functionality.
>
> Hi!
>
> Are you saying that the parent bus of the mux is relying on some pull-ups inside
> the mux?
Yes, as follows:
VCC
-------
|-------------------
| |
\ \
/10K resister / 10k resister
\ \
| |
| |
I2C1_SCL ------------------------ I2C1_SCL | ----------------------
--------------------|SCL | ----------------------------------------|SCL |
I2C1_SDA | PCA9547 | I2C1_SDA | | PCA9547 |
--------------------|SDA | ----------------------------|-----------|SDA |
------------------------ ----------------------
--wrong design(need software fix as above or hardware fix)-- --proper design--
>
> > Hence, PCA954x MUX device should never be turned-off after power-on.
> >
> > Add property to skip disabling PCA954x MUX device if device tree
> > contains "i2c-mux-never-disable"
> > for PCA954x device node.
> >
> > Errata ID: E-00013 on board LS2085ARDB and LS2088ARDB (Board revision
> > found on Rev.B, Rev.C and Rev.D)
>
> I think you should follow the example of the i2c-mux-gpio driver and implement
> the idle-state property instead.
>
> That is a lot more consistent, assuming it solves the problem at hand?
Got it, thanks, I will try it.
>
> >
> > Signed-off-by: Biwen Li <biwen.li@....com>
> > ---
> > drivers/i2c/muxes/i2c-mux-pca954x.c | 33
> > +++++++++++++++++++++++++----
> > 1 file changed, 29 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/i2c/muxes/i2c-mux-pca954x.c
> > b/drivers/i2c/muxes/i2c-mux-pca954x.c
> > index 923aa3a5a3dc..ea8aca54d572 100644
> > --- a/drivers/i2c/muxes/i2c-mux-pca954x.c
> > +++ b/drivers/i2c/muxes/i2c-mux-pca954x.c
> > @@ -93,6 +93,7 @@ struct pca954x {
> > struct irq_domain *irq;
> > unsigned int irq_mask;
> > raw_spinlock_t lock;
> > + u8 disable_mux; /* do not disable mux if val not 0 */
>
> Awful number of negations there. The name is also backwards given that a
> non-zero value means that the mux should *not* be disabled. I would have
> reused the name from the binding.
>
> bool never_disable;
>
> A bit less confusing...
Got it,thanks, I will let it clear in v2.
>
> > };
> >
> > /* Provide specs for the PCA954x types we know about */ @@ -258,6
> > +259,11 @@ static int pca954x_deselect_mux(struct i2c_mux_core *muxc,
> u32 chan)
> > struct i2c_client *client = data->client;
> > s8 idle_state;
> >
> > + if (data->disable_mux != 0) {
>
> Please drop " != 0" and use the variable as a truth value. More instances below...
Got it, I will correct it in v2.
>
> > + data->last_chan = data->chip->nchans;
> > + return pca954x_reg_write(muxc->parent, client,
> data->disable_mux);
> > + }
> > +
> > idle_state = READ_ONCE(data->idle_state);
> > if (idle_state >= 0)
> > /* Set the mux back to a predetermined channel */ @@
> > -462,16 +468,32 @@ static int pca954x_probe(struct i2c_client *client,
> > }
> > }
> >
> > + /* Errata ID E-00013 on board LS2088ARDB and LS2088ARDB:
> > + * The point here is that you must not disable a mux if there
> > + * are no pullups on the input or you mess up the I2C. This
> > + * needs to be put into the DTS really as the kernel cannot
> > + * know this otherwise.
> > + */
> > +
> > + data->disable_mux = np &&
> > + of_property_read_bool(np, "i2c-mux-never-disable") &&
>
> i2c-mux-never-disable needs to be documented. However see above for my
> point that you should do it like the i2c-mux-gpio driver. Any usage of idle-state
> still needs to be documented for pca954x binding.
Got it, I will update the document in v2.
>
> > + data->chip->muxtype == pca954x_ismux ?
> > + data->chip->enable : 0;
>
> Why do you not allow never-disable for switches?
Currently, the hardware bug is on pca9547(LS2085ARDB and LS2088ARDB not populate resistors for pca9547),
muxtype of pca9547 is 'pca954x_ismux'
>
> Cheers,
> Peter
>
> > +
> > /* 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) {
> > + if (i2c_smbus_write_byte(client, data->disable_mux) < 0) {
> > dev_warn(dev, "probe failed\n");
> > return -ENODEV;
> > }
> >
> > - data->last_chan = 0; /* force the first selection */
> > + if (data->disable_mux != 0)
> > + data->last_chan = data->chip->nchans;
> > + else
> > + data->last_chan = 0; /* force the first
> selection */
> > +
> > data->idle_state = MUX_IDLE_AS_IS;
> >
> > idle_disconnect_dt = np &&
> > @@ -531,8 +553,11 @@ 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);
> > + if (data->disable_mux != 0)
> > + data->last_chan = data->chip->nchans;
> > + else
> > + data->last_chan = 0;
> > + return i2c_smbus_write_byte(client, data->disable_mux);
> > }
> > #endif
> >
> >
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