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Date: Mon, 25 Mar 2019 09:49:25 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Peter Rosin <peda@...ntia.se>
Cc: Pradeep Srinivasan <pradeeps@...ulusnetworks.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Rob Herring <robh+dt@...nel.org>,
Mark Rutland <mark.rutland@....com>,
"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
Ken Chen <chen.kenyy@...entec.com>
Subject: Re: [PATCH v2 5/5] i2c: mux: pca9541: add support for PCA9641
On Mon, Mar 25, 2019 at 03:01:21PM +0000, Peter Rosin wrote:
> On 2019-03-22 20:38, Pradeep Srinivasan wrote:
> > I have verified the changes on PCA 9541. May I know how you want the test results to be shared ? (newbie here; please bear with me)
> >
> > root@...ulus:/home/cumulus# dmesg| grep "pca9541" | grep -v "pmbus"
> > [ 2.922288] pca9541 1-0070: registered master selector for I2C pca9541
> >
> > root@...ulus:/home/cumulus# cat /sys/class/i2c-dev/i2c-1/device/1-0070/name
> > pca9541
>
> This only verifies that the probe works and that the chip is detected properly.
> It says nothing about if it works to communicate with whatever is beyond the
> PCA9541, and nothing on how the interaction with the "alien" other master
> connected to the PCA9541 is working. I don't know how I want this to be tested,
> but if you have a setup with a PCA9541 / PCA9641 I would assume that you
> have some kind of need for those chips and that you at least could report
> if basic xfers through them are working? I don't need to see actual commands
> that you have executed, I'm much more interested in some summary of what
> you did and what worked (or not).
>
> E.g. if you have an eeprom beyond the master selector, you could read from
> it in a loop while doing something else from the alien master and check if
> it all works as expected? Perhaps try to verify timing if there are stalls
> and/or timeouts etc. Go wild! But if you don't know how or don't have the
Something like that is what I did to test the original implementation: Access
all chips behind the mux from both ends continuously. Let that run for an hour
or so and declare it a success if there is no error. Usually, while the code
was still buggy, errors would show up within minutes, if not seconds.
Guenter
> time, I'd be happy with a report on basic functionality (but a little bit
> more than probe-ok would be nice though), because the code affecting the
> PCA9541 is probably not broken subtly, it either works as it did before or
> it doesn't work at all. And any problem with the PCA9641 side of things
> will not be a regression and therefore not a big problem...
>
> Cheers,
> Peter
>
> > I need to do the same on PCA 9641. If the above is sufficient, I will grab a switch with PCA 9641 and check if the driver works .
> >
> >
> > Thanks
> > Pradeep
> >
> > On Thu, Mar 7, 2019 at 1:16 PM Peter Rosin <peda@...ntia.se <mailto:peda@...ntia.se>> wrote:
> >
> > Hi!
> >
> > I should have read Kens code more carefully, before signing off on it...
> >
> > Review comments inline...
> >
> > On 2019-03-07 00:15, Peter Rosin wrote:
> > > Heavily based on code from Ken Chen <chen.kenyy@...entec.com <mailto:chen.kenyy@...entec.com>>.
> > >
> > > Signed-off-by: Peter Rosin <peda@...ntia.se <mailto:peda@...ntia.se>>
> > > ---
> > > drivers/i2c/muxes/Kconfig | 6 +-
> > > drivers/i2c/muxes/i2c-mux-pca9541.c | 137 ++++++++++++++++++++++++++++++++++--
> > > 2 files changed, 136 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/drivers/i2c/muxes/Kconfig b/drivers/i2c/muxes/Kconfig
> > > index 52a4a922e7e6..8532841de5db 100644
> > > --- a/drivers/i2c/muxes/Kconfig
> > > +++ b/drivers/i2c/muxes/Kconfig
> > > @@ -55,10 +55,10 @@ config I2C_MUX_LTC4306
> > > will be called i2c-mux-ltc4306.
> > >
> > > config I2C_MUX_PCA9541
> > > - tristate "NXP PCA9541 I2C Master Selector"
> > > + tristate "NXP PCA9541/PCA9641 I2C Master Selectors"
> > > help
> > > - If you say yes here you get support for the NXP PCA9541
> > > - I2C Master Selector.
> > > + If you say yes here you get support for the NXP PCA9541/PCA9641
> > > + I2C Master Selectors.
> > >
> > > This driver can also be built as a module. If so, the module
> > > will be called i2c-mux-pca9541.
> > > diff --git a/drivers/i2c/muxes/i2c-mux-pca9541.c b/drivers/i2c/muxes/i2c-mux-pca9541.c
> > > index 5eb36e3223d5..5d4e0c92e978 100644
> > > --- a/drivers/i2c/muxes/i2c-mux-pca9541.c
> > > +++ b/drivers/i2c/muxes/i2c-mux-pca9541.c
> > > @@ -1,5 +1,5 @@
> > > /*
> > > - * I2C multiplexer driver for PCA9541 bus master selector
> > > + * I2C multiplexer driver for PCA9541/PCA9641 bus master selectors
> > > *
> > > * Copyright (c) 2010 Ericsson AB.
> > > *
> > > @@ -28,8 +28,8 @@
> > > #include <linux/slab.h>
> > >
> > > /*
> > > - * The PCA9541 is a bus master selector. It supports two I2C masters connected
> > > - * to a single slave bus.
> > > + * The PCA9541 and PCA9641 are bus master selector. They support two I2C masters
> > > + * connected to a single slave bus.
> > > *
> > > * Before each bus transaction, a master has to acquire bus ownership. After the
> > > * transaction is complete, bus ownership has to be released. This fits well
> > > @@ -63,6 +63,33 @@
> > > #define PCA9541_BUSON (PCA9541_CTL_BUSON | PCA9541_CTL_NBUSON)
> > > #define PCA9541_MYBUS (PCA9541_CTL_MYBUS | PCA9541_CTL_NMYBUS)
> > >
> > > +#define PCA9641_ID 0x00
> > > +#define PCA9641_ID_MAGIC 0x38
> > > +
> > > +#define PCA9641_CONTROL 0x01
> > > +#define PCA9641_STATUS 0x02
> > > +#define PCA9641_TIME 0x03
> > > +
> > > +#define PCA9641_CTL_LOCK_REQ BIT(0)
> > > +#define PCA9641_CTL_LOCK_GRANT BIT(1)
> > > +#define PCA9641_CTL_BUS_CONNECT BIT(2)
> > > +#define PCA9641_CTL_BUS_INIT BIT(3)
> > > +#define PCA9641_CTL_SMBUS_SWRST BIT(4)
> > > +#define PCA9641_CTL_IDLE_TIMER_DIS BIT(5)
> > > +#define PCA9641_CTL_SMBUS_DIS BIT(6)
> > > +#define PCA9641_CTL_PRIORITY BIT(7)
> > > +
> > > +#define PCA9641_STS_OTHER_LOCK BIT(0)
> > > +#define PCA9641_STS_BUS_INIT_FAIL BIT(1)
> > > +#define PCA9641_STS_BUS_HUNG BIT(2)
> > > +#define PCA9641_STS_MBOX_EMPTY BIT(3)
> > > +#define PCA9641_STS_MBOX_FULL BIT(4)
> > > +#define PCA9641_STS_TEST_INT BIT(5)
> > > +#define PCA9641_STS_SCL_IO BIT(6)
> > > +#define PCA9641_STS_SDA_IO BIT(7)
> > > +
> > > +#define PCA9641_RES_TIME 0x03
> >
> > This appears to be the same thing as PCA9641_TIME above. The
> > register is called PCA9641_RT in my data sheet.
> >
> > > +
> > > /* arbitration timeouts, in jiffies */
> > > #define ARB_TIMEOUT (HZ / 8) /* 125 ms until forcing bus ownership */
> > > #define ARB2_TIMEOUT (HZ / 4) /* 250 ms until acquisition failure */
> > > @@ -73,6 +100,7 @@
> > >
> > > enum chip_name {
> > > pca9541,
> > > + pca9641,
> > > };
> > >
> > > struct chip_desc {
> > > @@ -102,6 +130,21 @@ static bool pca9541_busoff(int ctl)
> > > return (ctl & PCA9541_BUSON) == PCA9541_BUSON;
> > > }
> > >
> > > +static bool pca9641_lock_grant(int ctl)
> > > +{
> > > + return !!(ctl & PCA9641_CTL_LOCK_GRANT);
> > > +}
> > > +
> > > +static bool pca9641_other_lock(int sts)
> > > +{
> > > + return !!(sts & PCA9641_STS_OTHER_LOCK);
> > > +}
> > > +
> > > +static bool pca9641_busoff(int ctl, int sts)
> > > +{
> > > + return !pca9641_lock_grant(ctl) && !pca9641_other_lock(sts);
> > > +}
> > > +
> > > /*
> > > * Write to chip register. Don't use i2c_transfer()/i2c_smbus_xfer()
> > > * as they will try to lock the adapter a second time.
> > > @@ -256,6 +299,86 @@ static int pca9541_arbitrate(struct i2c_client *client)
> > > return 0;
> > > }
> > >
> > > +/* Release bus. */
> > > +static void pca9641_release_bus(struct i2c_client *client)
> > > +{
> > > + pca9541_reg_write(client, PCA9641_CONTROL, 0);
> >
> > Should this release bus function really "clobber" the control bits
> > PCA9641_CTL_IDLE_TIMER_DIS, PCA9641_CTL_SMBUS_DIS, PCA9641_CTL_PRIORITY?
> > Yes yes, the driver never sets these bits so they are likely zero. But
> > the driver doesn't reset the chip either, so some bootstrap code might
> > have configured those bits...
> >
> > Also related to bus release, since the driver does not touch the
> > reserve time register, and then clears the above bits, the only way
> > to release the bus is if everything continues to work and the above
> > pca9641_release_bus is in fact happening. But if the kernel crashes
> > while hogging the bus, and fails to come up, then the other master
> > has no way of stealing the ownership. I really feel that the driver
> > should make use of the timers so that the arbiter releases the bus
> > automatically on catastrophic failure. But maybe I plain and simple
> > just misunderstand the datasheet?
> >
> > > +}
> > > +
> > > +/*
> > > + * Channel arbitration
> > > + *
> > > + * Return values:
> > > + * <0: error
> > > + * 0 : bus not acquired
> > > + * 1 : bus acquired
> > > + */
> > > +static int pca9641_arbitrate(struct i2c_client *client)
> > > +{
> > > + struct i2c_mux_core *muxc = i2c_get_clientdata(client);
> > > + struct pca9541 *data = i2c_mux_priv(muxc);
> > > + int reg_ctl, reg_sts;
> > > +
> > > + reg_ctl = pca9541_reg_read(client, PCA9641_CONTROL);
> > > + if (reg_ctl < 0)
> > > + return reg_ctl;
> > > + reg_sts = pca9541_reg_read(client, PCA9641_STATUS);
> > > +
> > > + if (pca9641_busoff(reg_ctl, reg_sts)) {
> > > + /*
> > > + * Bus is off. Request ownership or turn it on unless
> > > + * other master requested ownership.
> > > + */
> > > + reg_ctl |= PCA9641_CTL_LOCK_REQ;
> > > + pca9541_reg_write(client, PCA9641_CONTROL, reg_ctl);
> > > + reg_ctl = pca9541_reg_read(client, PCA9641_CONTROL);
> > > +
> > > + if (pca9641_lock_grant(reg_ctl)) {
> > > + /*
> > > + * Other master did not request ownership,
> > > + * or arbitration timeout expired. Take the bus.
> > > + */
> > > + reg_ctl |= PCA9641_CTL_BUS_CONNECT |
> > > + PCA9641_CTL_LOCK_REQ;
> > > + pca9541_reg_write(client, PCA9641_CONTROL, reg_ctl);
> > > + data->select_timeout = SELECT_DELAY_SHORT;
> > > +
> > > + return 1;
> > > + }
> > > +
> > > + /*
> > > + * Other master requested ownership.
> > > + * Set extra long timeout to give it time to acquire it.
> > > + */
> > > + data->select_timeout = SELECT_DELAY_LONG * 2;
> > > +
> > > + return 0;
> > > + }
> > > +
> > > + if (pca9641_lock_grant(reg_ctl)) {
> > > + /*
> > > + * Bus is on, and we own it. We are done with acquisition.
> > > + */
> > > + reg_ctl |= PCA9641_CTL_BUS_CONNECT | PCA9641_CTL_LOCK_REQ;
> > > + pca9541_reg_write(client, PCA9641_CONTROL, reg_ctl);
> > > +
> > > + return 1;
> > > + }
> > > +
> > > + if (pca9641_other_lock(reg_sts)) {
> > > + /*
> > > + * Other master owns the bus.
> > > + * If arbitration timeout has expired, force ownership.
> > > + * Otherwise request it.
> >
> > This comment is stale. Reading the data sheet, I find no way to force
> > ownership with the PCA9641 (as indicated above in the release_bus
> > review comment). But I have only browsed the data sheet so I could
> > easily be mistaken...
> >
> > [time passes]
> >
> > Ahhh, wait, it could reset the chip to get a new chance to get ownership.
> > But that will reset all registers for the other master as well, since I
> > read it as if the reset is chip-global and not master-local with minimal
> > effects on the other master. So, a big hammer indeed.
> >
> > Cheers,
> > Peter
> >
> > > + */
> > > + data->select_timeout = SELECT_DELAY_LONG;
> > > + reg_ctl |= PCA9641_CTL_LOCK_REQ;
> > > + pca9541_reg_write(client, PCA9641_CONTROL, reg_ctl);
> > > + }
> > > +
> > > + return 0;
> > > +}
> > > +
> > > static int pca9541_select_chan(struct i2c_mux_core *muxc, u32 chan)
> > > {
> > > struct pca9541 *data = i2c_mux_priv(muxc);
> > > @@ -295,10 +418,15 @@ static const struct chip_desc chips[] = {
> > > .arbitrate = pca9541_arbitrate,
> > > .release_bus = pca9541_release_bus,
> > > },
> > > + [pca9641] = {
> > > + .arbitrate = pca9641_arbitrate,
> > > + .release_bus = pca9641_release_bus,
> > > + },
> > > };
> > >
> > > static const struct i2c_device_id pca9541_id[] = {
> > > { "pca9541", pca9541 },
> > > + { "pca9641", pca9641 },
> > > {}
> > > };
> > >
> > > @@ -307,6 +435,7 @@ MODULE_DEVICE_TABLE(i2c, pca9541_id);
> > > #ifdef CONFIG_OF
> > > static const struct of_device_id pca9541_of_match[] = {
> > > { .compatible = "nxp,pca9541", .data = &chips[pca9541] },
> > > + { .compatible = "nxp,pca9641", .data = &chips[pca9641] },
> > > {}
> > > };
> > > MODULE_DEVICE_TABLE(of, pca9541_of_match);
> > > @@ -392,5 +521,5 @@ static struct i2c_driver pca9541_driver = {
> > > module_i2c_driver(pca9541_driver);
> > >
> > > MODULE_AUTHOR("Guenter Roeck <linux@...ck-us.net <mailto:linux@...ck-us.net>>");
> > > -MODULE_DESCRIPTION("PCA9541 I2C master selector driver");
> > > +MODULE_DESCRIPTION("PCA9541/PCA9641 I2C master selector driver");
> > > MODULE_LICENSE("GPL v2");
> > >
> >
>
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