On 08/26/2016 10:38 AM, Jon Hunter wrote:
On 26/08/16 16:55, Stephen Warren wrote:
On 08/26/2016 07:09 AM, Jon Hunter wrote:
On Tegra124/132 the pins for I2C6 are shared with the Display Port AUX
(DPAUX) channel and on Tegra210 the pins for I2C4 and I2C6 are shared
with DPAUX1 and DPAUX0, respectively. The multiplexing of the pins is
handled by a register in the DPAUX and so the Tegra DPAUX driver has
been updated to register a pinctrl device for managing these pins.
The pins for these particular I2C devices are bound to the I2C device
prior to probing. However, these I2C devices are in a different power
partition to the DPAUX devices that own the pins. Hence, it is desirable
to place the pins in the 'idle' state and allow the DPAUX power
partition to switch off, when these I2C devices is not in use.
Therefore, add calls to place the I2C pins in the 'default' and 'idle'
states when the I2C device is runtime resumed and suspended,
respectively.
Please note that the pinctrl functions that set the state of the pins
check to see if the devices has pins associated and will return zero
if they do not. Therefore, it is safe to call these pinctrl functions
even for I2C devices that do not have any pins associated.
I think this should be handled by drivers/i2c/muxes/i2c-mux-pinctrl.c
instead?
I remember having a look at i2c-mux some time back, but we did not have
requirement to share the pins dynamically at runtime between the DPAUX
and I2C devices.
The pins are just configured at probe time for either the DPAUX or I2C
device and then with this change when we are not active we can power
down the pins. However, the pins are always bound to either the DPAUX or
I2C.
Oh, so this isn't about 1 controller accessing 2 different physical
buses at runtime by re-routing the SoC pinmux (which is the use-case
i2c-mux-pinctrl handles), but simply about power-management.
If the I2C controller didn't need to set a different pinctrl state
during idle, I would say that all the pin muxing should be set up at
system boot time, just like every other part of the pinmux is. In that
case, the fact that the pins could be routed to 1 of 2 I2C controllers
(DPAUX0 vs. I2C4) is irrelevant to the patch; the routing is a static
thing anyway.
Thinking some more, i2c-mux-pinctrl actually could handle this case,
since it does define an idle pinmux state IIRC, or at least could be
trivially extended to do so. That said, doing this directly in the I2C
driver does seem better in this case, since the use-case is power about
the power advantages for a single bus, rather than anything to do with
multiple buses.
Hence I'm OK with the concept of this patch. I didn't review the code
though.
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