Re: [PATCH v2 1/5] of: Add descriptions of thermtrip properties to Tegra PMC bindings
From: Stephen Warren
Date: Fri Sep 05 2014 - 14:48:50 EST
On 09/05/2014 03:50 AM, Mikko Perttunen wrote:
Hi again!
I have fixed all other issues mentioned apart from this one. I can see
three ways ahead:
1) Keep things as is. There is a slight possibility that in the future
we will have a hardware configuration with multiple bus addresses and
this will cause annoyance.
2) Keep things otherwise as is, but read the bus address from the
thermtrip node. While at it, just have a reference to the the I2C bus
rather than the PMIC in the bindings.
3) Create a new poweroff driver class with two operations: poweroff and
get_i2c_command. The AS3722 poweroff "driver" is already separated from
the MFD and would be relatively straightforward to port to a new driver
subsystem. However, other PMICs we have, such as Palmas, don't do this
and would require larger refactoring. TBH, this smells of
overengineering to me.
4) Other ideas?
I think the two possible solutions are:
1) Put the following in the thermal node:
* phandle to I2C bus
* I2C address to write to (together with 7- or 10-bit indicator, if the
HW supports that)
* Device register address to write to (together with byte count
indicator if the HW supports that)
* Device register value (together with byte count indicator if the HW
supports that)
This seems simplest; it's a very direct representation of the HW, and
requires not extra infra-structure to be written or maintained. The only
issue is that it encodes register values in the DT which has previously
been frowned upon, and the values duplicate a tiny tiny part of the PMIC
driver. Personally, I don't think that's a big deal though.
or:
2) Put the following in the thermal node:
* phandle to I2C device of PMIC
... and have the thermal node's driver call function(s) in the PMIC
driver to retrieve all the information I mentioned above.
Any other option has too many holes or special cases that aren't covered.
What is your opinion?
Cheers,
Mikko
On 08/21/2014 08:54 PM, Stephen Warren wrote:
On 08/21/2014 10:53 AM, Thierry Reding wrote:
On Thu, Aug 21, 2014 at 09:38:29AM -0600, Stephen Warren wrote:
On 08/21/2014 12:58 AM, Thierry Reding wrote:
On Wed, Aug 20, 2014 at 02:16:49PM -0600, Stephen Warren wrote:
On 08/13/2014 06:41 AM, Mikko Perttunen wrote:
Hardware-triggered thermal reset requires configuring the I2C
reset procedure. This configuration is read from the device tree,
so document the relevant properties in the binding documentation.
diff --git
a/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-pmc.txt
b/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra20-pmc.txt
+- nvidia,pmu : Phandle to power management unit / PMIC handling
poweroff
+- nvidia,reg-addr : I2C register address to write poweroff
command to
+- nvidia,reg-data : Poweroff command to write to PMU
Why are both the PMU/PMIC phandle and the register address/data
required? I
thought the purpose of having the phandle was to allow the register
address
and data to be queried from the PMU/PMIC driver.
To me, it seems much simpler to get rid of the phandle and just
hard-code
the I2C bus number, address, and data into this node, rather than
having to
go query it from the PMU/PMIC driver, then find the I2C controller,
then
query it for its ID (and hope that all HW modules that talk to I2C
controllers directly use the same numbering scheme...)
I originally requested this to be changed. It seems wrong to duplicate
information about the PMIC in both the PMIC device tree node and the
i2c-thermtrip node if we can get the same information from the driver
directly (via the phandle). It certainly requires a little more code,
but at the advantage of not having to figure out the I2C controller
hardware number and I2C slave addresses when writing the i2c-thermtrip
node.
I cant see that argument, but surely the PMIC driver can also supply
the
Oops, that was meant to be can not cant.
"reg-addr" and "reg-data" values too, if it's already being queried
for the
I2C device address and bus number? The binding above appears to
duplicate
part of the information, while requiring querying of the other part.
I suppose that could be done. It would take a new function to do that,
though, since I'm not aware of a generic mechanism to query this kind of
information from a PMIC (there's no generic PMIC API, either, so perhaps
it would be a good time to create one?). The I2C controller and I2C
slave are generic I2C properties, whereas the register and data to power
off the device are very device specific.
I don't think it's possible to generically query an I2C device for its
address from the struct i2c_device object; the code still needs to call
a function in the PMIC driver to obtain this.
That's because some I2C devices respond to multiple I2C addresses, and
there's no guarantee that the one I2C address in the DT (and hence the
struct i2c_device) is the address upon which the regulator function
exists.
grep for i2c_new_dummy in drivers/mfd and you'll find quite a few
examples. The Atmel MXT touchpad/screen is another example.
--
To unsubscribe from this list: send the line "unsubscribe linux-tegra" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-tegra" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/