Re: [RESEND PATCH 1/2] pinctrl: change function behavior for per pin muxing controllers
From: Stephen Warren
Date: Wed Jun 17 2015 - 11:55:38 EST
On 06/17/2015 06:38 AM, Ludovic Desroches wrote:
Hi Stephen,
On Mon, Jun 15, 2015 at 09:58:05AM -0600, Stephen Warren wrote:
On 06/10/2015 09:04 AM, Ludovic Desroches wrote:
When having a controller which allows per pin muxing, declaring with
which groups a function can be used is a useless constraint since groups
are something virtual.
This isn't true.
Irrespective of whether a particular piece of pinmux HW can control the mux
function for each pin individually, or only in groups, it's quite likely
that each function can only be selected onto a subset of those pins or
groups. Requiring the pinctrl driver to inform the core which set of
pins/groups particular functions can be selected onto seems quite
reasonable.
In my opinion at least, for HW that can select the mux function at the
per-pin level, the only sensible set of groups is one group per pin with
each group containing a single pin. Any other use of groups is a
SW/user-level construct, and is something unrelated to why the pinctrl
subsystem supports groups. If we want to represent those groups in pinctrl,
there should be two separate sets of groups; one to represent the actual HW
capabilities, and one to represent the SW/user-level convenience
abstractions.
Groups that I would like to use are not something related to the user or
software. It's an hardware reality but they would be more flexibles.
Usually the muxing is done by selecting a function (which seems to be
device related: usart, spi, etc.), then you select on which pins you
want this function.
In my case, I can't select a function only by choosing a mux. It is a
combination of the mux and the pin on which it is applied. So my
functions will be GPIO, A, B, C, etc. If I use function A on pin 12, I
will have my i2c clock signal but I can have this signal on pin 58 if I
use function C. Do you understand what I mean? It's not very easy to
explain... So here is a real example:
--------------------------------------------------
| | pio peripheral |
--------------------------------------------------
| signal | dir | func | signal | dir | ioset |
--------------------------------------------------
| PA8 | I/O | A | SDMMC0_DAT6 | I/O | 1 |
| | | B | QSPI1_IO1 | I/O | 1 |
| | | D | TCLK5 | I | 1 |
| | | E | FLEXCOM2_IO2 | I/O | 1 |
| | | F | NWE/NANDWE | O | 2 |
--------------------------------------------------
| PD28 | I/O | A | SPI1_NPCS0 | I/O | 3 |
| | | B | TDI | I/O | 3 |
| | | C | FLEXCOM2_IO2 | I | 2 |
--------------------------------------------------
You are right that having a group per pin is a solution.
If I follow your proposal (tell me if I'm wrong):
- I will have 128 groups since I have 128 pins.
Yes.
- I will have functions GPIO, A, B, C, D, E, F.
You could have functions A..F, and require the user to determine what
option they want for each pin, find the pin-specific mux function value
for each pin, and put that into the DT (or other pinmux data source).
For example, the bcm2835 pinctrl driver works this way.
In that case, each of the functions A..F could be selected on each pin,
so you'd have a very simple "get pins for function" implementation.
Alternatively, you could define a logic function per IO controller or
signal that gets pinmuxed. In the example above, FLEXCOM2_IO2 is one
such example. Given that set of functions, you'd need a mapping table to
convert from the logical functions seen by the pinctrl subsystem to the
HW values that need to be written into registers. For example, the Tegra
pinctrl drivers work this way.
In that case, each (pinctrl) function could only be selected on a
specific subset of all pins/groups, and so you'd probably need a
table-based implementation of "get pins for function".
- I have to give the groups which can achieve a function so I will have
128 groups for each function. It means 128 x 7 = 896 groups.
I don't think so no. I'm not sure why you'd consider multiplying 128 and
7 here. I'd expect 128 groups since you have 128 pins[1].
Well, it's possible to have slightly more groups if, say, mux function
is selectable per pin, whereas something else like drive strength is
configured by a register that affects multiple pins at once. You'd need
separate sets of groups for muxing and for drive strength configuration.
Some Tegra SoCs are like this. Still, we just add the different sets of
groups together here, not multiply. The overall set of groups is not
that much larger than the set of pins.
Does it seems to be something reasonable and intelligible? From my point
of view no. And what about the sysfs readability?
With my current implementation, I have something quite understandable
for the user if he needs to check the pinmuxing:
# cat /sys/kernel/debug/pinctrl/ahb\:apb\:pinctrl@fc038000/pinmux-pins
pin 17 (PA17): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 18 (PA18): b0000000.sdio-host (GPIO UNCLAIMED) function E group sdmmc1_0
pin 19 (PA19): b0000000.sdio-host (GPIO UNCLAIMED) function E group sdmmc1_0
# cat /sys/kernel/debug/pinctrl/pinctrl-maps
Pinctrl maps:
device b0000000.sdio-host
state default
type MUX_GROUP (2)
controlling device ahb:apb:pinctrl@fc038000
group sdmmc1_0
function E
device b0000000.sdio-host
state default
type CONFIGS_PIN (3)
controlling device ahb:apb:pinctrl@fc038000
pin PA28
config 00010003
device b0000000.sdio-host
state default
type CONFIGS_PIN (3)
controlling device ahb:apb:pinctrl@fc038000
pin PA18
config 00010003
Doing as you propose, I assume the result should be:
# cat /sys/kernel/debug/pinctrl/ahb\:apb\:pinctrl@fc038000/pinmux-pins
pin 17 (PA17): (MUX UNCLAIMED) (GPIO UNCLAIMED)
pin 18 (PA18): b0000000.sdio-host (GPIO UNCLAIMED) function E group PA18
pin 19 (PA19): b0000000.sdio-host (GPIO UNCLAIMED) function E group PA19
# cat /sys/kernel/debug/pinctrl/pinctrl-maps
Pinctrl maps:
device b0000000.sdio-host
state default
type MUX_GROUP (2)
controlling device ahb:apb:pinctrl@fc038000
group PA28
function E
device b0000000.sdio-host
state default
type CONFIGS_PIN (3)
controlling device ahb:apb:pinctrl@fc038000
pin PA28
config 00010003
device b0000000.sdio-host
state default
type MUX_GROUP (2)
controlling device ahb:apb:pinctrl@fc038000
group PA18
function E
device b0000000.sdio-host
state default
type CONFIGS_PIN (3)
controlling device ahb:apb:pinctrl@fc038000
pin PA18
config 00010003
I think it is more difficult to understand what is done here.
I don't think I agree. The HW level groups are the individual pins, so I
think the second option is clearer and more correct. What is the
"sdmmc1_0" group in the first example? Does any such thing even exist in HW?
I have sent patches months ago trying to improve things by having
something more flexible. I don't think I introduce too big changes.
The only answers I got were from people thinking that pinctrl framework
conception is not good to fit all kind of controllers. I re-sent the
patch series to gain more expose and have no answer...
I don't see anything in your description which implies pinctrl isn't
perfectly suitable for your HW.
Note that I'm on vacation for a couple weeks soon, and I don't expect to
follow this conversation during that time. Ultimately, LinusW owns the
pinctrl subsystem, and you need to convince him of any changes.
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