path: root/Documentation/pinctrl.txt
diff options
authorLinus Walleij <linus.walleij@linaro.org>2012-10-17 18:51:54 (GMT)
committerLinus Walleij <linus.walleij@linaro.org>2012-11-11 18:05:56 (GMT)
commit1a78958dc212f3698fdc543857af80155cb30f7f (patch)
tree4efd595b3cc9f6fe0fc97bfd6b53a25d1f5bded6 /Documentation/pinctrl.txt
parent77b67063bb6bce6d475e910d3b886a606d0d91f7 (diff)
pinctrl: reserve pins when states are activated
This switches the way that pins are reserved for multiplexing: We used to do this when the map was parsed, at the creation of the settings inside the pinctrl handle, in pinmux_map_to_setting(). However this does not work for us, because we want to use the same set of pins with different devices at different times: the current code assumes that the pin groups in a pinmux state will only be used with one single device, albeit different groups can be active at different times. For example if a single I2C driver block is used to drive two different busses located on two pin groups A and B, then the pins for all possible states of a function are reserved when fetching the pinctrl handle: the I2C bus can choose either set A or set B by a mux state at runtime, but all pins in both group A and B (the superset) are effectively reserved for that I2C function and mapped to the device. Another device can never get in and use the pins in group A, even if the device/function is using group B at the moment. Instead: let use reserve the pins when the state is activated and drop them when the state is disabled, i.e. when we move to another state. This way different devices/functions can use the same pins at different times. We know that this is an odd way of doing things, but we really need to switch e.g. an SD-card slot to become a tracing output sink at runtime: we plug in a special "tracing card" then mux the pins that used to be an SD slot around to the tracing unit and push out tracing data there instead of SD-card traffic. As a side effect pinmux_free_setting() is unused but the stubs are kept for future additions of code. Cc: Patrice Chotard <patrice.chotard@st.com> Cc: Loic Pallardy <loic.pallardy@st.com> Acked-by: Stephen Warren <swarren@nvidia.com> Tested-by: Jean Nicolas Graux <jean-nicolas.graux@stericsson.com> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Diffstat (limited to 'Documentation/pinctrl.txt')
1 files changed, 3 insertions, 1 deletions
diff --git a/Documentation/pinctrl.txt b/Documentation/pinctrl.txt
index 3b4ee53..a1cd2f9 100644
--- a/Documentation/pinctrl.txt
+++ b/Documentation/pinctrl.txt
@@ -1193,4 +1193,6 @@ foo_switch()
-The above has to be done from process context.
+The above has to be done from process context. The reservation of the pins
+will be done when the state is activated, so in effect one specific pin
+can be used by different functions at different times on a running system.

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