pinctrl: Introduce TI IOdelay configuration driver

SoC family such as DRA7 family of processors have, in addition
to the regular muxing of pins (as done by pinctrl-single), a separate
hardware module called IODelay which is also expected to be configured.
The "IODelay" module has it's own register space that is independent
of the control module and the padconf register area.

With recent changes to the pinctrl framework, we can now support
this hardware with a reasonably minimal driver by using #pinctrl-cells,
GENERIC_PINCTRL_GROUPS and GENERIC_PINMUX_FUNCTIONS.

It is advocated strongly in TI's official documentation considering
the existing design of the DRA7 family of processors during mux or
IODelay reconfiguration, there is a potential for a significant glitch
which may cause functional impairment to certain hardware. It is
hence recommended to do as little of muxing as absolutely necessary
without I/O isolation (which can only be done in initial stages of
bootloader).

NOTE: with the system wide I/O isolation scheme present in DRA7 SoC
family, it is not reasonable to do stop all I/O operations for every
such pad configuration scheme. So, we will let it glitch when used in
this mode.

Even with the above limitation, certain functionality such as MMC has
mandatory need for IODelay reconfiguration requirements, depending on
speed of transfer. In these cases, with careful examination of usecase
involved, the expected glitch can be controlled such that it does not
impact functionality.

In short, IODelay module support as a padconf driver being introduced
here is not expected to do SoC wide I/O Isolation and is meant for
a limited subset of IODelay configuration requirements that need to
be dynamic and whose glitchy behavior will not cause functionality
failure for that interface.

IMPORTANT NOTE: we take the approach of keeping LOCK_BITs cleared
to 0x0 at all times, even when configuring Manual IO Timing Modes.
This is done by eliminating the LOCK_BIT=1 setting from Step
of the Manual IO timing Mode configuration procedure. This option
leaves the CFG_* registers unprotected from unintended writes to the
CTRL_CORE_PAD_* registers while Manual IO Timing Modes are configured.

This approach is taken to allow for a generic driver to exist in kernel
world that has to be used carefully in required usecases.

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
[tony@atomide.com: updated to use generic pinctrl functions, added
 binding documentation, updated comments]
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

1 files changed, 47 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/pinctrl/ti,iodelay.txt b/Documentation/devicetree/bindings/pinctrl/ti,iodelay.txt
new file mode 100644
index 000000000000..c3ed1232b6a3
--- /dev/null
+++ b/Documentation/devicetree/bindings/pinctrl/ti,iodelay.txt
@@ -0,0 +1,47 @@
+* Pin configuration for TI IODELAY controller
+
+TI dra7 based SoCs such as am57xx have a controller for setting the IO delay
+for each pin. For most part the IO delay values are programmed by the bootloader,
+but some pins need to be configured dynamically by the kernel such as the
+MMC pins.
+
+Required Properties:
+
+  - compatible: Must be "ti,dra7-iodelay"
+  - reg: Base address and length of the memory resource used
+  - #address-cells: Number of address cells
+  - #size-cells: Size of cells
+  - #pinctrl-cells: Number of pinctrl cells, must be 2. See also
+    Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
+
+Example
+-------
+
+In the SoC specific dtsi file:
+
+	dra7_iodelay_core: padconf@4844a000 {
+		compatible = "ti,dra7-iodelay";
+		reg = <0x4844a000 0x0d1c>;
+		#address-cells = <1>;
+		#size-cells = <0>;
+		#pinctrl-cells = <2>;
+	};
+
+In board-specific file:
+
+&dra7_iodelay_core {
+	mmc2_iodelay_3v3_conf: mmc2_iodelay_3v3_conf {
+		pinctrl-pin-array = <
+		0x18c A_DELAY_PS(0) G_DELAY_PS(120)	/* CFG_GPMC_A19_IN */
+		0x1a4 A_DELAY_PS(265) G_DELAY_PS(360)	/* CFG_GPMC_A20_IN */
+		0x1b0 A_DELAY_PS(0) G_DELAY_PS(120)	/* CFG_GPMC_A21_IN */
+		0x1bc A_DELAY_PS(0) G_DELAY_PS(120)	/* CFG_GPMC_A22_IN */
+		0x1c8 A_DELAY_PS(287) G_DELAY_PS(420)	/* CFG_GPMC_A23_IN */
+		0x1d4 A_DELAY_PS(144) G_DELAY_PS(240)	/* CFG_GPMC_A24_IN */
+		0x1e0 A_DELAY_PS(0) G_DELAY_PS(0)	/* CFG_GPMC_A25_IN */
+		0x1ec A_DELAY_PS(120) G_DELAY_PS(0)	/* CFG_GPMC_A26_IN */
+		0x1f8 A_DELAY_PS(120) G_DELAY_PS(180)	/* CFG_GPMC_A27_IN */
+		0x360 A_DELAY_PS(0) G_DELAY_PS(0)	/* CFG_GPMC_CS1_IN */
+		>;
+	};
+};