Date:	Thu, 26 Apr 2012 16:44:46 +0200
From:	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>
To:	Dong Aisheng <b29396@...escale.com>
Cc:	linux-kernel@...r.kernel.org, b20223@...escale.com,
	linus.walleij@...ricsson.com, devicetree-discuss@...ts.ozlabs.org,
	rob.herring@...xeda.com, linux-arm-kernel@...ts.infradead.org,
	kernel@...gutronix.de, cjb@...top.org, s.hauer@...gutronix.de
Subject: Re: [PATCH v3 2/4] pinctrl: pinctrl-imx: add imx pinctrl core
 driver

On 22:40 Thu 26 Apr     , Dong Aisheng wrote:
> From: Dong Aisheng <dong.aisheng@...aro.org>
> 
> The driver has mux and config support while the gpio is still
> not supported.
> For select input setting, the driver will handle it internally
> and do not need user to take care of it.
> 
> The pinctrl-imx core driver will parse the dts file and dynamically
> create the pinmux functions and groups.
> 
> Each IMX SoC pinctrl driver should register pins with a pin register map
> including mux register and config register and select input map to core
> for proper operations.
> 
> Signed-off-by: Dong Aisheng <dong.aisheng@...aro.org>
> 
> ---
> ChangeLog: v2->v3:
> * add missed SION bit set from device tree
>   Thanks for Richard Zhao's reminder.
> ChangeLog: v1->v2:
> * Change the binding a bit.
>   For fsl,pins property, change it from pin name strings to pin function id
>   which represents a pin working on a specific function. Then we can remove
>   fsl,mux property since the pin function id already contains the mux setting.
>   Also remove other pin config property in the first patch.
>   Because in the future, we will switch to use dtc macro, then using a lot of
>   propertys to represent the each pin config like pull, speed and etc seems
>   needless.
>   Then each pin entry in dts file becomes a pair of PIN_FUNC_ID and CONFIG:
>   fsl,pins = <PIN_FUNC_ID CONFIG ..>
>   See binding doc for details.
> * Sascha raised a question that pins in the same group may have different
>   pad setting for example I2C_CLK needs pull up while I2C_DAT not.
>   The v1 driver can aslo handle this issue but needs split the different
>   pad setting pins into different groups which loses a bit flexibility.
>   Also suggested by Richard Zhao and Jason Liu, we may still want the iomux
>   v3 simililar using way that allows each pin has the abiblity to configure
>   its pad which seems reasonable because from HW point of view, FSL IMX are
>   indeed pin based SoC which should be able to set per pin.
>   So the main changes in this v2 patch are change to support per pin config.
>   Then the using of iomux is almost the same as the existing iomux v3 for
>   non dt imx platforms. See binding doc for example.
> 
>   After introduce the new way, there're mainly two known issues:
>   1) Since many pins in the same group may have the same pad config setting,
>      thus there may be some data redundance, however, since it's one word
>      and it's purely describe hw i would think it's not a big issue.
>   2) Need a magic number to indicate no pad config need. In current iomux v3,
>      It's 1<<16 which is not used by IMX5, i used 1<<31 for both MX5 and MX6.
>      However, it's definitely possibile that in the future, the bit 31 may also
>      be used, that means we may need change the binding doc or just handle it in
>      driver for different SoCs.
>   3) Due to core limitation, the current pinconf_group_set/get only support
>      get/set the same config(a u32 value)for all the pins in the same group,
>      so i removed the imx_group_set/get functions support, instead, using
>      imx_pin_get/set.
>      About this limitation, we may need some futher discussion on if we may
>      need to enhance it to be more flexible to support configure different
>      pins in the same group.
> * Refactor probe handling based on Stephen's suggestion.
> * Enhanced the binding doc and split it into two part, pinctrl-imx common part
>   and pinctrl-soc driver part.
> * Change functions name from imx_pmx_* to imx_pinctrl_*.
> * Other fixes based on Sascha, Stephen, Linus, Shawn's comments.
> ---
>  .../bindings/pinctrl/fsl,imx-pinctrl.txt           |   93 +++
>  drivers/pinctrl/Kconfig                            |    5 +
>  drivers/pinctrl/Makefile                           |    1 +
>  drivers/pinctrl/pinctrl-imx.c                      |  627 ++++++++++++++++++++
>  drivers/pinctrl/pinctrl-imx.h                      |  106 ++++
>  5 files changed, 832 insertions(+), 0 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/pinctrl/fsl,imx-pinctrl.txt
>  create mode 100644 drivers/pinctrl/pinctrl-imx.c
>  create mode 100644 drivers/pinctrl/pinctrl-imx.h
> 
> diff --git a/Documentation/devicetree/bindings/pinctrl/fsl,imx-pinctrl.txt b/Documentation/devicetree/bindings/pinctrl/fsl,imx-pinctrl.txt
> new file mode 100644
> index 0000000..e00c7fc
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/pinctrl/fsl,imx-pinctrl.txt
> @@ -0,0 +1,93 @@
> +* Freescale IOMUX Controller (IOMUXC) for i.MX
> +
> +The IOMUX Controller (IOMUXC), together with the IOMUX, enables the IC
> +to share one PAD to several functional blocks. The sharing is done by
> +multiplexing the PAD input/output signals. For each PAD there are up to
> +8 muxing options (called ALT modes). Since different modules require
> +different PAD settings (like pull up, keeper, etc) the IOMUXC controls
> +also the PAD settings parameters.
> +
> +Please refer to pinctrl-bindings.txt in this directory for details of the
> +common pinctrl bindings used by client devices, including the meaning of the
> +phrase "pin configuration node".
> +
> +Freescale IMX pin configuration node is a node of a group of pins which can be
> +used for a specific device or function. This node represents both mux and config
> +of the pins in that group. The 'mux' selects the function mode(also named mux
> +mode) this pin can work on and the 'config' configures various pad settings
> +such as pull-up, open drain, drive strength, etc.
> +
> +Required properties for iomux controller:
> +- compatible: "fsl,<soc>-iomuxc"
> +  Please refer to each fsl,<soc>-pinctrl.txt binding doc for supported SoCs.
> +
> +Required properties for pin configuration node:
> +- fsl,pins: two integers array, represents a group of pins mux and config
> +  setting. The format is fsl,pins = <PIN_FUNC_ID CONFIG>, PIN_FUNC_ID is a
> +  pin working on a specific function, CONFIG is the pad setting value like
> +  pull-up on this pin. Please refer to fsl,<soc>-pinctrl.txt for the valid
> +  pins and functions of each SoC.
> +
> +Bits used for CONFIG:
> +NO_PAD_CTL(1 << 31): indicate this pin does not need config.
> +
> +SION(1 << 30): Software Input On Field.
> +Force the selected mux mode input path no matter of MUX_MODE functionality.
> +By default the input path is determined by functionality of the selected
> +mux mode (regular).
> +
> +Other bits are used for PAD setting.
> +
> +NOTE:
> +Some requirements for using fsl,imx-pinctrl binding:
> +1. We have pin function node defined under iomux controller node to represent
> +   what pinmux functions this SoC supports.
> +2. The pin configuration node intends to work on a specific function should
> +   to be defined under that specific function node.
> +   The function node's name should represent well about what function
> +   this group of pins in this pin configuration node are working on.
> +3. The driver can use the function node's name and pin configuration node's
> +   name describe the pin function and group hierarchy.
> +   For example, Linux IMX pinctrl driver takes the function node's name
> +   as the function name and pin configuration node's name as group name to
> +   create the map table.
> +4. Each pin configuration node should have a phandle, devices can set pins
> +   configurations by referring to the phandle of that pin configuration node.
> +
> +Examples:
> +usdhc@...9c000 { /* uSDHC4 */
> +	fsl,card-wired;
> +	vmmc-supply = <&reg_3p3v>;
> +	status = "okay";
> +	pinctrl-names = "default";
> +	pinctrl-0 = <&pinctrl_usdhc4_1>;
> +};
> +
> +iomuxc@...e0000 {
> +	compatible = "fsl,imx6q-iomuxc";
> +	reg = <0x020e0000 0x4000>;
> +
> +	/* shared pinctrl settings */
> +	usdhc4 {
> +		pinctrl_usdhc4_1: usdhc4grp-1 {
> +			fsl,pins = <1386 0x17059	/* MX6Q_PAD_SD4_CMD__USDHC4_CMD */
> +				    1392 0x17059	/* MX6Q_PAD_SD4_CLK__USDHC4_CLK	*/
> +				    1462 0x17059	/* MX6Q_PAD_SD4_DAT0__USDHC4_DAT0 */
> +				    1470 0x17059	/* MX6Q_PAD_SD4_DAT1__USDHC4_DAT1 */
> +				    1478 0x17059	/* MX6Q_PAD_SD4_DAT2__USDHC4_DAT2 */
> +				    1486 0x17059	/* MX6Q_PAD_SD4_DAT3__USDHC4_DAT3 */
> +				    1493 0x17059	/* MX6Q_PAD_SD4_DAT4__USDHC4_DAT4 */
> +				    1501 0x17059	/* MX6Q_PAD_SD4_DAT5__USDHC4_DAT5 */
> +				    1509 0x17059	/* MX6Q_PAD_SD4_DAT6__USDHC4_DAT6 */
> +				    1517 0x17059>;	/* MX6Q_PAD_SD4_DAT7__USDHC4_DAT7 */
honestly I don't like this it's obscure need to decode manually

I propose to use phandle

as example on uart you will want or not the rst/cts so you will have quite a
lot of bindings

so you can describe the pin configuration (function) and refer it by phandle
in the group

Best Regards,
J.
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