On Wed, Jul 10, 2013 at 01:27:52PM -0600, Stephen Warren wrote:
> On 07/08/2013 07:02 AM, Christian Ruppert wrote:
> ...
> > OK, a small drawing of our hardware should make this clear, let's take
> > an imaginary example of one port with 10 pins, one i2c interface, one
> > spi interface and one GPIO bank:
> >
> > | mux N-1|
> > +........+
> > | | 2
> > | +--/-- i2c
> > | |
> > 10 | | 4
> > Pins --/--+ mux N +--/-- spi
> > | |
> > | | 10
> > | +--/-- GPIO
> > | |
> > +........+
> > | mux N+1|
> >
> > This example shows the mux N inside the pin controller. It controls
> > all pins associated to port N through a single register value M. Let's
> > assume the pins are configured as follows in function of the register
> > value:
> >
> > pin M=0 M=1 M=2 M=3
> > 0 GPIO0 SPI_MISO GPIO0 SPI_MISO
> > 1 GPIO1 SPI_MOSI GPIO1 SPI_MOSI
> > 2 GPIO2 SPI_CK GPIO2 SPI_CK
> > 3 GPIO3 SPI_CS GPIO3 SPI_CS
> > 4 GPIO4 GPIO4 GPIO4 GPIO4
> > 5 GPIO5 GPIO5 GPIO5 GPIO5
> > 6 GPIO6 GPIO6 GPIO6 GPIO6
> > 7 GPIO7 GPIO7 GPIO7 GPIO7
> > 8 GPIO8 GPIO8 I2C_SDA I2C_SDA
> > 9 GPIO9 GPIO9 I2C_SCL I2C_SCL
>
>
> In that scenario, in the language of Linux's pinctrl subsystem, what you
> have is:
>
> 10 pins, named 0..9
> 1 pin group, named perhaps "mux N".
> 4 different functions; values M==0, 1, 2, 3.
>
> > We now have three pin groups defined, corresponding to the chip-side
> > ports of the pin controller:
> > GPIO = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
> > SPI = {0, 1, 2, 3}
> > I2C = {8, 9}
>
> You would usually only define pin groups for the pin/ball/package side
> of the pinmux HW. IIRC, you're also wanting to define pin groups for the
> intra-chip side of the pinmux HW. However, you're not muxing functions
> onto those pingroups; they're just there to help with naming the
> GPIO<->pinmux mapping. You only mux functions onto the pin/ball/package
> side pins/pingroups.
Well, the GPIO<->pinmux mapping is not the only reason for defining
these groups wrt. the chip-side of the pin controller. The other reasons
are:
- Make different interfaces on the same MUX orthogonal wrt. each
other, i.e. make it possible to request one independently of the
other. In the example above, SPI and I2C can be requested completely
independently and the pin controller driver decides which mode to
use.
- Make pin allocation more fine-grained (in the example above, only
pins 0-4 are "allocated" in case SPI is requested). This makes
GPIO<->interface pin conflict management more natural.
BTW: When managing conflicts between hardware interfaces and GPIOs,
this scheme actually leads to _less_ pin groups than if we defined
one group at the pin side and four different modes:
chip-side groups: GPIO, SPI, I2C
=> 3 groups.
pin-side groups: MUX_N, GPIOS_M0, GPIOS_M1, GPIOS_M2, GPIOS_M3
in our special case MUX_N and GPIOS_M0 are the
same.
=> 4 groups (or 5 in the general case).
It is true that GPIO_Mx don't need to be named but they need to be
defined inside the driver nevertheless.
> > abilis,pingrp now specifies one of the three pin groups. Note that I2C
> > and SPI can be requested independently in a completely orthogonal
> > manner: The information if I2C is reqired or not is confined to
> > the I2C request and does not leak into the SPI request as would
> > be the case if we configured the entire port at the same time.
>
> The pingrp should represent the pin/ball/package side pins/groups. In
> this case, it should specify "N".
>
> > abilis,ioport specifies N.
>
> That is replaced be pingrp.
>
> > abilis,ioconf specifies M.
>
> That'd be better named "function" or something like that, in order to
> indicate that it specifies which function is mux'd onto the specified
> pin(s)/pingroup(s).
--
Christian Ruppert , <christian.ruppert@xxxxxxxxxx>
/|
Tel: +41/(0)22 816 19-42 //| 3, Chemin du Pré-Fleuri
_// | bilis Systems CH-1228 Plan-les-Ouates
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