diff options
Diffstat (limited to 'Documentation/devicetree/bindings/bus/qcom,ebi2.txt')
| -rw-r--r-- | Documentation/devicetree/bindings/bus/qcom,ebi2.txt | 138 |
1 files changed, 138 insertions, 0 deletions
diff --git a/Documentation/devicetree/bindings/bus/qcom,ebi2.txt b/Documentation/devicetree/bindings/bus/qcom,ebi2.txt new file mode 100644 index 000000000000..920681f552db --- /dev/null +++ b/Documentation/devicetree/bindings/bus/qcom,ebi2.txt @@ -0,0 +1,138 @@ +Qualcomm External Bus Interface 2 (EBI2) + +The EBI2 contains two peripheral blocks: XMEM and LCDC. The XMEM handles any +external memory (such as NAND or other memory-mapped peripherals) whereas +LCDC handles LCD displays. + +As it says it connects devices to an external bus interface, meaning address +lines (up to 9 address lines so can only address 1KiB external memory space), +data lines (16 bits), OE (output enable), ADV (address valid, used on some +NOR flash memories), WE (write enable). This on top of 6 different chip selects +(CS0 thru CS5) so that in theory 6 different devices can be connected. + +Apparently this bus is clocked at 64MHz. It has dedicated pins on the package +and the bus can only come out on these pins, however if some of the pins are +unused they can be left unconnected or remuxed to be used as GPIO or in some +cases other orthogonal functions as well. + +Also CS1 and CS2 has -A and -B signals. Why they have that is unclear to me. + +The chip selects have the following memory range assignments. This region of +memory is referred to as "Chip Peripheral SS FPB0" and is 168MB big. + +Chip Select Physical address base +CS0 GPIO134 0x1a800000-0x1b000000 (8MB) +CS1 GPIO39 (A) / GPIO123 (B) 0x1b000000-0x1b800000 (8MB) +CS2 GPIO40 (A) / GPIO124 (B) 0x1b800000-0x1c000000 (8MB) +CS3 GPIO133 0x1d000000-0x25000000 (128 MB) +CS4 GPIO132 0x1c800000-0x1d000000 (8MB) +CS5 GPIO131 0x1c000000-0x1c800000 (8MB) + +The APQ8060 Qualcomm Application Processor User Guide, 80-N7150-14 Rev. A, +August 6, 2012 contains some incomplete documentation of the EBI2. + +FIXME: the manual mentions "write precharge cycles" and "precharge cycles". +We have not been able to figure out which bit fields these correspond to +in the hardware, or what valid values exist. The current hypothesis is that +this is something just used on the FAST chip selects and that the SLOW +chip selects are understood fully. There is also a "byte device enable" +flag somewhere for 8bit memories. + +FIXME: The chipselects have SLOW and FAST configuration registers. It's a bit +unclear what this means, if they are mutually exclusive or can be used +together, or if some chip selects are hardwired to be FAST and others are SLOW +by design. + +The XMEM registers are totally undocumented but could be partially decoded +because the Cypress AN49576 Antioch Westbridge apparently has suspiciously +similar register layout, see: http://www.cypress.com/file/105771/download + +Required properties: +- compatible: should be one of: + "qcom,msm8660-ebi2" + "qcom,apq8060-ebi2" +- #address-cells: shoule be <2>: the first cell is the chipselect, + the second cell is the offset inside the memory range +- #size-cells: should be <1> +- ranges: should be set to: + ranges = <0 0x0 0x1a800000 0x00800000>, + <1 0x0 0x1b000000 0x00800000>, + <2 0x0 0x1b800000 0x00800000>, + <3 0x0 0x1d000000 0x08000000>, + <4 0x0 0x1c800000 0x00800000>, + <5 0x0 0x1c000000 0x00800000>; +- reg: two ranges of registers: EBI2 config and XMEM config areas +- reg-names: should be "ebi2", "xmem" +- clocks: two clocks, EBI_2X and EBI +- clock-names: shoule be "ebi2x", "ebi2" + +Optional subnodes: +- Nodes inside the EBI2 will be considered device nodes. + +The following optional properties are properties that can be tagged onto +any device subnode. We are assuming that there can be only ONE device per +chipselect subnode, else the properties will become ambigous. + +Optional properties arrays for SLOW chip selects: +- qcom,xmem-recovery-cycles: recovery cycles is the time the memory continues to + drive the data bus after OE is de-asserted, in order to avoid contention on + the data bus. They are inserted when reading one CS and switching to another + CS or read followed by write on the same CS. Valid values 0 thru 15. Minimum + value is actually 1, so a value of 0 will still yield 1 recovery cycle. +- qcom,xmem-write-hold-cycles: write hold cycles, these are extra cycles + inserted after every write minimum 1. The data out is driven from the time + WE is asserted until CS is asserted. With a hold of 1 (value = 0), the CS + stays active for 1 extra cycle etc. Valid values 0 thru 15. +- qcom,xmem-write-delta-cycles: initial latency for write cycles inserted for + the first write to a page or burst memory. Valid values 0 thru 255. +- qcom,xmem-read-delta-cycles: initial latency for read cycles inserted for the + first read to a page or burst memory. Valid values 0 thru 255. +- qcom,xmem-write-wait-cycles: number of wait cycles for every write access, 0=1 + cycle. Valid values 0 thru 15. +- qcom,xmem-read-wait-cycles: number of wait cycles for every read access, 0=1 + cycle. Valid values 0 thru 15. + +Optional properties arrays for FAST chip selects: +- qcom,xmem-address-hold-enable: this is a boolean property stating that we + shall hold the address for an extra cycle to meet hold time requirements + with ADV assertion. +- qcom,xmem-adv-to-oe-recovery-cycles: the number of cycles elapsed before an OE + assertion, with respect to the cycle where ADV (address valid) is asserted. + 2 means 2 cycles between ADV and OE. Valid values 0, 1, 2 or 3. +- qcom,xmem-read-hold-cycles: the length in cycles of the first segment of a + read transfer. For a single read trandfer this will be the time from CS + assertion to OE assertion. Valid values 0 thru 15. + + +Example: + +ebi2@1a100000 { + compatible = "qcom,apq8060-ebi2"; + #address-cells = <2>; + #size-cells = <1>; + ranges = <0 0x0 0x1a800000 0x00800000>, + <1 0x0 0x1b000000 0x00800000>, + <2 0x0 0x1b800000 0x00800000>, + <3 0x0 0x1d000000 0x08000000>, + <4 0x0 0x1c800000 0x00800000>, + <5 0x0 0x1c000000 0x00800000>; + reg = <0x1a100000 0x1000>, <0x1a110000 0x1000>; + reg-names = "ebi2", "xmem"; + clocks = <&gcc EBI2_2X_CLK>, <&gcc EBI2_CLK>; + clock-names = "ebi2x", "ebi2"; + /* Make sure to set up the pin control for the EBI2 */ + pinctrl-names = "default"; + pinctrl-0 = <&foo_ebi2_pins>; + + foo-ebi2@2,0 { + compatible = "foo"; + reg = <2 0x0 0x100>; + (...) + qcom,xmem-recovery-cycles = <0>; + qcom,xmem-write-hold-cycles = <3>; + qcom,xmem-write-delta-cycles = <31>; + qcom,xmem-read-delta-cycles = <28>; + qcom,xmem-write-wait-cycles = <9>; + qcom,xmem-read-wait-cycles = <9>; + }; +}; |