Commit | Line | Data |
---|---|---|
7e525b7d LW |
1 | Qualcomm External Bus Interface 2 (EBI2) |
2 | ||
3 | The EBI2 contains two peripheral blocks: XMEM and LCDC. The XMEM handles any | |
4 | external memory (such as NAND or other memory-mapped peripherals) whereas | |
5 | LCDC handles LCD displays. | |
6 | ||
7 | As it says it connects devices to an external bus interface, meaning address | |
8 | lines (up to 9 address lines so can only address 1KiB external memory space), | |
9 | data lines (16 bits), OE (output enable), ADV (address valid, used on some | |
10 | NOR flash memories), WE (write enable). This on top of 6 different chip selects | |
11 | (CS0 thru CS5) so that in theory 6 different devices can be connected. | |
12 | ||
13 | Apparently this bus is clocked at 64MHz. It has dedicated pins on the package | |
14 | and the bus can only come out on these pins, however if some of the pins are | |
15 | unused they can be left unconnected or remuxed to be used as GPIO or in some | |
16 | cases other orthogonal functions as well. | |
17 | ||
18 | Also CS1 and CS2 has -A and -B signals. Why they have that is unclear to me. | |
19 | ||
20 | The chip selects have the following memory range assignments. This region of | |
21 | memory is referred to as "Chip Peripheral SS FPB0" and is 168MB big. | |
22 | ||
23 | Chip Select Physical address base | |
24 | CS0 GPIO134 0x1a800000-0x1b000000 (8MB) | |
25 | CS1 GPIO39 (A) / GPIO123 (B) 0x1b000000-0x1b800000 (8MB) | |
26 | CS2 GPIO40 (A) / GPIO124 (B) 0x1b800000-0x1c000000 (8MB) | |
27 | CS3 GPIO133 0x1d000000-0x25000000 (128 MB) | |
28 | CS4 GPIO132 0x1c800000-0x1d000000 (8MB) | |
29 | CS5 GPIO131 0x1c000000-0x1c800000 (8MB) | |
30 | ||
31 | The APQ8060 Qualcomm Application Processor User Guide, 80-N7150-14 Rev. A, | |
32 | August 6, 2012 contains some incomplete documentation of the EBI2. | |
33 | ||
34 | FIXME: the manual mentions "write precharge cycles" and "precharge cycles". | |
35 | We have not been able to figure out which bit fields these correspond to | |
36 | in the hardware, or what valid values exist. The current hypothesis is that | |
37 | this is something just used on the FAST chip selects and that the SLOW | |
38 | chip selects are understood fully. There is also a "byte device enable" | |
39 | flag somewhere for 8bit memories. | |
40 | ||
41 | FIXME: The chipselects have SLOW and FAST configuration registers. It's a bit | |
42 | unclear what this means, if they are mutually exclusive or can be used | |
43 | together, or if some chip selects are hardwired to be FAST and others are SLOW | |
44 | by design. | |
45 | ||
46 | The XMEM registers are totally undocumented but could be partially decoded | |
47 | because the Cypress AN49576 Antioch Westbridge apparently has suspiciously | |
48 | similar register layout, see: http://www.cypress.com/file/105771/download | |
49 | ||
50 | Required properties: | |
51 | - compatible: should be one of: | |
52 | "qcom,msm8660-ebi2" | |
53 | "qcom,apq8060-ebi2" | |
2956b338 | 54 | - #address-cells: should be <2>: the first cell is the chipselect, |
7e525b7d LW |
55 | the second cell is the offset inside the memory range |
56 | - #size-cells: should be <1> | |
57 | - ranges: should be set to: | |
58 | ranges = <0 0x0 0x1a800000 0x00800000>, | |
59 | <1 0x0 0x1b000000 0x00800000>, | |
60 | <2 0x0 0x1b800000 0x00800000>, | |
61 | <3 0x0 0x1d000000 0x08000000>, | |
62 | <4 0x0 0x1c800000 0x00800000>, | |
63 | <5 0x0 0x1c000000 0x00800000>; | |
64 | - reg: two ranges of registers: EBI2 config and XMEM config areas | |
65 | - reg-names: should be "ebi2", "xmem" | |
66 | - clocks: two clocks, EBI_2X and EBI | |
2956b338 | 67 | - clock-names: should be "ebi2x", "ebi2" |
7e525b7d LW |
68 | |
69 | Optional subnodes: | |
70 | - Nodes inside the EBI2 will be considered device nodes. | |
71 | ||
72 | The following optional properties are properties that can be tagged onto | |
73 | any device subnode. We are assuming that there can be only ONE device per | |
e65e50ff | 74 | chipselect subnode, else the properties will become ambiguous. |
7e525b7d LW |
75 | |
76 | Optional properties arrays for SLOW chip selects: | |
77 | - qcom,xmem-recovery-cycles: recovery cycles is the time the memory continues to | |
78 | drive the data bus after OE is de-asserted, in order to avoid contention on | |
79 | the data bus. They are inserted when reading one CS and switching to another | |
80 | CS or read followed by write on the same CS. Valid values 0 thru 15. Minimum | |
81 | value is actually 1, so a value of 0 will still yield 1 recovery cycle. | |
82 | - qcom,xmem-write-hold-cycles: write hold cycles, these are extra cycles | |
83 | inserted after every write minimum 1. The data out is driven from the time | |
84 | WE is asserted until CS is asserted. With a hold of 1 (value = 0), the CS | |
85 | stays active for 1 extra cycle etc. Valid values 0 thru 15. | |
86 | - qcom,xmem-write-delta-cycles: initial latency for write cycles inserted for | |
87 | the first write to a page or burst memory. Valid values 0 thru 255. | |
88 | - qcom,xmem-read-delta-cycles: initial latency for read cycles inserted for the | |
89 | first read to a page or burst memory. Valid values 0 thru 255. | |
90 | - qcom,xmem-write-wait-cycles: number of wait cycles for every write access, 0=1 | |
91 | cycle. Valid values 0 thru 15. | |
92 | - qcom,xmem-read-wait-cycles: number of wait cycles for every read access, 0=1 | |
93 | cycle. Valid values 0 thru 15. | |
94 | ||
95 | Optional properties arrays for FAST chip selects: | |
96 | - qcom,xmem-address-hold-enable: this is a boolean property stating that we | |
97 | shall hold the address for an extra cycle to meet hold time requirements | |
98 | with ADV assertion. | |
99 | - qcom,xmem-adv-to-oe-recovery-cycles: the number of cycles elapsed before an OE | |
100 | assertion, with respect to the cycle where ADV (address valid) is asserted. | |
101 | 2 means 2 cycles between ADV and OE. Valid values 0, 1, 2 or 3. | |
102 | - qcom,xmem-read-hold-cycles: the length in cycles of the first segment of a | |
2956b338 | 103 | read transfer. For a single read transfer this will be the time from CS |
7e525b7d LW |
104 | assertion to OE assertion. Valid values 0 thru 15. |
105 | ||
106 | ||
107 | Example: | |
108 | ||
109 | ebi2@1a100000 { | |
110 | compatible = "qcom,apq8060-ebi2"; | |
111 | #address-cells = <2>; | |
112 | #size-cells = <1>; | |
113 | ranges = <0 0x0 0x1a800000 0x00800000>, | |
114 | <1 0x0 0x1b000000 0x00800000>, | |
115 | <2 0x0 0x1b800000 0x00800000>, | |
116 | <3 0x0 0x1d000000 0x08000000>, | |
117 | <4 0x0 0x1c800000 0x00800000>, | |
118 | <5 0x0 0x1c000000 0x00800000>; | |
119 | reg = <0x1a100000 0x1000>, <0x1a110000 0x1000>; | |
120 | reg-names = "ebi2", "xmem"; | |
121 | clocks = <&gcc EBI2_2X_CLK>, <&gcc EBI2_CLK>; | |
122 | clock-names = "ebi2x", "ebi2"; | |
123 | /* Make sure to set up the pin control for the EBI2 */ | |
124 | pinctrl-names = "default"; | |
125 | pinctrl-0 = <&foo_ebi2_pins>; | |
126 | ||
127 | foo-ebi2@2,0 { | |
128 | compatible = "foo"; | |
129 | reg = <2 0x0 0x100>; | |
130 | (...) | |
131 | qcom,xmem-recovery-cycles = <0>; | |
132 | qcom,xmem-write-hold-cycles = <3>; | |
133 | qcom,xmem-write-delta-cycles = <31>; | |
134 | qcom,xmem-read-delta-cycles = <28>; | |
135 | qcom,xmem-write-wait-cycles = <9>; | |
136 | qcom,xmem-read-wait-cycles = <9>; | |
137 | }; | |
138 | }; |