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1 | SPI NOR framework |
2 | ============================================ | |
3 | ||
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4 | Part I - Why do we need this framework? |
5 | --------------------------------------- | |
1ef39108 | 6 | |
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7 | SPI bus controllers (drivers/spi/) only deal with streams of bytes; the bus |
8 | controller operates agnostic of the specific device attached. However, some | |
9 | controllers (such as Freescale's QuadSPI controller) cannot easily handle | |
10 | arbitrary streams of bytes, but rather are designed specifically for SPI NOR. | |
1ef39108 | 11 | |
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12 | In particular, Freescale's QuadSPI controller must know the NOR commands to |
13 | find the right LUT sequence. Unfortunately, the SPI subsystem has no notion of | |
14 | opcodes, addresses, or data payloads; a SPI controller simply knows to send or | |
15 | receive bytes (Tx and Rx). Therefore, we must define a new layering scheme under | |
16 | which the controller driver is aware of the opcodes, addressing, and other | |
17 | details of the SPI NOR protocol. | |
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18 | |
19 | Part II - How does the framework work? | |
254592db | 20 | -------------------------------------- |
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21 | |
22 | This framework just adds a new layer between the MTD and the SPI bus driver. | |
23 | With this new layer, the SPI NOR controller driver does not depend on the | |
24 | m25p80 code anymore. | |
25 | ||
26 | Before this framework, the layer is like: | |
27 | ||
28 | MTD | |
29 | ------------------------ | |
30 | m25p80 | |
31 | ------------------------ | |
32 | SPI bus driver | |
33 | ------------------------ | |
34 | SPI NOR chip | |
35 | ||
36 | After this framework, the layer is like: | |
37 | MTD | |
38 | ------------------------ | |
39 | SPI NOR framework | |
40 | ------------------------ | |
41 | m25p80 | |
42 | ------------------------ | |
43 | SPI bus driver | |
44 | ------------------------ | |
45 | SPI NOR chip | |
46 | ||
254592db | 47 | With the SPI NOR controller driver (Freescale QuadSPI), it looks like: |
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48 | MTD |
49 | ------------------------ | |
50 | SPI NOR framework | |
51 | ------------------------ | |
52 | fsl-quadSPI | |
53 | ------------------------ | |
54 | SPI NOR chip | |
55 | ||
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56 | Part III - How can drivers use the framework? |
57 | --------------------------------------------- | |
1ef39108 | 58 | |
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59 | The main API is spi_nor_scan(). Before you call the hook, a driver should |
60 | initialize the necessary fields for spi_nor{}. Please see | |
61 | drivers/mtd/spi-nor/spi-nor.c for detail. Please also refer to fsl-quadspi.c | |
62 | when you want to write a new driver for a SPI NOR controller. | |
8dee1d97 HZ |
63 | Another API is spi_nor_restore(), this is used to restore the status of SPI |
64 | flash chip such as addressing mode. Call it whenever detach the driver from | |
65 | device or reboot the system. |