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Diffstat (limited to 'Documentation/devicetree/bindings/mtd/gpmc-nand.txt')
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diff --git a/Documentation/devicetree/bindings/mtd/gpmc-nand.txt b/Documentation/devicetree/bindings/mtd/gpmc-nand.txt new file mode 100644 index 000000000..a4a75fa79 --- /dev/null +++ b/Documentation/devicetree/bindings/mtd/gpmc-nand.txt @@ -0,0 +1,147 @@ +Device tree bindings for GPMC connected NANDs + +GPMC connected NAND (found on OMAP boards) are represented as child nodes of +the GPMC controller with a name of "nand". + +All timing relevant properties as well as generic gpmc child properties are +explained in a separate documents - please refer to +Documentation/devicetree/bindings/memory-controllers/omap-gpmc.txt + +For NAND specific properties such as ECC modes or bus width, please refer to +Documentation/devicetree/bindings/mtd/nand.txt + + +Required properties: + + - compatible: "ti,omap2-nand" + - reg: range id (CS number), base offset and length of the + NAND I/O space + - interrupts: Two interrupt specifiers, one for fifoevent, one for termcount. + +Optional properties: + + - nand-bus-width: Set this numeric value to 16 if the hardware + is wired that way. If not specified, a bus + width of 8 is assumed. + + - ti,nand-ecc-opt: A string setting the ECC layout to use. One of: + "sw" 1-bit Hamming ecc code via software + "hw" <deprecated> use "ham1" instead + "hw-romcode" <deprecated> use "ham1" instead + "ham1" 1-bit Hamming ecc code + "bch4" 4-bit BCH ecc code + "bch8" 8-bit BCH ecc code + "bch16" 16-bit BCH ECC code + Refer below "How to select correct ECC scheme for your device ?" + + - ti,nand-xfer-type: A string setting the data transfer type. One of: + + "prefetch-polled" Prefetch polled mode (default) + "polled" Polled mode, without prefetch + "prefetch-dma" Prefetch enabled DMA mode + "prefetch-irq" Prefetch enabled irq mode + + - elm_id: <deprecated> use "ti,elm-id" instead + - ti,elm-id: Specifies phandle of the ELM devicetree node. + ELM is an on-chip hardware engine on TI SoC which is used for + locating ECC errors for BCHx algorithms. SoC devices which have + ELM hardware engines should specify this device node in .dtsi + Using ELM for ECC error correction frees some CPU cycles. + - rb-gpios: GPIO specifier for the ready/busy# pin. + +For inline partition table parsing (optional): + + - #address-cells: should be set to 1 + - #size-cells: should be set to 1 + +Example for an AM33xx board: + + gpmc: gpmc@50000000 { + compatible = "ti,am3352-gpmc"; + ti,hwmods = "gpmc"; + reg = <0x50000000 0x36c>; + interrupts = <100>; + gpmc,num-cs = <8>; + gpmc,num-waitpins = <2>; + #address-cells = <2>; + #size-cells = <1>; + ranges = <0 0 0x08000000 0x1000000>; /* CS0 space, 16MB */ + elm_id = <&elm>; + interrupt-controller; + #interrupt-cells = <2>; + + nand@0,0 { + compatible = "ti,omap2-nand"; + reg = <0 0 4>; /* CS0, offset 0, NAND I/O window 4 */ + interrupt-parent = <&gpmc>; + interrupts = <0 IRQ_TYPE_NONE>, <1 IRQ_TYPE NONE>; + nand-bus-width = <16>; + ti,nand-ecc-opt = "bch8"; + ti,nand-xfer-type = "polled"; + rb-gpios = <&gpmc 0 GPIO_ACTIVE_HIGH>; /* gpmc_wait0 */ + + gpmc,sync-clk-ps = <0>; + gpmc,cs-on-ns = <0>; + gpmc,cs-rd-off-ns = <44>; + gpmc,cs-wr-off-ns = <44>; + gpmc,adv-on-ns = <6>; + gpmc,adv-rd-off-ns = <34>; + gpmc,adv-wr-off-ns = <44>; + gpmc,we-off-ns = <40>; + gpmc,oe-off-ns = <54>; + gpmc,access-ns = <64>; + gpmc,rd-cycle-ns = <82>; + gpmc,wr-cycle-ns = <82>; + gpmc,wr-access-ns = <40>; + gpmc,wr-data-mux-bus-ns = <0>; + + #address-cells = <1>; + #size-cells = <1>; + + /* partitions go here */ + }; + }; + +How to select correct ECC scheme for your device ? +-------------------------------------------------- +Higher ECC scheme usually means better protection against bit-flips and +increased system lifetime. However, selection of ECC scheme is dependent +on various other factors also like; + +(1) support of built in hardware engines. + Some legacy OMAP SoC do not have ELM harware engine, so those SoC cannot + support ecc-schemes with hardware error-correction (BCHx_HW). However + such SoC can use ecc-schemes with software library for error-correction + (BCHx_HW_DETECTION_SW). The error correction capability with software + library remains equivalent to their hardware counter-part, but there is + slight CPU penalty when too many bit-flips are detected during reads. + +(2) Device parameters like OOBSIZE. + Other factor which governs the selection of ecc-scheme is oob-size. + Higher ECC schemes require more OOB/Spare area to store ECC syndrome, + so the device should have enough free bytes available its OOB/Spare + area to accommodate ECC for entire page. In general following expression + helps in determining if given device can accommodate ECC syndrome: + "2 + (PAGESIZE / 512) * ECC_BYTES" <= OOBSIZE" + where + OOBSIZE number of bytes in OOB/spare area + PAGESIZE number of bytes in main-area of device page + ECC_BYTES number of ECC bytes generated to protect + 512 bytes of data, which is: + '3' for HAM1_xx ecc schemes + '7' for BCH4_xx ecc schemes + '14' for BCH8_xx ecc schemes + '26' for BCH16_xx ecc schemes + + Example(a): For a device with PAGESIZE = 2048 and OOBSIZE = 64 and + trying to use BCH16 (ECC_BYTES=26) ecc-scheme. + Number of ECC bytes per page = (2 + (2048 / 512) * 26) = 106 B + which is greater than capacity of NAND device (OOBSIZE=64) + Hence, BCH16 cannot be supported on given device. But it can + probably use lower ecc-schemes like BCH8. + + Example(b): For a device with PAGESIZE = 2048 and OOBSIZE = 128 and + trying to use BCH16 (ECC_BYTES=26) ecc-scheme. + Number of ECC bytes per page = (2 + (2048 / 512) * 26) = 106 B + which can be accommodated in the OOB/Spare area of this device + (OOBSIZE=128). So this device can use BCH16 ecc-scheme. |