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Diffstat (limited to 'Documentation/driver-api/soundwire/bra_cadence.rst')
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diff --git a/Documentation/driver-api/soundwire/bra_cadence.rst b/Documentation/driver-api/soundwire/bra_cadence.rst new file mode 100644 index 000000000000..4560752e8f47 --- /dev/null +++ b/Documentation/driver-api/soundwire/bra_cadence.rst @@ -0,0 +1,66 @@ +Cadence IP BRA support +---------------------- + +Format requirements +~~~~~~~~~~~~~~~~~~~ + +The Cadence IP relies on PDI0 for TX and PDI1 for RX. The data needs +to be formatted with the following conventions: + + (1) all Data is stored in bits 15..0 of the 32-bit PDI FIFOs. + + (2) the start of packet is BIT(31). + + (3) the end of packet is BIT(30). + + (4) A packet ID is stored in bits 19..16. This packet ID is + determined by software and is typically a rolling counter. + + (5) Padding shall be inserted as needed so that the Header CRC, + Header response, Footer CRC, Footer response are always in + Byte0. Padding is inserted by software for writes, and on reads + software shall discard the padding added by the hardware. + +Example format +~~~~~~~~~~~~~~ + +The following table represents the sequence provided to PDI0 for a +write command followed by a read command. + +:: + + +---+---+--------+---------------+---------------+ + + 1 | 0 | ID = 0 | WR HDR[1] | WR HDR[0] | + + | | | WR HDR[3] | WR HDR[2] | + + | | | WR HDR[5] | WR HDR[4] | + + | | | pad | WR HDR CRC | + + | | | WR Data[1] | WR Data[0] | + + | | | WR Data[3] | WR Data[2] | + + | | | WR Data[n-2] | WR Data[n-3] | + + | | | pad | WR Data[n-1] | + + 0 | 1 | | pad | WR Data CRC | + +---+---+--------+---------------+---------------+ + + 1 | 0 | ID = 1 | RD HDR[1] | RD HDR[0] | + + | | | RD HDR[3] | RD HDR[2] | + + | | | RD HDR[5] | RD HDR[4] | + + 0 | 1 | | pad | RD HDR CRC | + +---+---+--------+---------------+---------------+ + + +The table below represents the data received on PDI1 for the same +write command followed by a read command. + +:: + + +---+---+--------+---------------+---------------+ + + 1 | 0 | ID = 0 | pad | WR Hdr Rsp | + + 0 | 1 | | pad | WR Ftr Rsp | + +---+---+--------+---------------+---------------+ + + 1 | 0 | ID = 0 | pad | Rd Hdr Rsp | + + | | | RD Data[1] | RD Data[0] | + + | | | RD Data[3] | RD Data[2] | + + | | | RD HDR[n-2] | RD Data[n-3] | + + | | | pad | RD Data[n-1] | + + | | | pad | RD Data CRC | + + 0 | 1 | | pad | RD Ftr Rsp | + +---+---+--------+---------------+---------------+ |