Usually, the 16-bit rx length is read from scratch pad registers
with two CMD52 transactions:
SD8385: IF_SDIO_SCRATCH_OLD (0x80fe/0x80ff)
SD8686/SD8688: IF_SDIO_SCRATCH (0x34/0x35)
Alternatively, SD8688 firmware offers an enhanced method for driver
to read an 8-bit rx length (in units) with a single CMD52:
IF_SDIO_RX_UNIT 0x43 is read one time after firmware is ready.
IF_SDIO_RX_LEN 0x42 is read every time when rx interrupt is received.
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Acked-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
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