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spi/dw_spi: conditional transfer mode changes 

This allows the switching between transfer modes between 'transmit only',
'receive only' and 'transmit and receive' modes. Due to the design of the SPI
block, changing transfer modes requires that the block be disabled; in doing
so the chipselect line is inherently deasserted and (usually) the attached
device discards its state. Consequentially, switching modes requires that a
platform-specific chipselect function has been defined so that the chipselect
is not dropped during the change.

Signed-off-by: George Shore <george@georgeshore.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
This commit is contained in:
George Shore 2010-01-21 11:40:52 +00:00 committed by Grant Likely
parent f4aec798ae
commit 052dc7c45d
1 changed files with 16 additions and 0 deletions
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16
drivers/spi/dw_spi.c
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@ -537,6 +537,22 @@ static void pump_transfers(unsigned long data)
}
message->state = RUNNING_STATE;
/*
* Adjust transfer mode if necessary. Requires platform dependent
* chipselect mechanism.
*/
if (dws->cs_control) {
if (dws->rx && dws->tx)
chip->tmode = 0x00;
else if (dws->rx)
chip->tmode = 0x02;
else
chip->tmode = 0x01;
cr0 &= ~(0x3 << SPI_MODE_OFFSET);
cr0 |= (chip->tmode << SPI_TMOD_OFFSET);
}
/* Check if current transfer is a DMA transaction */
dws->dma_mapped = map_dma_buffers(dws);