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spi: Provide SPI_CS_WORD 

This provides a SPI operation mode which changes chip select after every
 word, used by some devices such as ADCs and DACs.
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Merge tag 'spi-cs-word' into spi-4.20

spi: Provide SPI_CS_WORD

This provides a SPI operation mode which changes chip select after every
word, used by some devices such as ADCs and DACs.
This commit is contained in:
Mark Brown 2018-09-17 14:17:30 -07:00
parent 3356d9f4cb cbaa62e009
commit 9263696677
2 changed files with 31 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

31
drivers/spi/spi.c
View File

@ -2774,8 +2774,10 @@ int spi_setup(struct spi_device *spi)
return -EINVAL;
/* help drivers fail *cleanly* when they need options
* that aren't supported with their current controller
* SPI_CS_WORD has a fallback software implementation,
* so it is ignored here.
*/
bad_bits = spi->mode & ~spi->controller->mode_bits;
bad_bits = spi->mode & ~(spi->controller->mode_bits | SPI_CS_WORD);
ugly_bits = bad_bits &
(SPI_TX_DUAL | SPI_TX_QUAD | SPI_RX_DUAL | SPI_RX_QUAD);
if (ugly_bits) {
@ -2829,6 +2831,33 @@ static int __spi_validate(struct spi_device *spi, struct spi_message *message)
if (list_empty(&message->transfers))
return -EINVAL;
/* If an SPI controller does not support toggling the CS line on each
* transfer (indicated by the SPI_CS_WORD flag), we can emulate it by
* splitting transfers into one-word transfers and ensuring that
* cs_change is set for each transfer.
*/
if ((spi->mode & SPI_CS_WORD) && !(ctlr->mode_bits & SPI_CS_WORD)) {
size_t maxsize;
int ret;
maxsize = (spi->bits_per_word + 7) / 8;
/* spi_split_transfers_maxsize() requires message->spi */
message->spi = spi;
ret = spi_split_transfers_maxsize(ctlr, message, maxsize,
GFP_KERNEL);
if (ret)
return ret;
list_for_each_entry(xfer, &message->transfers, transfer_list) {
/* don't change cs_change on the last entry in the list */
if (list_is_last(&xfer->transfer_list, &message->transfers))
break;
xfer->cs_change = 1;
}
}
/* Half-duplex links include original MicroWire, and ones with
* only one data pin like SPI_3WIRE (switches direction) or where
* either MOSI or MISO is missing. They can also be caused by

2
include/linux/spi/spi.h
View File

@ -163,6 +163,7 @@ struct spi_device {
#define SPI_TX_QUAD 0x200 /* transmit with 4 wires */
#define SPI_RX_DUAL 0x400 /* receive with 2 wires */
#define SPI_RX_QUAD 0x800 /* receive with 4 wires */
#define SPI_CS_WORD 0x1000 /* toggle cs after each word */
int irq;
void *controller_state;
void *controller_data;
@ -177,7 +178,6 @@ struct spi_device {
* the controller talks to each chip, like:
* - memory packing (12 bit samples into low bits, others zeroed)
* - priority
* - drop chipselect after each word
* - chipselect delays
* - ...
*/