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spi: core: allow defining time that cs is deasserted as a multiple of SCK 

Support setting a delay between cs assert and deassert as
a multiple of spi clock length.

Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Martin Sperl 2019-02-23 08:49:50 +00:00 committed by Mark Brown
parent 0ff2de8bb1
commit d5864e5bed
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GPG Key ID: 24D68B725D5487D0
2 changed files with 9 additions and 0 deletions
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8
drivers/spi/spi.c
View File

@ -1111,6 +1111,7 @@ static void _spi_transfer_cs_change_delay(struct spi_message *msg,
{
u32 delay = xfer->cs_change_delay;
u32 unit = xfer->cs_change_delay_unit;
u32 hz;
/* return early on "fast" mode - for everything but USECS */
if (!delay && unit != SPI_DELAY_UNIT_USECS)
@ -1126,6 +1127,13 @@ static void _spi_transfer_cs_change_delay(struct spi_message *msg,
break;
case SPI_DELAY_UNIT_NSECS: /* nothing to do here */
break;
case SPI_DELAY_UNIT_SCK:
/* if there is no effective speed know, then approximate
* by underestimating with half the requested hz
*/
hz = xfer->effective_speed_hz ?: xfer->speed_hz / 2;
delay *= DIV_ROUND_UP(1000000000, hz);
break;
default:
dev_err_once(&msg->spi->dev,
"Use of unsupported delay unit %i, using default of 10us\n",

1
include/linux/spi/spi.h
View File

@ -831,6 +831,7 @@ struct spi_transfer {
u8 cs_change_delay_unit;
#define SPI_DELAY_UNIT_USECS 0
#define SPI_DELAY_UNIT_NSECS 1
#define SPI_DELAY_UNIT_SCK 2
u32 speed_hz;
u16 word_delay;