diff options
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/spi/spi.h | 20 |
1 files changed, 13 insertions, 7 deletions
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h index b6bedc3ee95..1be5ea05947 100644 --- a/include/linux/spi/spi.h +++ b/include/linux/spi/spi.h @@ -341,9 +341,14 @@ extern struct spi_master *spi_busnum_to_master(u16 busnum); * chip transactions together. * * (ii) When the transfer is the last one in the message, the chip may - * stay selected until the next transfer. This is purely a performance - * hint; the controller driver may need to select a different device - * for the next message. + * stay selected until the next transfer. On multi-device SPI busses + * with nothing blocking messages going to other devices, this is just + * a performance hint; starting a message to another device deselects + * this one. But in other cases, this can be used to ensure correctness. + * Some devices need protocol transactions to be built from a series of + * spi_message submissions, where the content of one message is determined + * by the results of previous messages and where the whole transaction + * ends when the chipselect goes intactive. * * The code that submits an spi_message (and its spi_transfers) * to the lower layers is responsible for managing its memory. @@ -480,14 +485,15 @@ static inline void spi_message_free(struct spi_message *m) /** * spi_setup - setup SPI mode and clock rate * @spi: the device whose settings are being modified - * Context: can sleep + * Context: can sleep, and no requests are queued to the device * * SPI protocol drivers may need to update the transfer mode if the - * device doesn't work with the mode 0 default. They may likewise need + * device doesn't work with its default. They may likewise need * to update clock rates or word sizes from initial values. This function * changes those settings, and must be called from a context that can sleep. - * The changes take effect the next time the device is selected and data - * is transferred to or from it. + * Except for SPI_CS_HIGH, which takes effect immediately, the changes take + * effect the next time the device is selected and data is transferred to + * or from it. When this function returns, the spi device is deselected. * * Note that this call will fail if the protocol driver specifies an option * that the underlying controller or its driver does not support. For |