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spi_bus_lock(9) [centos man page]

SPI_BUS_LOCK(9) 					  Serial Peripheral Interface (S					   SPI_BUS_LOCK(9)

NAME
spi_bus_lock - obtain a lock for exclusive SPI bus usage SYNOPSIS
int spi_bus_lock(struct spi_master * master); ARGUMENTS
master SPI bus master that should be locked for exclusive bus access CONTEXT
can sleep DESCRIPTION
This call may only be used from a context that may sleep. The sleep is non-interruptible, and has no timeout. This call should be used by drivers that require exclusive access to the SPI bus. The SPI bus must be released by a spi_bus_unlock call when the exclusive access is over. Data transfer must be done by spi_sync_locked and spi_async_locked calls when the SPI bus lock is held. It returns zero on success, else a negative error code. COPYRIGHT
Kernel Hackers Manual 3.10 June 2014 SPI_BUS_LOCK(9)

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STRUCT 
SPI_MASTER(9) Serial Peripheral Interface (S STRUCT SPI_MASTER(9) NAME
struct_spi_master - interface to SPI master controller SYNOPSIS
struct spi_master { struct device dev; struct list_head list; s16 bus_num; u16 num_chipselect; u16 dma_alignment; u16 mode_bits; u32 bits_per_word_mask; u16 flags; #define SPI_MASTER_HALF_DUPLEX BIT(0) #define SPI_MASTER_NO_RX BIT(1) #define SPI_MASTER_NO_TX BIT(2) spinlock_t bus_lock_spinlock; struct mutex bus_lock_mutex; bool bus_lock_flag; int (* setup) (struct spi_device *spi); int (* transfer) (struct spi_device *spi,struct spi_message *mesg); void (* cleanup) (struct spi_device *spi); bool queued; struct kthread_worker kworker; struct task_struct * kworker_task; struct kthread_work pump_messages; spinlock_t queue_lock; struct list_head queue; struct spi_message * cur_msg; bool busy; bool running; bool rt; int (* prepare_transfer_hardware) (struct spi_master *master); int (* transfer_one_message) (struct spi_master *master,struct spi_message *mesg); int (* unprepare_transfer_hardware) (struct spi_master *master); int * cs_gpios; }; MEMBERS
dev device interface to this driver list link with the global spi_master list bus_num board-specific (and often SOC-specific) identifier for a given SPI controller. num_chipselect chipselects are used to distinguish individual SPI slaves, and are numbered from zero to num_chipselects. each slave has a chipselect signal, but it's common that not every chipselect is connected to a slave. dma_alignment SPI controller constraint on DMA buffers alignment. mode_bits flags understood by this controller driver bits_per_word_mask A mask indicating which values of bits_per_word are supported by the driver. Bit n indicates that a bits_per_word n+1 is suported. If set, the SPI core will reject any transfer with an unsupported bits_per_word. If not set, this value is simply ignored, and it's up to the individual driver to perform any validation. flags other constraints relevant to this driver bus_lock_spinlock spinlock for SPI bus locking bus_lock_mutex mutex for SPI bus locking bus_lock_flag indicates that the SPI bus is locked for exclusive use setup updates the device mode and clocking records used by a device's SPI controller; protocol code may call this. This must fail if an unrecognized or unsupported mode is requested. It's always safe to call this unless transfers are pending on the device whose settings are being modified. transfer adds a message to the controller's transfer queue. cleanup frees controller-specific state queued whether this master is providing an internal message queue kworker thread struct for message pump kworker_task pointer to task for message pump kworker thread pump_messages work struct for scheduling work to the message pump queue_lock spinlock to syncronise access to message queue queue message queue cur_msg the currently in-flight message busy message pump is busy running message pump is running rt whether this queue is set to run as a realtime task prepare_transfer_hardware a message will soon arrive from the queue so the subsystem requests the driver to prepare the transfer hardware by issuing this call transfer_one_message the subsystem calls the driver to transfer a single message while queuing transfers that arrive in the meantime. When the driver is finished with this message, it must call spi_finalize_current_message so the subsystem can issue the next transfer unprepare_transfer_hardware there are currently no more messages on the queue so the subsystem notifies the driver that it may relax the hardware by issuing this call cs_gpios Array of GPIOs to use as chip select lines; one per CS number. Any individual value may be -ENOENT for CS lines that are not GPIOs (driven by the SPI controller itself). DESCRIPTION
Each SPI master controller can communicate with one or more spi_device children. These make a small bus, sharing MOSI, MISO and SCK signals but not chip select signals. Each device may be configured to use a different clock rate, since those shared signals are ignored unless the chip is selected. The driver for an SPI controller manages access to those devices through a queue of spi_message transactions, copying data between CPU memory and an SPI slave device. For each such message it queues, it calls the message's completion function when the transaction completes. COPYRIGHT
Kernel Hackers Manual 3.10 June 2014 STRUCT SPI_MASTER(9)

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