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hw/ssi: Document ssi_transfer() method

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A SPI transaction consists of shifting bit in sync with the CLK
line, writing on the MOSI (output) line / and reading MISO (input)
line.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Gustavo Romero <gustavo.romero@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
This commit is contained in:
Philippe Mathieu-Daudé 2025-08-12 15:36:05 +02:00
parent 7baa9c39fc
commit 831d75fd73
1 changed files with 14 additions and 0 deletions
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14
include/hw/ssi/ssi.h
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@ -38,6 +38,7 @@ struct SSIPeripheralClass {
/* if you have standard or no CS behaviour, just override transfer.
* This is called when the device cs is active (true by default).
* See ssi_transfer().
*/
uint32_t (*transfer)(SSIPeripheral *dev, uint32_t val);
/* called when the CS line changes. Optional, devices only need to implement
@ -52,6 +53,7 @@ struct SSIPeripheralClass {
* of the CS behaviour at the device level. transfer, set_cs, and
* cs_polarity are unused if this is overwritten. Transfer_raw will
* always be called for the device for every txrx access to the parent bus
* See ssi_transfer().
*/
uint32_t (*transfer_raw)(SSIPeripheral *dev, uint32_t val);
};
@ -110,6 +112,18 @@ bool ssi_realize_and_unref(DeviceState *dev, SSIBus *bus, Error **errp);
/* Master interface. */
SSIBus *ssi_create_bus(DeviceState *parent, const char *name);
/**
* Transfer a word on a SSI bus
* @bus: SSI bus
* @val: word to transmit
*
* At the same time, read a word and write the @val one on the SSI bus.
*
* SSI words might vary between 8 and 32 bits. The same number of bits
* written is received.
*
* Return: word value received
*/
uint32_t ssi_transfer(SSIBus *bus, uint32_t val);
DeviceState *ssi_get_cs(SSIBus *bus, uint8_t cs_index);