ssi: Implemented CS behaviour

Added default CS behaviour for SSI slaves. SSI devices can set a property
to enable CS behaviour which will create a GPIO on the device which is the
CS. Tristating of the bus on SSI transfers is implemented.

Signed-off-by: Peter A. G. Crosthwaite <peter.crosthwaite@petalogix.com>
Acked-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 37 insertions, 0 deletions

diff --git a/hw/ssi.h b/hw/ssi.h
index 06657d7c16..65b159dcab 100644
--- a/hw/ssi.h
+++ b/hw/ssi.h
@@ -23,21 +23,58 @@ typedef struct SSISlave SSISlave;
 #define SSI_SLAVE_GET_CLASS(obj) \
      OBJECT_GET_CLASS(SSISlaveClass, (obj), TYPE_SSI_SLAVE)
 
+typedef enum {
+    SSI_CS_NONE = 0,
+    SSI_CS_LOW,
+    SSI_CS_HIGH,
+} SSICSMode;
+
 /* Slave devices.  */
 typedef struct SSISlaveClass {
     DeviceClass parent_class;
 
     int (*init)(SSISlave *dev);
+
+    /* if you have standard or no CS behaviour, just override transfer.
+     * This is called when the device cs is active (true by default).
+     */
     uint32_t (*transfer)(SSISlave *dev, uint32_t val);
+    /* called when the CS line changes. Optional, devices only need to implement
+     * this if they have side effects associated with the cs line (beyond
+     * tristating the txrx lines).
+     */
+    int (*set_cs)(SSISlave *dev, bool select);
+    /* define whether or not CS exists and is active low/high */
+    SSICSMode cs_polarity;
+
+    /* if you have non-standard CS behaviour override this to take control
+     * 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
+     */
+    uint32_t (*transfer_raw)(SSISlave *dev, uint32_t val);
 } SSISlaveClass;
 
 struct SSISlave {
     DeviceState qdev;
+
+    /* Chip select state */
+    bool cs;
 };
 
 #define SSI_SLAVE_FROM_QDEV(dev) DO_UPCAST(SSISlave, qdev, dev)
 #define FROM_SSI_SLAVE(type, dev) DO_UPCAST(type, ssidev, dev)
 
+extern const VMStateDescription vmstate_ssi_slave;
+
+#define VMSTATE_SSI_SLAVE(_field, _state) {                          \
+    .name       = (stringify(_field)),                               \
+    .size       = sizeof(SSISlave),                                  \
+    .vmsd       = &vmstate_ssi_slave,                                \
+    .flags      = VMS_STRUCT,                                        \
+    .offset     = vmstate_offset_value(_state, _field, SSISlave),    \
+}
+
 DeviceState *ssi_create_slave(SSIBus *bus, const char *name);
 
 /* Master interface.  */