hostmot2 bspi: add hm2_bspi_clear_fifo()

The BSPI module has a receive fifo and a transmit fifo per instance
(shared among all the channels of that instance).

Writing anything to the fifo count register clears both fifos, discarding
any old read data and any pending write data.

Author: SebKuzminsky

src/hal/drivers/mesa-hostmot2/bspi.c

@@ -179,6 +179,26 @@ int hm2_allocate_bspi_tram(char* name)
     return 0;
 }
 
+EXPORT_SYMBOL_GPL(hm2_bspi_clear_fifo);
+int hm2_bspi_clear_fifo(char * name)
+{
+    hostmot2_t * hm2;
+    int i, r;
+
+    i = hm2_get_bspi(&hm2, name);
+    if (i < 0){
+        HM2_ERR_NO_LL("Can not find BSPI instance %s.\n", name);
+        return -1;
+    }
+    rtapi_u32 zero = 0;
+    r = hm2->llio->write(hm2->llio, hm2->bspi.instance[i].count_addr, &zero, sizeof(rtapi_u32));
+    if (r < 0) {
+        HM2_ERR("BSPI: hm2->llio->write failure %s\n", name);
+    }
+    
+    return r;
+}
+
 EXPORT_SYMBOL_GPL(hm2_bspi_write_chan);
 int hm2_bspi_write_chan(char* name, int chan, rtapi_u32 val)
 {

src/hal/drivers/mesa-hostmot2/hostmot2-serial.h

@@ -39,6 +39,7 @@ int hm2_bspi_set_write_function(char *name, int (*func)(void *subdata), void *su
 int hm2_bspi_write_chan(char* name, int chan, rtapi_u32 val);
 int hm2_allocate_bspi_tram(char* name);
 int hm2_tram_add_bspi_frame(char *name, int chan, rtapi_u32 **wbuff, rtapi_u32 **rbuff);
+int hm2_bspi_clear_fifo(char * name);
 
 RTAPI_END_DECLS
 

src/hal/drivers/mesa-hostmot2/hostmot2.h

@@ -1719,6 +1719,7 @@ int hm2_sserial_read_configs(hostmot2_t *hm2, hm2_sserial_remote_t *chan);
 int  hm2_bspi_parse_md(hostmot2_t *hm2, int md_index);
 void hm2_bspi_print_module(hostmot2_t *hm2);
 void hm2_bspi_cleanup(hostmot2_t *hm2);
+int hm2_bspi_clear_fifo(char * name);
 void hm2_bspi_write(hostmot2_t *hm2);
 void hm2_bspi_force_write(hostmot2_t *hm2);
 void hm2_bspi_prepare_tram_write(hostmot2_t *hm2, long period);