cxl: Introduce implementation-specific API

The backend API (in cxl.h) lists some low-level functions whose
implementation is different on bare-metal and in a guest. Each
environment implements its own functions, and the common code uses
them through function pointers, defined in cxl_backend_ops

Co-authored-by: Christophe Lombard <clombard@linux.vnet.ibm.com>
Signed-off-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Signed-off-by: Christophe Lombard <clombard@linux.vnet.ibm.com>
Reviewed-by: Manoj Kumar <manoj@linux.vnet.ibm.com>
Acked-by: Ian Munsie <imunsie@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

drivers/misc/cxl/main.c

@@ -32,6 +32,8 @@ uint cxl_verbose;
 module_param_named(verbose, cxl_verbose, uint, 0600);
 MODULE_PARM_DESC(verbose, "Enable verbose dmesg output");
 
+const struct cxl_backend_ops *cxl_ops;
+
 int cxl_afu_slbia(struct cxl_afu *afu)
 {
 	unsigned long timeout = jiffies + (HZ * CXL_TIMEOUT);
@@ -46,7 +48,7 @@ int cxl_afu_slbia(struct cxl_afu *afu)
 		/* If the adapter has gone down, we can assume that we
 		 * will PERST it and that will invalidate everything.
 		 */
-		if (!cxl_adapter_link_ok(afu->adapter))
+		if (!cxl_ops->link_ok(afu->adapter))
 			return -EIO;
 		cpu_relax();
 	}
@@ -228,7 +230,7 @@ struct cxl_afu *cxl_alloc_afu(struct cxl *adapter, int slice)
 
 	afu->adapter = adapter;
 	afu->dev.parent = &adapter->dev;
-	afu->dev.release = cxl_release_afu;
+	afu->dev.release = cxl_ops->release_afu;
 	afu->slice = slice;
 	idr_init(&afu->contexts_idr);
 	mutex_init(&afu->contexts_lock);
@@ -244,10 +246,10 @@ struct cxl_afu *cxl_alloc_afu(struct cxl *adapter, int slice)
 int cxl_afu_select_best_mode(struct cxl_afu *afu)
 {
 	if (afu->modes_supported & CXL_MODE_DIRECTED)
-		return cxl_afu_activate_mode(afu, CXL_MODE_DIRECTED);
+		return cxl_ops->afu_activate_mode(afu, CXL_MODE_DIRECTED);
 
 	if (afu->modes_supported & CXL_MODE_DEDICATED)
-		return cxl_afu_activate_mode(afu, CXL_MODE_DEDICATED);
+		return cxl_ops->afu_activate_mode(afu, CXL_MODE_DEDICATED);
 
 	dev_warn(&afu->dev, "No supported programming modes available\n");
 	/* We don't fail this so the user can inspect sysfs */
@@ -269,6 +271,7 @@ static int __init init_cxl(void)
 	if ((rc = register_cxl_calls(&cxl_calls)))
 		goto err;
 
+	cxl_ops = &cxl_native_ops;
 	if ((rc = pci_register_driver(&cxl_pci_driver)))
 		goto err1;