powerpc/pseries/iommu: Allow bigger 64bit window by removing default DMA window

On LoPAR "DMA Window Manipulation Calls", it's recommended to remove the
default DMA window for the device, before attempting to configure a DDW,
in order to make the maximum resources available for the next DDW to be
created.

This is a requirement for using DDW on devices in which hypervisor
allows only one DMA window.

If setting up a new DDW fails anywhere after the removal of this
default DMA window, it's needed to restore the default DMA window.
For this, an implementation of ibm,reset-pe-dma-windows rtas call is
needed:

Platforms supporting the DDW option starting with LoPAR level 2.7 implement
ibm,ddw-extensions. The first extension available (index 2) carries the
token for ibm,reset-pe-dma-windows rtas call, which is used to restore
the default DMA window for a device, if it has been deleted.

It does so by resetting the TCE table allocation for the PE to it's
boot time value, available in "ibm,dma-window" device tree node.
Signed-off-by: Leonardo Bras <leobras.c@gmail.com>
Tested-by: David Dai <zdai@linux.vnet.ibm.com>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200805030455.123024-5-leobras.c@gmail.com

arch/powerpc/platforms/pseries/iommu.c

@@ -1066,6 +1066,38 @@ static phys_addr_t ddw_memory_hotplug_max(void)
 	return max_addr;
 }
 
+/*
+ * Platforms supporting the DDW option starting with LoPAR level 2.7 implement
+ * ibm,ddw-extensions, which carries the rtas token for
+ * ibm,reset-pe-dma-windows.
+ * That rtas-call can be used to restore the default DMA window for the device.
+ */
+static void reset_dma_window(struct pci_dev *dev, struct device_node *par_dn)
+{
+	int ret;
+	u32 cfg_addr, reset_dma_win;
+	u64 buid;
+	struct device_node *dn;
+	struct pci_dn *pdn;
+
+	ret = ddw_read_ext(par_dn, DDW_EXT_RESET_DMA_WIN, &reset_dma_win);
+	if (ret)
+		return;
+
+	dn = pci_device_to_OF_node(dev);
+	pdn = PCI_DN(dn);
+	buid = pdn->phb->buid;
+	cfg_addr = (pdn->busno << 16) | (pdn->devfn << 8);
+
+	ret = rtas_call(reset_dma_win, 3, 1, NULL, cfg_addr, BUID_HI(buid),
+			BUID_LO(buid));
+	if (ret)
+		dev_info(&dev->dev,
+			 "ibm,reset-pe-dma-windows(%x) %x %x %x returned %d ",
+			 reset_dma_win, cfg_addr, BUID_HI(buid), BUID_LO(buid),
+			 ret);
+}
+
 /*
  * If the PE supports dynamic dma windows, and there is space for a table
  * that can map all pages in a linear offset, then setup such a table,
@@ -1090,6 +1122,7 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
 	struct property *win64;
 	struct dynamic_dma_window_prop *ddwprop;
 	struct failed_ddw_pdn *fpdn;
+	bool default_win_removed = false;
 
 	mutex_lock(&direct_window_init_mutex);
 
@@ -1133,14 +1166,38 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
 	if (ret != 0)
 		goto out_failed;
 
+	/*
+	 * If there is no window available, remove the default DMA window,
+	 * if it's present. This will make all the resources available to the
+	 * new DDW window.
+	 * If anything fails after this, we need to restore it, so also check
+	 * for extensions presence.
+	 */
 	if (query.windows_available == 0) {
-		/*
-		 * no additional windows are available for this device.
-		 * We might be able to reallocate the existing window,
-		 * trading in for a larger page size.
-		 */
-		dev_dbg(&dev->dev, "no free dynamic windows");
-		goto out_failed;
+		struct property *default_win;
+		int reset_win_ext;
+
+		default_win = of_find_property(pdn, "ibm,dma-window", NULL);
+		if (!default_win)
+			goto out_failed;
+
+		reset_win_ext = ddw_read_ext(pdn, DDW_EXT_RESET_DMA_WIN, NULL);
+		if (reset_win_ext)
+			goto out_failed;
+
+		remove_dma_window(pdn, ddw_avail, default_win);
+		default_win_removed = true;
+
+		/* Query again, to check if the window is available */
+		ret = query_ddw(dev, ddw_avail, &query, pdn);
+		if (ret != 0)
+			goto out_failed;
+
+		if (query.windows_available == 0) {
+			/* no windows are available for this device. */
+			dev_dbg(&dev->dev, "no free dynamic windows");
+			goto out_failed;
+		}
 	}
 	if (query.page_size & 4) {
 		page_shift = 24; /* 16MB */
@@ -1231,6 +1288,8 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
 	kfree(win64);
 
 out_failed:
+	if (default_win_removed)
+		reset_dma_window(dev, pdn);
 
 	fpdn = kzalloc(sizeof(*fpdn), GFP_KERNEL);
 	if (!fpdn)