linux-kernel - Re: [PATCH v3 4/6] powerpc/pseries/iommu: Remove default DMA window before creating DDW

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Message-ID: <846ba63b1f1fc4c9366f39b2cf09df71a19da891.camel@gmail.com>
Date:   Tue, 14 Jul 2020 03:46:29 -0300
From:   Leonardo Bras <leobras.c@...il.com>
To:     Alexey Kardashevskiy <aik@...abs.ru>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Ram Pai <linuxram@...ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/6] powerpc/pseries/iommu: Remove default DMA window
 before creating DDW

In fact, the changes over the last patch are more complex than the
current patch. 
Just for reference, that's how enable_ddw() currently patches:

@@ -1087,7 +1119,7 @@ static u64 enable_ddw(struct pci_dev *dev, struct
device_node *pdn)
        struct device_node *dn;
        u32 ddw_avail[DDW_APPLICABLE_SIZE];
        struct direct_window *window;
-       struct property *win64;
+       struct property *win64, *default_win = NULL;
        struct dynamic_dma_window_prop *ddwprop;
        struct failed_ddw_pdn *fpdn;
 
@@ -1133,14 +1165,38 @@ 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;
+               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) {
+                       default_win = NULL;
+                       goto out_failed;
+               }
+
+               remove_dma_window(pdn, ddw_avail, default_win);
+
+               /* 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 +1287,8 @@ static u64 enable_ddw(struct pci_dev *dev, struct
device_node *pdn)
        kfree(win64);
 
 out_failed:
+       if (default_win)
+               reset_dma_window(dev, pdn);
 
        fpdn = kzalloc(sizeof(*fpdn), GFP_KERNEL);
        if (!fpdn)