[Xen-devel] [PATCH] xen/arm: domain_build: DT: add clocks node to the hypervisor node

[Dirk Behme <dirk.behme@xxxxxxxxxxxx>]

Some clocks might be used by Xen (drivers) and not by the Linux kernel. If
these are not registered by the Linux kernel, they might be disabled by the
Linux kernel's clk_disable_unused() as the kernel doesn't know that
they are used (by Xen drivers). The clock of the serial console handled by
Xen is one example for this. It might be disabled by clk_disable_unused() which
stops the whole serial output, even from Xen, then.

Up to now, the workaround for this has been to use the Linux kernel
command line parameter 'clk_ignore_unused'. See Xen bug

http://bugs.xenproject.org/xen/bug/45

too.

To fix this, add the clocks used by Xen to the hypervisor node. The Linux
kernel has to register the clocks from the hypervisor node, then.

Therefore, collect all clocks from nodes used by Xen. These are marked
with  DOMID_XEN. Afterwards, add a 'clocks' node to the hypervisor node
containing all these clocks. The Linux kernel can register all these clocks,
preventing them from being disabled, then.

Signed-off-by: Dirk Behme <dirk.behme@xxxxxxxxxxxx>
---
 xen/arch/arm/domain_build.c | 20 ++++++++++++++++++++
 xen/arch/arm/kernel.h       |  7 +++++++
 2 files changed, 27 insertions(+)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index 2e4c295..fccf87e 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -657,6 +657,10 @@ static int make_hypervisor_node(const struct kernel_info 
*kinfo,
     if ( res )
         return res;
 
+    res = fdt_property(fdt, "clocks", kinfo->clk.dtclocks, kinfo->clk.cnt);
+    if ( res )
+        return res;
+
     res = fdt_end_node(fdt);
 
     return res;
@@ -1213,9 +1217,11 @@ static int handle_node(struct domain *d, struct 
kernel_info *kinfo,
         { /* sentinel */ },
     };
     struct dt_device_node *child;
+    unsigned int len;
     int res;
     const char *name;
     const char *path;
+    const char *clocks;
 
     path = dt_node_full_name(node);
 
@@ -1246,6 +1252,20 @@ static int handle_node(struct domain *d, struct 
kernel_info *kinfo,
     if ( dt_device_used_by(node) == DOMID_XEN )
     {
         DPRINT("  Skip it (used by Xen)\n");
+
+        /*
+         * Remember the clock used by the skipped node
+         * We add it later to the hypervisor node to make the
+         * Linux kernel aware of its usage
+         */
+        clocks = dt_get_property(node, "clocks", &len);
+        if ( kinfo->clk.cnt + len >= MAX_DT_CLOCKS ) {
+            printk("Failed to remember the clock node of %s\n", path);
+            printk("Use the Linux kernel command 'clk_ignore_unused'\n");
+            return 0;
+        }
+        memcpy(&kinfo->clk.dtclocks[kinfo->clk.cnt], clocks, len);
+        kinfo->clk.cnt += len;
         return 0;
     }
 
diff --git a/xen/arch/arm/kernel.h b/xen/arch/arm/kernel.h
index c1b07d4..527b279 100644
--- a/xen/arch/arm/kernel.h
+++ b/xen/arch/arm/kernel.h
@@ -10,6 +10,12 @@
 #include <xen/device_tree.h>
 #include <asm/setup.h>
 
+#define MAX_DT_CLOCKS 256
+struct dtclk {
+        unsigned char dtclocks[MAX_DT_CLOCKS];
+        unsigned int cnt;
+};
+
 struct kernel_info {
 #ifdef CONFIG_ARM_64
     enum domain_type type;
@@ -18,6 +24,7 @@ struct kernel_info {
     void *fdt; /* flat device tree */
     paddr_t unassigned_mem; /* RAM not (yet) assigned to a bank */
     struct meminfo mem;
+    struct dtclk clk;
 
     /* kernel entry point */
     paddr_t entry;
-- 
2.8.0


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