Re: [Xen-devel] ARM Xen Bug #45: Is there a solution?

[Dirk Behme <dirk.behme@xxxxxxxxx>]

On 26.05.2016 11:00, Julien Grall wrote:
> On 25/05/2016 16:10, Dirk Behme wrote:
> > On 24.05.2016 22:05, Julien Grall wrote:
> > > On 24/05/2016 14:39, Dirk Behme wrote:
> > > > On 23.05.2016 22:15, Julien Grall wrote:
> > > > > Hello Dirk,
> > > > >
> > > > > > is there a solution for
> > > > > >
> > > > > > arm: domain 0 disables clocks which are in fact being used
> > > > > > http://bugs.xenproject.org/xen/bug/45
> > > > > >
> > > > > > ?
> > > > > >
> > > > > > On an ARM based board I have to use 'clk_ignore_unused' preventing
> > > > > > that
> > > > > > Dom0 disables the UART clock for the console UART configured with
> > > > > > console=hvc0.
> > > > > There is no better solution than passing "clk_ignore_unused" on the
> > > > > kernel command line so far.
> > > >
> > > > What would be the solution for this issue? The
> > > >
> > > > "propagate any clock related properties from the UART
> > > > node into the Xen hypervisor node"
> > > >
> > > > mentioned in the ticket?
> > > That is correct. Xen would copy the property "clocks" of the UART into
> > > the hypervisor node.
> > >
> > > DOM0 would then parse the clocks associated to this node and mark them
> > > as used by Xen (I think CLK_IGNORE_UNUSED could do the job for us).
> >
> > I've started to look into this:
> >
> > I'd think in arm_uart.c in dt_uart_init() after
> >
> > if ( !dev )
> >
> > we know the UART node we are looking for. From this we have to read the
> > clock configuration.
> >
> > To be clarified: How to read the clock configuration? I couldn't find
> > any convenient function dt_device_get_clock() or similar for that.
> Xen does not need to parse the content of the property "clocks" but
> copy the raw value to the DOM0 DT.
>
> You cand find the value of a property with dt_get_property.
>
> > Now, we have the clocks we are looking for.
> >
> > These are needed in domain_build.c in make_hypervisor_node(), then.
> >
> > To be clarified: How to pass the clock configuration from arm_uart.c to
> > domain_build.c (and not break the non-dt / non-ARM platforms)?
> >
> > Any ideas or comments?
> All the devices (UART included) used by Xen will return DOMID_XEN when
> dt_device_used_by is called to the node.
>
> You could use it to collect the clocks of all those devices and gather
> the value in a single property to be created in the hypervisor node.

Anything like below (untested) [1]?

I'm unhappy about the global variables and the max clocks, though.

Best regards

Dirk

[1]

---
 xen/arch/arm/domain_build.c |   24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

Index: xen.git/xen/arch/arm/domain_build.c
===================================================================
--- xen.git.orig/xen/arch/arm/domain_build.c
+++ xen.git/xen/arch/arm/domain_build.c
@@ -42,6 +42,10 @@ static void __init parse_dom0_mem(const
 }
 custom_param("dom0_mem", parse_dom0_mem);

+#define MAX_DT_CLOCKS 256
+static unsigned char dt_clocks[MAX_DT_CLOCKS];
+static unsigned int clk_cnt;
+
 //#define DEBUG_DT

 #ifdef DEBUG_DT
@@ -657,6 +661,10 @@ static int make_hypervisor_node(const st
     if ( res )
         return res;

+    res = fdt_property(fdt, "clocks", dt_clocks, clk_cnt);
+    if ( res )
+        return res;
+
     res = fdt_end_node(fdt);

     return res;
@@ -1213,9 +1221,11 @@ static int handle_node(struct domain *d,
         { /* 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 +1256,20 @@ static int handle_node(struct domain *d,
     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 ( 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(&dt_clocks[clk_cnt], clocks, len);
+        clk_cnt += len;
         return 0;
     }


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