[Xen-devel] [PATCH 4/4] dt-uart: support /chosen/stdout-path property.

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

ePAPR v1.1 section 3.5 defines the /chosen/stdout-path property to
refer to the device to be used for boot console output, so if no
dtuart property is given try to use that instead. This will make Xen
find a suitable console by default on DT platforms which include this
property.

As it happens the dtuart option has the exact same syntax as
stdout-path, so we can just copy the value into that buffer if it is
empty.

FWIW support for this was added to Linux in v3.19-rc1 (7914a7c5651a
"of: support passing console options with stdout-path") and a fairly
large number of the dts files shipped with Linux have already included
a stdout-path property for quite a while now.

Since there is a base of existing device trees with the property, we
do not support the legacy ',' options separator so we remain
compatible.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
 xen/arch/arm/domain_build.c |    2 ++
 xen/drivers/char/dt-uart.c  |   29 +++++++++++++++++++++++++++--
 2 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index de180d8..c33a73c 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -424,6 +424,7 @@ static int write_properties(struct domain *d, struct 
kernel_info *kinfo,
          *   bootargs (from module #1, above).
          * * remove bootargs,  xen,dom0-bootargs, xen,xen-bootargs,
          *   linux,initrd-start and linux,initrd-end.
+         * * remove stdout-path.
          * * remove bootargs, linux,uefi-system-table,
          *   linux,uefi-mmap-start, linux,uefi-mmap-size,
          *   linux,uefi-mmap-desc-size, and linux,uefi-mmap-desc-ver
@@ -434,6 +435,7 @@ static int write_properties(struct domain *d, struct 
kernel_info *kinfo,
             if ( dt_property_name_is_equal(prop, "xen,xen-bootargs") ||
                  dt_property_name_is_equal(prop, "linux,initrd-start") ||
                  dt_property_name_is_equal(prop, "linux,initrd-end") ||
+                 dt_property_name_is_equal(prop, "stdout-path") ||
                  dt_property_name_is_equal(prop, "linux,uefi-system-table") ||
                  dt_property_name_is_equal(prop, "linux,uefi-mmap-start") ||
                  dt_property_name_is_equal(prop, "linux,uefi-mmap-size") ||
diff --git a/xen/drivers/char/dt-uart.c b/xen/drivers/char/dt-uart.c
index 54e65fc..08b0d76 100644
--- a/xen/drivers/char/dt-uart.c
+++ b/xen/drivers/char/dt-uart.c
@@ -22,6 +22,7 @@
 #include <xen/console.h>
 #include <xen/device_tree.h>
 #include <xen/serial.h>
+#include <xen/errno.h>
 
 /*
  * Configure UART port with a string:
@@ -38,7 +39,7 @@ void __init dt_uart_init(void)
 {
     struct dt_device_node *dev;
     int ret;
-    const char *devpath = opt_dtuart;
+    const char *devpath = opt_dtuart, *stdout = NULL;
     char *options;
 
     if ( !console_has("dtuart") )
@@ -46,12 +47,36 @@ void __init dt_uart_init(void)
 
     if ( !strcmp(opt_dtuart, "") )
     {
+        struct dt_device_node *chosen = dt_find_node_by_path("/chosen");
+
+        if ( chosen )
+        {
+            ret = dt_property_read_string(chosen, "stdout-path", &stdout);
+            if ( ret >= 0 )
+            {
+                printk("Taking dtuart configuration from 
/chosen/stdout-path\n");
+                strlcpy(opt_dtuart, stdout, sizeof(opt_dtuart));
+            }
+            else if ( ret != -EINVAL /* Not present */ )
+                printk("Failed to read /chosen/stdout-path (%d)\n", ret);
+        }
+    }
+
+    if ( !strcmp(opt_dtuart, "") )
+    {
         printk("No dtuart path configured\n");
         return;
     }
 
     options = strchr(opt_dtuart, ':');
-    if ( !options )
+    /*
+     * Support ',' as a legacy separator for path from command line
+     * only, since there is no legacy on the Xen side with stdout-path
+     * and looking for ',' there would render us incompatible with
+     * many of the device tree files out there which already include a
+     * stdout-path.
+     */
+    if ( !options && !stdout )
         options = strchr(opt_dtuart, ',');
     if ( options != NULL )
         *(options++) = '\0';
-- 
1.7.10.4


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