Re: [PATCH 1/2] hvc_xen: add earlycon support

From: Boris Ostrovsky
Date: Wed Feb 24 2016 - 09:43:19 EST


On 02/24/2016 07:23 AM, Stefano Stabellini wrote:
Introduce EARLYCON support in hvc_xen, useful for early debugging on arm
and arm64, where xen early_printk is not available. Differently from
xenboot_write_console on x86, we won't just return if !xen_pv_domain(),
because arm and arm64 guests are actually xen_hvm_domain() from linux
pov, and also because we want to capture all possible writes, including
the ones earlier than xen_early_init().

Signed-off-by: Stefano Stabellini<stefano.stabellini@xxxxxxxxxxxxx>
---
drivers/tty/hvc/hvc_xen.c | 48 ++++++++++++++++++++++++++++++++++-----------
1 file changed, 37 insertions(+), 11 deletions(-)

diff --git a/drivers/tty/hvc/hvc_xen.c b/drivers/tty/hvc/hvc_xen.c
index fa816b7..34e8e9f 100644
--- a/drivers/tty/hvc/hvc_xen.c
+++ b/drivers/tty/hvc/hvc_xen.c
@@ -25,6 +25,7 @@
#include <linux/init.h>
#include <linux/types.h>
#include <linux/list.h>
+#include <linux/serial_core.h>
#include <asm/io.h>
#include <asm/xen/hypervisor.h>
@@ -597,21 +598,11 @@ static int xen_cons_init(void)
}
console_initcall(xen_cons_init);
-#ifdef CONFIG_EARLY_PRINTK
-static void xenboot_write_console(struct console *console, const char *string,
- unsigned len)
+static void domU_write_early_console(const char *string, unsigned len)
{
unsigned int linelen, off = 0;
const char *pos;
- if (!xen_pv_domain())
- return;
-
- dom0_write_console(0, string, len);
-
- if (xen_initial_domain())
- return;
-
domU_write_console(0, "(early) ", 8);
while (off < len && NULL != (pos = strchr(string+off, '\n'))) {
linelen = pos-string+off;
@@ -625,6 +616,21 @@ static void xenboot_write_console(struct console *console, const char *string,
domU_write_console(0, string+off, len-off);
}
+#ifdef CONFIG_EARLY_PRINTK
+static void xenboot_write_console(struct console *console, const char *string,
+ unsigned len)
+{
+ if (!xen_pv_domain())
+ return;

This, BTW, will break PVHv2 code (which is not there yet). Your patch is not making the code any different from what it is now but I wonder whether xenboot_write_console() can be made to work for HVM guests at this time since you making changes there anyway.

Or we can delay it until HVMlite/PVHv2 patches make it in.

+
+ dom0_write_console(0, string, len);
+
+ if (xen_initial_domain())
+ return;
+
+ domU_write_early_console(string, len);
+}
+
struct console xenboot_console = {
.name = "xenboot",
.write = xenboot_write_console,
@@ -664,3 +670,23 @@ void xen_raw_printk(const char *fmt, ...)
xen_raw_console_write(buf);
}
+
+static void xenboot_earlycon_write(struct console *console,
+ const char *string,
+ unsigned len)
+{
+ dom0_write_console(0, string, len);
+
+ if (xen_initial_domain())
+ return;
+
+ domU_write_early_console(string, len);
+}

xenboot_earlycon_write() and xenboot_write_console() share most of the code, can it be factored out?

-boris

+
+static int __init xenboot_earlycon_setup(struct earlycon_device *device,
+ const char *opt)
+{
+ device->con->write = xenboot_earlycon_write;
+ return 0;
+}
+EARLYCON_DECLARE(xenboot, xenboot_earlycon_setup);