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SubjectRe: [PATCH 1/2] hvc_xen: add earlycon support
Date
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@eu.citrix.com>
> ---
> 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);

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