linux-kernel - Re: [PATCH] of: support passing console options with stdout-path

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Message-ID: <20141125103504.GA21525@leverpostej>
Date:	Tue, 25 Nov 2014 10:35:04 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Leif Lindholm <leif.lindholm@...aro.org>
Cc:	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"plagnioj@...osoft.com" <plagnioj@...osoft.com>,
	"ijc@...ian.org" <ijc@...ian.org>
Subject: Re: [PATCH] of: support passing console options with stdout-path

Hi Leif,

On Mon, Nov 24, 2014 at 10:23:58PM +0000, Leif Lindholm wrote:
> Support specifying console options (like with console=ttyXN,<options>)
> by appending them to the stdout-path property after a separating ':'.
> 
> Example:
> 	stdout-path = "uart0:115200";

I would very much like to be able to use this -- it will allow
distributions to boot on a board without having to know _anything_ about
the console UART until userspace is up, which would make it possible to
have a completely generic installer image, without requiring the
platform to provide bootargs.

My only concern is that this conflates the set of kernel command line
options for the UART wit the DT binding for it. I don't know how good
people are at keeping those options stable, and I know they are
currently not documented -- we would need to add a stdout-path options
section to relevant UART bindings.

Thanks,
Mark.

> 
> This patch also modifies of_find_node_by_path() to match only the
> portion of the path before a ':'.
> 
> Signed-off-by: Leif Lindholm <leif.lindholm@...aro.org>
> ---
>  drivers/of/base.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 3823edf..89c6b33 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -37,6 +37,7 @@ EXPORT_SYMBOL(of_allnodes);
>  struct device_node *of_chosen;
>  struct device_node *of_aliases;
>  struct device_node *of_stdout;
> +static char *of_stdout_options;
>  
>  struct kset *of_kset;
>  
> @@ -703,6 +704,8 @@ static struct device_node *__of_find_node_by_path(struct device_node *parent,
>  	if (!len)
>  		return NULL;
>  
> +	len = strchrnul(path, ':') - path;
> +
>  	__for_each_child_of_node(parent, child) {
>  		const char *name = strrchr(child->full_name, '/');
>  		if (WARN(!name, "malformed device_node %s\n", child->full_name))
> @@ -747,6 +750,8 @@ struct device_node *of_find_node_by_path(const char *path)
>  		if (!of_aliases)
>  			return NULL;
>  
> +		len = strchrnul(path, ':') - path;
> +
>  		for_each_property_of_node(of_aliases, pp) {
>  			if (strlen(pp->name) == len && !strncmp(pp->name, path, len)) {
>  				np = of_find_node_by_path(pp->value);
> @@ -1830,8 +1835,12 @@ void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align))
>  			name = of_get_property(of_chosen, "linux,stdout-path", NULL);
>  		if (IS_ENABLED(CONFIG_PPC) && !name)
>  			name = of_get_property(of_aliases, "stdout", NULL);
> -		if (name)
> +		if (name) {
>  			of_stdout = of_find_node_by_path(name);
> +			of_stdout_options = strchr(name, ':');
> +			if (of_stdout_options != NULL)
> +				of_stdout_options++;
> +		}
>  	}
>  
>  	if (!of_aliases)
> @@ -1957,7 +1966,7 @@ bool of_console_check(struct device_node *dn, char *name, int index)
>  {
>  	if (!dn || dn != of_stdout || console_set_on_cmdline)
>  		return false;
> -	return !add_preferred_console(name, index, NULL);
> +	return !add_preferred_console(name, index, of_stdout_options);
>  }
>  EXPORT_SYMBOL_GPL(of_console_check);
>  
> -- 
> 1.9.1
> 
> 
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