linux-kernel - Re: [PATCH] arm64: Add support to pass earlyprintk argument via device tree

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Message-ID: <CAAHg+HiWNumV52BmiGmWyGTq7a=JH5O2ptQuHt7ywjnWzUYcvg@mail.gmail.com>
Date:	Mon, 10 Jun 2013 16:13:27 +0530
From:	Pranavkumar Sawargaonkar <pranavkumar@...aro.org>
To:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Cc:	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	Patch Tracking <patches@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Pranavkumar Sawargaonkar <pranavkumar@...aro.org>,
	Anup Patel <anup.patel@...aro.org>,
	devicetree-discuss@...ts.ozlabs.org
Subject: Re: [PATCH] arm64: Add support to pass earlyprintk argument via
 device tree

Hi,

On 3 June 2013 21:21, Pranavkumar Sawargaonkar <pranavkumar@...aro.org> wrote:
> This patch adds support for defining and passing earlyprintk
> related information i.e. device and address information via
> device tree by adding it inside "chosen" node.
>
> This will help user to just specify "earlyprintk" from bootargs
> without actually knowing the address and device to enable
> earlyprintk.
>
> Mechanism:
>
> One can just append earlyprintk=device-type,address (same as we pass
> through command line) in "/chosen" node to notify kernel which is the
> earlyprintk device and what is its address.
>
> Backward Compatibility:
>
> This patch also allows existing method of specifying earlyprintk
> parameter via bootargs.
>
> Existing method i.e. passing via bootargs will still have precedence
> over device tree i.e. if one specifies earlyprintk=device-type,address
> in bootargs then kernel will use information from bootargs instead of
> device tree.
>
> If user just specifies earlyprintk (without =...) then kernel will
> look for device tree earlyprintk parameter.
>
> Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@...aro.org>
> Signed-off-by: Anup Patel <anup.patel@...aro.org>
> ---
>  arch/arm64/kernel/early_printk.c |    7 +++++++
>  arch/arm64/kernel/setup.c        |   21 ++++++++++++++++++++-
>  2 files changed, 27 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/early_printk.c b/arch/arm64/kernel/early_printk.c
> index fbb6e18..4e6f845 100644
> --- a/arch/arm64/kernel/early_printk.c
> +++ b/arch/arm64/kernel/early_printk.c
> @@ -29,6 +29,8 @@
>  static void __iomem *early_base;
>  static void (*printch)(char ch);
>
> +extern char *earlyprintk_dt_args;
> +
>  /*
>   * PL011 single character TX.
>   */
> @@ -116,6 +118,11 @@ static int __init setup_early_printk(char *buf)
>         phys_addr_t paddr = 0;
>
>         if (!buf) {
> +               /* Try to check if Device Tree has this argument or not ? */
> +               buf = earlyprintk_dt_args;
> +       }
> +
> +       if (!buf) {
>                 pr_warning("No earlyprintk arguments passed.\n");
>                 return 0;
>         }
> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
> index 6a9a532..fb2d56f 100644
> --- a/arch/arm64/kernel/setup.c
> +++ b/arch/arm64/kernel/setup.c
> @@ -60,6 +60,8 @@ EXPORT_SYMBOL(processor_id);
>  unsigned int elf_hwcap __read_mostly;
>  EXPORT_SYMBOL_GPL(elf_hwcap);
>
> +char *earlyprintk_dt_args;
> +
>  static const char *cpu_name;
>  static const char *machine_name;
>  phys_addr_t __fdt_pointer __initdata;
> @@ -122,6 +124,23 @@ static void __init setup_processor(void)
>         elf_hwcap = 0;
>  }
>
> +int __init early_init_dt_scan_chosen_arm64(unsigned long node,
> +                                          const char *uname,
> +                                          int depth, void *data)
> +{
> +       char *prop;
> +
> +       /* Check if this is chosen node */
> +       if (early_init_dt_scan_chosen(node, uname, depth, data) == 0)
> +               return 0;
> +
> +       prop = of_get_flat_dt_prop(node, "earlyprintk", NULL);
> +       if (prop)
> +               earlyprintk_dt_args = prop;
> +
> +       return 1;
> +}
> +
>  static void __init setup_machine_fdt(phys_addr_t dt_phys)
>  {
>         struct boot_param_header *devtree;
> @@ -165,7 +184,7 @@ static void __init setup_machine_fdt(phys_addr_t dt_phys)
>         pr_info("Machine: %s\n", machine_name);
>
>         /* Retrieve various information from the /chosen node */
> -       of_scan_flat_dt(early_init_dt_scan_chosen, boot_command_line);
> +       of_scan_flat_dt(early_init_dt_scan_chosen_arm64, boot_command_line);
>         /* Initialize {size,address}-cells info */
>         of_scan_flat_dt(early_init_dt_scan_root, NULL);
>         /* Setup memory, calling early_init_dt_add_memory_arch */
> --
> 1.7.9.5
>

Ccing to devicetree-discuss@...ts.ozlabs.org for comments.
Original RFC posted for this patch is:
https://patchwork.kernel.org/patch/2601411/

Thanks,
Pranav
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