Re: [PATCH] arm64: Add support to pass earlyprintk argument viadevice tree

From: Pranavkumar Sawargaonkar
Date: Mon Jun 10 2013 - 06:43:34 EST


Hi,

On 3 June 2013 21:21, Pranavkumar Sawargaonkar <pranavkumar@xxxxxxxxxx> 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@xxxxxxxxxx>
> Signed-off-by: Anup Patel <anup.patel@xxxxxxxxxx>
> ---
> 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@xxxxxxxxxxxxxxxx for comments.
Original RFC posted for this patch is:
https://patchwork.kernel.org/patch/2601411/

Thanks,
Pranav
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