Hi Grant,

On 12 June 2013 18:58, Grant Likely grant.likely@secretlab.ca wrote:

On Mon, 3 Jun 2013 21:21:11 +0530, Pranavkumar Sawargaonkar pranavkumar@linaro.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@linaro.org Signed-off-by: Anup Patel anup.patel@linaro.org

I'm not a big fan of this. It seems to be short-circuiting around existing properties.

Agreed, but intention was to have a simple solution since it is just to be used for early printing/debugging. and also keep that in sync with existing method of specifying earlyprintk from command line.

The kernel /should/ be able to use the

linux,stdout-path property to determine what the earlyprintk device to use is.

For this there are two problems:

1. Early printk code gets initialized before un-flattening of a device tree. Hence trying to find out node from stdout-path is tricky as we do not have of_find_node_by_path available.

2. Current compatible strings in arm64 early printk code are not in synced (or different) from actual compatible strings used in drivers - e.g. for PL011 In earlyprintk code match name is just pl011 but in dts it is specified as "arm,pl011" Hence we will need multiple changes to implement it.

g.

Thanks, Pranav

...

---

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

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-- Grant Likely, B.Sc, P.Eng. Secret Lab Technologies, Ltd.