kmalloc before kmem_cache_init

On 01/29/2012 04:29 AM, Sukanto Ghosh wrote:

So to use a MMIO based 8250 as "earlycon", either we need to have some
sort of fixmap
(as in case of x86) or otherwise we need to have a ioremap_nocache()
version that works
even before kmem_cache_init() is called.
I am not sure how many architectures will have such form of ioremap
other than maybe
nommu variants.

Some architectures check for mem_init_done.
Probably every architecture must provide an "early_ioremap" function to 
be used in early _code_.

Greg,

Has anyone used the ioremap path so far ? If not, then why have it
there as usual ioremap
can be used only after mm_init(), but this driver whenever used will
get called earlier than that ?

Regards,
Sukanto



On Sun, Jan 29, 2012 at 3:03 PM, Dave Hylands[off-list ref]  wrote:

quoted

Hi Sukanto,

On Sat, Jan 28, 2012 at 11:25 PM, Sukanto Ghosh
[off-list ref]  wrote:

quoted

Hi Dave,

If you look into start_kernel() the call to parse_early_param()
precedes mm_init().
parse_early_param() eventually calls do_early_param().
do_early_param() parses for "earlycon" in kernel commandline and then calls the
setup_function associated with earlycon.

I have in my commandline: earlycon=uart8250,mmio32,0x10000000,9600

Call flow starting from drivers/tty/serial/8250_early.c will lead to kmalloc

early_param("early_con", setup_early_serial8250_console)
   setup_early_serial8250_console()
       early_serial8250_setup()
           parse_options()
               ioremap_nocache()
                  ... arch-specific-ioremap
                        -- some form of arch specific __ioremap_caller
                            --- get_vm_area_caller()
                                  __get_vm_area_node
                                       kzalloc_node
                                           kmalloc_node
                                                kmalloc

It looks like CONFIG_FIX_EARLYCON_MEM defaults to y (on x86 anyways),
so this would cause the path that doesn't call ioremam_nocache to be
taken.

I'm guessing that if you specify earycon, then you also need to ensure
that CONFIG_FIX_EARLYCON is set.

You didn't mention which architecture you were using. ARM has an
early_printk which is sort of like an early console.

--
Dave Hylands
Shuswap, BC, Canada
http://www.davehylands.com

-Fredrick