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<dhylands@xxxxxxxxx> wrote:
>> Hi Sukanto,
>>
>> On Sat, Jan 28, 2012 at 11:25 PM, Sukanto Ghosh
>> <sukanto.cse.iitb@xxxxxxxxx> wrote:
>>> 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
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