From mboxrd@z Thu Jan 1 00:00:00 1970 From: fjohnber@zoho.com (Fredrick) Date: Sun, 29 Jan 2012 05:27:30 -0800 Subject: kmalloc before kmem_cache_init In-Reply-To: References: Message-ID: <4F254942.30505@zoho.com> To: kernelnewbies@lists.kernelnewbies.org List-Id: kernelnewbies.lists.kernelnewbies.org 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 wrote: >> Hi Sukanto, >> >> On Sat, Jan 28, 2012 at 11:25 PM, Sukanto Ghosh >> 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