Unable to handle kernel paging request at virtual address ... while writing to frame buffer..

[Chan Kim]

During the initialization, the kernel writes to the frame buffer using printk and I can see it on the LCD.
But when I am writing in the busybox (which is user program seen from the kernel) using 'printf', this page error occurs.
For both printk and printf cases, the context table base is the same, but one(printk) is in context 0 while the otehr is in context 1.
(but all the contexts have the same pgd values in both cases, each with different value for printk and printf because they are different process.
and different threads in a process have different context I understand). The frame buffer address appears the same in both printk and printf.
I've got the frame buffer address using dma_alloc_writecombine function (I tried with dma_alloc_coherent, but it fails with error in our system).
I guess there should be some typical cases when this happens.  (I know the page fault routine should assign a virtual address for the page frame containing the frame buffer and connect it to the page table for the context but it could not handle it. I will delve into it anyway..)
Any hint? I hope somebody could shed some light to this problem.
Thanks,
Chan

________________________________
From : "Valdis.Kletnieks at vt.edu" <Valdis.Kletnieks at vt.edu>
Sent : 2014-03-28 01:29:21 ( +09:00 )
To : Chan Kim <ckim at etri.re.kr>
Cc : kernelnewbies at kernelnewbies.org <kernelnewbies at kernelnewbies.org>
Subject : Re: Unable to handle kernel paging request at virtual address ... while writing to frame buffer..

On Thu, 27 Mar 2014 08:55:10 -0000, Chan Kim said:
> I have this 'unable to handle kernel paging request at virtual address ...'
> when writing to the frame buffer.

That almost certainly means you tried to write to something other than
the actual frame buffer.
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