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Date: Fri, 25 Apr 2014 15:59:45 +0800
From: Huang Shijie <b32955@freescale.com>
To: Kamal Dasu <kdasu.kdev@gmail.com>
Subject: Re: [PATCH v2] mtd: nand: Add support to use nand_base poi databuf
 as bounce buffer
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On Fri, Apr 25, 2014 at 03:43:13PM +0800, Huang Shijie wrote:
> On Thu, Apr 24, 2014 at 11:52:41PM -0400, Kamal Dasu wrote:
> > Huang,
> > 
> > "could you show us how do the driver use the highmem buffer?"
> > 
> > This is the stack on a BMIPS platform we are doing a read dma transaction.
> > drv_*  calls are from out of tree nand controller  driver. This
> I can read the driver since it is not in the l2-mtd. :(

s/can/can't/		

> 
> > example shows the driver trying to map
> > highmem virtual address(0xfe1141e0)  for DMA operation passed from
> 
> Which dma api do you use?

In the ARM platform, we use the sg_init_one to initialize the sg.

It can only convert the kmalloc memory, please see the code:

   #define __virt_to_phys(x)	((x) - PAGE_OFFSET + PHYS_OFFSET)

It does a linear convert for a kernel address.
So in the ARM platform, it can _NOT_ support the highmem which is not linear.


I am not familiar with MIPS.

I do not know how the MIPS convert the highmem address.

thanks
Huang Shijie