[uClinux-dev] SCSI problem for USB mass storage devices

Erwin Authried eauth at softsys.co.at
Wed Oct 19 02:53:53 EDT 2005


On Wed, 2005-10-19 at 01:27, David McCullough wrote:

> 1) Make a big DMA zone and no normal zone,  possibly risk slowing down
>    normal allocations as they will switch to DMA if there is nothing else
>    to use.
> 
> 2) Not have a DMA zone
> 
> I think for "in kernel" use you actually want DMA to be the fastest
> allocation,  since net drivers and most HW will normally want DMA
> memory.  The only problem with 1 then would be most people would feel a
> little uncomfortable with only having DMA memory available :-)
> Also most !MMU systems don't use DMA.
> 
> So your solution below is ok,  but maybe a little too generic.  Some
> uClinux systems (who know what other processors do) may actually have a
> limited memory they can DMA from.  Or you may want to limit it to some
> faster memory ?
> 
what about making this 

#ifndef __GFP_DMA
#define __GFP_DMA       0x01
#endif

in linux/mm.h and defining __GFP_DMA in asm/arch/memory.h, if required?
That wouldn't break any architectures that make use of the "standard"
dma zone.

Regards,
Erwin


> Either way I am not to concerned about it,
> 
> Cheers,
> Davidm
> 
> 
> > > > #ifdef CONFIG_UCLINUX
> > > > #define  __GFP_DMA 0
> > > > #else
> > > > #define __GFP_DMA       0x01
> > > > #endif
> > > > 
> > > > Regards,
> > > > Erwin




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