Re: Compile error in ARM architecture

On Fri, Dec 11, 2009 at 07:41:21PM +0530, Bala Shanmugam wrote:
> Hi Russel,

Please take extra time with spelling peoples names, thanks.

> I am trying to compile linux kernel for ARM processor.
> I built arm toolchain [arm-linux-gcc] using BuildRoot.
>
> I am getting below compilation errors when I tried to build 2.6.31 and  
> latest 2.6.32-rc8 kernel.
>
> *Error 1:*
> CC [M]  drivers/scsi/advansys.o
> drivers/scsi/advansys.c:72:2: warning: #warning this driver is still not  
> properly converted to the DMA API
> drivers/scsi/advansys.c: In function 'advansys_get_sense_buffer_dma':
> drivers/scsi/advansys.c:8352: error: implicit declaration of function  
> 'dma_cache_sync'
>
> This error is because arm architecture doesn't support dma_cache_sync.
> Is it OK not to invoke it in arm?

We don't support the non-coherent DMA API on ARM yet - there seems to
only be one user of it, and I don't think anyone actually uses this
driver on ARM.

> *Error 2:*
> ERROR: "__bad_udelay" [sound/pci/ali5451/snd-ali5451.ko] undefined!
> ERROR: "__bad_udelay" [drivers/video/savage/savagefb.ko] undefined!
> ERROR: "__bad_udelay" [drivers/scsi/nsp32.ko] undefined!
> ERROR: "__bad_udelay" [drivers/scsi/atp870u.ko] undefined!
> ERROR: "__bad_udelay" [drivers/net/sungem.ko] undefined!
> ERROR: "__bad_udelay" [drivers/net/irda/donauboe.ko] undefined!
> ERROR: "__bad_udelay" [drivers/gpu/drm/radeon/radeon.ko] undefined!
> ERROR: "__bad_udelay" [drivers/atm/he.ko] undefined!
>
> udelay(int) function accepts value < 2000 in arm.  x86 supports < 20000.
> As above module uses udelay with value > 2000 an undefined function  
> [__bad_udelay] become part of these modules and above error is thrown.

Because of the limited nature of the calculation (which is basically
a fast divide by multiplying and shifting the result) for udelay() we
have a smaller upper limit.  As stated in the ARM udelay:

 * With currently imposed limits, this means that we support a max delay
 * of 2000us. Further limits: HZ<=1000 and bogomips<=3355

We certainly can't shave off a factor of 10 since that would mean we'd
have to refuse to run on any platform with a calculated bogomips in
excess of 335 - and we already have platforms in excess of these.

At the end of the day, large delays should not be done using udelay().
That's what mdelay() is for - m meaning millisecond.  Therefore, the
drivers wanting these millisecond delays should be using the proper
interface for long delays - that being mdelay().

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