Re: dma_mask on scsi_calculate_bounce_limit

[Douglas Gilbert <dgilbert@interlog.com>]

On 10-11-19 01:41 AM, 王神 wrote:
> On Fri, Nov 19, 2010 at 6:22 AM, James Bottomley
> <James.Bottomley@suse.de>  wrote:
>> On Fri, 2010-11-19 at 01:54 +0800, 王神 wrote:
>>> On Thu, Nov 18, 2010 at 11:21 PM, James Bottomley
>>> <James.Bottomley@suse.de>  wrote:
>>>> On Thu, 2010-11-18 at 14:20 +0530, 王神 wrote:
>>>>> Hi
>>>>>
>>>>> I have enabled DMA for my host device and when i connect a scsi device
>>>>> to the host, it crashes in the following code..
>>>>>
>>>>> Function: scsi_calculate_bounce_limit
>>>>>
>>>>>   if (host_dev&&  host_dev->dma_mask)
>>>>>                  bounce_limit = *host_dev->dma_mask;
>>>>>
>>>>> "*dma_mask" is illegal pointer operation. I would like to understand
>>>>> is this known and is there reason behind such a code ?
>>>>
>>>> It likely means you're operating on a new architecture and its generic
>>>> devices haven't been set up correctly.
>>>
>>> Could you please more specific on what is generic devices haven't been
>>> setup properly...
>>
>> It means the architecture setup code left a NULL pointer in the generic
>> device which shouldn't be there ... without knowing which architecture
>> and seeing the code, it's pretty impossible to be more specific.
> 
> It is for ARM and the error is not due to NULL pointer. The code just
> checks if it is host mode + dma enabled and it access a normal
> interger variable with indirection causing the crash;
> 
> int dma_mask;
> 
> and accessing dma_mask as "*dma_mask" ??
> 
> Anything I am missing :O

Yes, supplying more information.

I'm familiar with AT91SAM9G20 which is an ARM based
microcontroller. The directory of interest in the kernel
source is arch/arm/mach-at91 and for the G20 the
at91sam9260_devices.c file defines its DMA masks for
its devices. In all cases that I can see the dma_mask is
the address of a u64 holding DMA_BIT_MASK(32) .

There are no real SCSI devices on the G20 but USB
might be regarded as SCSI "once removed". And the
USB devices on the G20 have dma_mask values as
described above.

Doug Gilbert

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