Re: [PATCH RFC] usb: musb: fail unaligned DMA transfers on v1.8 and above

[Anand Gadiyar <gadiyar@ti.com>]

On 10/31/2010 3:29 PM, Ming Lei wrote:
> 2010/10/31 Anand Gadiyar<gadiyar@ti.com>:
>> The Inventra DMA engine in version 1.8 and later of the MUSB
>> controller cannot handle DMA addresses that are not aligned
>> to a 4 byte boundary. It ends up ignoring the last two bits
>> programmed in the DMA_ADDR register. This is a deliberate
>> design change in the controller and is documented in the
>> programming guide.
>>
>> Earlier versions of the controller could handle these
>> accesses just fine.
>>
>> Fail dma_channel_program if we see an unaligned address when
>> using the newer controllers, so that the caller can carry out
>> the transfer using PIO mode.
>> (Current callers already have this backup path in place).
>>
>> Signed-off-by: Anand Gadiyar<gadiyar@ti.com>
>> Cc: Felipe Balbi<balbi@ti.com>
>> Cc: Ming Lei<tom.leiming@gmail.com>
>> Cc: Ajay Kumar Gupta<ajay.gupta@ti.com>
>> Cc: Mike Frysinger<vapier@gentoo.org>
>
> Tested-by: Ming Lei<tom.leiming@gmail.com>
>
> This patch is verified OK about g_ether function on beagle xM board,
> but the revised patch "usb: musb: gadget: Unmapping the dma buffer
> when switching to PIO mode" [1] should be applied first.
>
>> ---
>> Patch based on linux-next as of 20101029.
>>
>> I believe Blackfin is also affected by this, but I'm not sure how
>> they're working around this. Mike?
>
> MUSB on Blackfin will fallback to PIO too, so no any working around
> for it, right?
>

I meant Blackfin should also have hit this issue so far. I'm making
a change based on the MUSB revision - so this change will affect 
Blackfin for sure - they use revision 1.9 and 2.0 I think. So I'm just 
wondering if they really are affected, or they've simply never hit this 
scenario before.

- Anand