Re: [Question] which type of DMA taken by musb of beagle-xM(DM3730)?

[Anand Gadiyar <gadiyar@ti.com>]

On 10/27/2010 10:55 AM, Ming Lei wrote:
> 2010/10/27 Ming Lei<tom.leiming@gmail.com>:
>> Hi Gadiyar,
>>
>> Thanks for your reply.
>>
>> 2010/10/27 Gadiyar, Anand<gadiyar@ti.com>:
>>> On Wed, Oct 27, 2010 at 5:54 AM, Ming Lei<tom.leiming@gmail.com>  wrote:
>>>> I want to know which type of DMA is taken by musb of DM3730,
>>>> INVENTRA_DMA, TI_CPPI_DMA or others?
>>>
>>> Inventra DMA. An updated version compared to the OMAP34xx/35xx.
>>>
>>> - No major change to the programming model
>>> - The simultaneous TX-RX DMA hang bug is gone with this one.
>>
>> I find one issue about the dma transfer if Inventra DMA is used, seems
>> always 2 bytes less than required length, is it caused by unaligned
>> destination address?
>>
>> See the log captured in g_ether context:
>>

Ouch, yes. I'd forgotten about this one. I think I did post out patches 
for this. But I've moved to other activities and didn't follow up. I'll 
dig them up and  post in a bit.

The issue is that, by design, the last 2 bits of DMA_ADDR are masked by 
the DMA engine; so we need DMA_ADDR to be aligned to a 32-bit boundary.

In gadget mode, g_ether is one driver that's badly affected - there were 
some patches posted which improved g_ether somewhat. In host mode, 
USB-networking cases were most affected. MUSB has two options:

- dma_channel_program can reject transfers to unaligned DMA addresses, 
so that the backup PIO mode can take over (a quick fix - I'll post this 
one again)

- MUSB can bounce the transfer buffer to another buffer which is 
properly aligned

Any other ideas?

- Anand