how to specify dma_mask and coherent_dma_mask in hwmod

[N, Mugunthan V]

> -----Original Message-----
> From: Russell King - ARM Linux [mailto:linux at arm.linux.org.uk]
> Sent: Wednesday, July 04, 2012 3:12 PM
> To: N, Mugunthan V
> Cc: linux-omap at vger.kernel.org; linux-arm-kernel at lists.infradead.org
> Subject: Re: how to specify dma_mask and coherent_dma_mask in hwmod
> 
> On Thu, Jun 07, 2012 at 04:22:17PM +0000, N, Mugunthan V wrote:
> > While converting platform device registry to Hwmod for CPSW Ethernet
> > driver which is present in AM335X (OMAP2+), I am not finding a way
> > to specify dma_mask and coherent_dma_mask.
> > Is there a way to specify dma_mask and coherent_dma_mask in hwmod?
> 
> Just remember that we're moving stuff to DMA engine, and that means
> the sDMA device has DMA masks, but none of the peripherals which make
> use of sDMA should have DMA masks set.
> 
> The reason for this is because the device responsible for accessing
> memory is sDMA, not the peripheral device, and therefore any memory
> properties for DMA should come from the sDMA device, not the peripheral
> device.

I agree that properties of DMA should come from sDMA device. In my case 
(CPSW Ethernet) has a peripheral DMA (davinci_cpdma) which takes care of 
transferring packet from memory to Ethernet IP and vice versa.

For allocating DMA memory space for davinci_cpdma, dma_alloc_coherent is 
used which requires dma_masks to be specified for the device.

To pass the dma_masks to the device following ways can be followed.
1. Extend omap_device_build arguments to hold dma_mask and coherent_dma_mask
   which will affect all other devices which uses omap_device_build api.
2. Hardcode the dma_mask and coherent_dma_mask in omap_device_build with 
   0xffffffff which can harm other devices
3. Specify the dma_mask and coherent_dma_mask after creating the device as
   done in musb device.
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=blob;f=arch/a
rm/mach-omap2/usb-musb.c;h=c4a576856661014ea3bec9acc70f80e32d62c33b;hb=HEAD

Regards,
Mugunthan V N