Re: [PATCH 3/4] libata: add per-dev pio/mwdma/udma_mask

[Jeff Garzik <jgarzik@pobox.com>]

Tejun Heo wrote:
> On Mon, Mar 13, 2006 at 03:29:24AM -0500, Jeff Garzik wrote:
> 
>>Tejun Heo wrote:
>>
>>>Add per-dev pio/mwdma/udma_mask.  All transfer mode limits used to be
>>>applied to ap->*_mask which unnecessarily restricted other devices
>>>sharing the port.  This change will also benefit later EH speed down
>>>and hotplug.
>>>
>>>Signed-off-by: Tejun Heo <htejun@gmail.com>
>>
>>I don't see much value in the separation.  Rather than 3 separate masks, 
>>it seems like this patch would be simplified if you simply added 
>>dev->xfer_mask.
>>
> 
> 
> The thing is that ap->*_mask's are separated the same way and all
> masking constants are defined as such.  e.g.
> 
> 	ap->udma_mask &= ATA_UDMA5;
> or
> 	ap->udma_mask &= ATA_UDMA_MASK_40C;
> 
> Making dev->*_mask's the same enables share those constants and code
> convention.  So, things to consider here are...
> 
> 1. Port xfer masks are defined as three separate masks.
> 
> 2. All the constants are defined according to that.
> 
> 3. Three separate masks are easier to deal with for LLDD's.

Separate masks is better for the LLDD interface, but the packed version 
seems superior for internal libata use.

No reason why ATA_UDMA_MASK_40C can't simply operate on a packed 
xfer_mask variable, for example.

	Jeff