Re: [Linux-ia64] Re: 64 Bits DMA Addresses for Alloc Consistent Interfaces.

From: James Bottomley <James.Bottomley_at_HansenPartnership.com>
Date: 2003-05-16 12:05:12
On Thu, 2003-05-15 at 18:39, David S. Miller wrote:
> My main point is that device attributes belong IN THE DEVICE
> not in some umpteenth new parameter to the DMA interfaces.
> 
> Just put consistent_dma_mask into the device struct next to
> the existing dma_mask, voila problem solved.
> 
> I have two major problems with the generic DMA interfaces
> and how they are being handled in general:
> 
> 1) Their use is entirely inappropriate in unary-bus devices.
>    There is no way someone can justify some PCI driver continually
>    asking itself whether it is a PCI device or not on each DMA
>    API call.

Where's that in the API?  The PA-RISC implementation copes with about
four different buses and nowhere does it have a switch trying to
ascertain which bus it's talking about (it uses the dev->platform_data
field to cache the relevant bus attributes).

> 2) Additions to the parameters in the interfaces is not given
>    enough thought.  Each new parameter you add is a discrete failure
>    of the API.  It was built to be simple, and new parameters do
>    nothing but add complexity.
> 
>    I cannot even fathom that someone would suggest to pass device
>    attributes into the DMA interfaces.  That is just garbage and
>    unnecessary bloat.

You mean like xadding gfp flags to the allocator?

> Finally, I see nobody tackling the real hard bugs we have in the DMA
> API.  These should be fixed first before adding random DMA behaviorial
> attributes.  For example, pci_dma_sync_*() sucks because it only syncs
> in one direction, device to cpu, there is nothing available to sync
> things back from cpu-->device.  This prevents MIPS from using the
> devices that need to do syncs without unmaps (eepro100 is but one
> example, USB host controller drivers want this too).

OK, I don't get this yet, doesn't DMA_TO_DEVICE do what you want?  what
am I missing?

James
Received on Thu May 15 19:10:49 2003

This archive was generated by hypermail 2.1.8 : 2005-08-02 09:20:14 EST