Re: Purpose of MMC_DATA_MULTI?

[Pierre Ossman <drzeus-list@drzeus.cx>]

Russell King wrote:
> On Wed, Feb 01, 2006 at 10:37:12AM +0100, Pierre Ossman wrote:
>   
> > Russell King wrote:
> >     
> > > On Wed, Feb 01, 2006 at 07:40:26AM +0100, Pierre Ossman wrote:
> > >       
> > > > I noticed that a new transfer flag was recently added to the MMC layer
> > > > without any immediate users, the MMC_DATA_MULTI flag. I'm guessing the
> > > > purpose of the flag is to indicate the difference between
> > > > MMC_READ_SINGLE_BLOCK and MMC_READ_MULTIPLE_BLOCKS with just one block.
> > > > If so, then that should probably be mentioned in a comment somewhere.
> > > >     
> > > >         
> > > There are hosts out there (Atmel AT91-based) which need to know if the
> > > transfer is going to be multiple block.  Rather than have them test
> > > the op-code (which is what they're already doing), we provide a flag
> > > instead.
> > >       
> > As far as the hardware is concerned there are two "multi-block" transfers:
> >
> >  * Multiple, back-to-back blocks.
> >  * One or more blocks that need to be terminated by some form of stop
> > command.
> >
> > The first can be identified by checking the number of blocks in the
> > request, the latter is harder to identify since it's a protocol semantic
> > (it could be just one block, but still need a stop). Does MMC_DATA_MULTI
> > indicate the latter, former or both?
> >     
>
> In short, it's defined to be whatever AT91_MCI_TRTYP_MULTIPLE means in
> the AT91RM9200 MMC host driver, which appears to be set for any of the
> multiple block commands.  They currently are doing:
>
>   

That's a bit fuzzy and bound to give problems. Why not settle for the 
first case and change their code to check the block count in the 
request? Less flags should be a good thing. And if that proves to be 
insufficient we should do a more thorough investigation once we have an 
actual failure case.

> and using that as a lookup table by command for the value to put into
> the command register.  I want to eliminate that, and not passing the
> MULTI flag prevents elimination of this table.
>
>   

Seems to be a common theme in the more recent drivers. Don't they teach 
people proper layering in the schools anymore? :)

Rgds
Pierre


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