Re: [PATCH/RFC] SPI: add DMAUNSAFE analog to David Brownell's core

[Vitaly Wool <vwool@ru.mvista.com>]

David Brownell wrote:

> Neither is it "remove" in the normal sense either.  The hot
> path never had an allocation before ... but it could easily
> have one now, because that sort of bounce-buffer semantic is
> what a DMA_UNSAFE flag demands from the lower levels.  (That's
> a key part part of the proposed change that's not included in
> this patch... making the chage look much smaller.)
>  
Makes no sense to me, sorry. What 'not included' changes are you talking 
about?

> How much of the reason you're arguing for this is because you
> have that WLAN stack that does some static allocation for I/O
> buffers?  Changing that to use dynamic allocation -- the more
> usual style -- should be easy.  But instead, you want all code
> in the SPI stack to need to worry about two different kinds of
> I/O memory:  the normal stuff, and the DMA-unsafe kind.  Not
>  
Err, this change also allows to get rid of ugly stuff in write_then_read.
It also allows to keep track of memory allocation in SPI controller 
driver withough hacky tricks.
And... it's not *all* the code; if it doesn't provide such means, it's 
also fine.

> just this WLAN code which for some reason started out using
> a nonportable scheme for allocating I/O buffers.
>  
I'm afraid I just can't understand what you mean by 'portable' here.

> It'd take a lot more persuasion to make me think that's a good
> idea.  That's the kind of subtle confusion that really promotes
> hard-to-find bugs in drivers, and lots of developer confusion.
>  
What hard-to-find bugs, I wonder?
And... I'm afraid that your core is unacceptable for us w/o the changes 
proposed.

Vitaly
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