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

[Vitaly W. <vw...@ru...>]

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