Re: [Qemu-devel] [RFC] Floppy controller: break relation with PC-style DMA

[Blue Swirl]

On 11/22/08, Hervé Poussineau <address@hidden> wrote:
> Blue Swirl a écrit :
>
> > On 11/22/08, Hervé Poussineau <address@hidden> wrote:
> >
> > > Hi,
> > >
> > >  Currently, floppy disk controller is tied to PC-style DMA controller.
> > >  Attached patch is an attempt to break the link between those, by
> > > introducing function pointers for dma operations (read, write, hold,
> > > release).
> > >
> >
> > Isn't it possible to move the i8257 DMA helpers to for example dma.c?
> > Then I could eliminate some dummy DMA_xx functions from sun4m.c and I
> > think fdctrl_i8257_init would not be needed.
> >
>
>  That's a little bit hard for 3 reasons:
>  a) i8257_dma_hold() checks if DMA is well programmed before doing the
> transfer. I suppose the check should be moved to DMA engine, or at least to
> the _read and _write handlers.

The DMA engine should be a better place.

>  b) There is also the problem at initialization, where each i8257 client
> calls DMA_register_channel() to register itself, and gives a callback
> function (fdctrl_transfer_handler for fdc.c).

How about pushing registering of the callback to board level, for
example introduce a function for getting the transfer callback.

>  c) This callback will then be called to feed destination DMA buffer part by
> part (see dma_pos and dma_len in fdctrl_transfer_handler), instead of in one
> big transfer. That also explains the data_pos parameter when calling
> DMA_read_memory/DMA_write_memory

There is something fishy with the interface, real devices using DMA
have no idea about DMA position and they can't give DMA controller any
instructions.

>  Yet, I've no good idea to solve problem b) and c).
>
>  I suppose we really need a generic DMA framework, as it seems each DMA
> controller is using its own scheme.
>  For me, a first step in this direction is to break links between devices
> and DMA engines, like it has already be done for esp adapter. Then,
> something good can emerge.
>  You should also notice that I chose _read and _write callbacks for fdc to
> be exactly the same as in esp.

Great! Maybe I should revive some of my generic DMA patches.