Messages in this thread | | | Subject | RE: [PATCHv4] DMAEngine: Define interleaved transfer request api | Date | Fri, 14 Oct 2011 10:50:41 -0700 | From | "Bounine, Alexandre" <> |
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On Tue, Oct 11, 2011 at 12:45 PM, Williams, Dan J <dan.j.williams@intel.com> wrote:
> Subject: Re: [PATCHv4] DMAEngine: Define interleaved transfer request > api > > [ Adding Alexandre ] > > On Fri, Oct 7, 2011 at 4:27 AM, Jassi Brar <jaswinder.singh@linaro.org> > wrote: > > On 7 October 2011 11:15, Vinod Koul <vinod.koul@intel.com> wrote: > > > >> Thru this patch Jassi gave a very good try at merging DMA_SLAVE and > >> memcpy, but more we debate this, I am still not convinced about > merging > >> memcpy and DMA_SLAVE yet. > >> > > Nobody is merging memcpy and DMA_SLAVE right away. > > The api's primary purpose is to support interleave transfers. > > Possibility to merge other prepares into this is a side-effect. > > > >> I would still argue that if we split this on same lines as current > >> mechanism, we have clean way to convey all details for both cases. > >> > > Do you mean to have separate interleaved transfer apis for Slave > > and Mem->Mem ? Please clarify. > > > > This is a tangent, but it would be nice if this API extension also > covered the needs of the incoming RapidIO case which wants to specify > new device context information per operation (and not once at > configuration time, like slave case). Would it be enough if the > transfer template included a (struct device *context) member at the > end? Most dma users could ignore it, but RapidIO could use it to do > something like: > > struct rio_dev *rdev = container_of(context, typeof(*rdev), device); > > That might not be enough, but I'm concerned that making the context a > (void *) is too flexible. I'd rather have something like this than > acquiring a lock in rio_dma_prep_slave_sg() and holding it over > ->prep(). The alternative is to extend device_prep_slave_sg to take > an extra parameter, but that impacts all other slave implementations > with a dead parameter. >
Having context limited to the device structure will not be enough for RapidIO because of 66-bit target address (dma_addr_t will not work here). Probably that range is out of practical use at this moment but it is defined by RIO specification and I would prefer to deal with it now instead of postponing it for future. Passing context using (void *) will solve this.
Alex.
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