On Sun, Dec 18, 2016 at 11:06:42PM -0600, Andy Gross wrote:
> On Sun, Dec 18, 2016 at 09:56:02PM +0530, Vinod Koul wrote:
> > On Thu, Dec 15, 2016 at 03:25:52PM +0530, Abhishek Sahu wrote:
> > > The current DMA APIs only support SGL or data in generic format.
> > > The QCA BAM DMA engine data cannot be mapped with already
> > > available APIs due to following reasons.
> > >
> > > 1. The QCA BAM DMA engine uses custom flags which cannot be
> > > mapped with generic DMA engine flags.
> > > 2. Some peripheral driver like QCA QPIC NAND/LCD requires to
> > > set specific flags (Like NWD, EOT) for some of the descriptors
> > > in scatter gather list. The already available mapping APIs take
> > > flags parameter in API itself and there is no support for
> > > passing DMA specific flags for each SGL entry.
> > >
> > > Now this patch adds the support for making the DMA descriptor from
> > > custom data with new DMA mapping function prep_dma_custom_mapping.
> > > The peripheral driver will pass the custom data in this function and
> > > DMA engine driver will form the descriptor according to its own
> > > logic. In future, this API can be used by any other DMA engine
> > > drivers also which are unable to do DMA mapping with already
> > > available API’s.
> > >
> > > Signed-off-by: Abhishek Sahu <absahu@xxxxxxxxxxxxxx>
> > > ---
> > > include/linux/dmaengine.h | 5 +++++
> > > 1 file changed, 5 insertions(+)
> > >
> > > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> > > index cc535a4..6324c1f 100644
> > > --- a/include/linux/dmaengine.h
> > > +++ b/include/linux/dmaengine.h
> > > @@ -692,6 +692,8 @@ struct dma_filter {
> > > * be called after period_len bytes have been transferred.
> > > * @device_prep_interleaved_dma: Transfer expression in a generic way.
> > > * @device_prep_dma_imm_data: DMA's 8 byte immediate data to the dst address
> > > + * @device_prep_dma_custom_mapping: prepares a dma operation from dma driver
> > > + * specific custom data
> > > * @device_config: Pushes a new configuration to a channel, return 0 or an error
> > > * code
> > > * @device_pause: Pauses any transfer happening on a channel. Returns
> > > @@ -783,6 +785,9 @@ struct dma_device {
> > > struct dma_async_tx_descriptor *(*device_prep_dma_imm_data)(
> > > struct dma_chan *chan, dma_addr_t dst, u64 data,
> > > unsigned long flags);
> > > + struct dma_async_tx_descriptor *(*device_prep_dma_custom_mapping)(
> > > + struct dma_chan *chan, void *data,
> > > + unsigned long flags);
> >
> > This needs a discussion. Why do you need to add a new API for framework.
> >
> > What are NWD and EOT flags, cna you details out the flags?
>
> These are the notify when done and end of transaction flags. I believe the last
> time we talked about this, we (Vinod and I) agreed to just expose a QCOM only interface to set
> the special transaction flags. You'd then have to have some other API to fixup
> the descriptor with the right qcom flags.
Okay, do you have pointer on that one, will avoid asking the same questions
again.
> Ahbishek, correct me where i am wrong on the following:
> So two main differences between a normal descriptor and a command descriptor:
> 1) size of the descriptor
> 2) the flag setting
> 3) data sent in is a modified scatter gather that includes flags , vs a normal
> scatter gather
>
> So the CMD descriptors in a given sgl can all have varying flags set? I'd assume
> they all have CMD flag set. Do the current users of the command descriptors
> coalesce all of their requests into a big list?
>
> So a couple of thoughts on how to deal with this:
>
> 1) Define a virtual channel for the command descriptors vs a normal DMA
> transaction. This lets you use the same hardware channel, but lets you discern
> which descriptor format you need to use. The only issue I see with this is the
> required change in device tree binding to target the right type of channel (cmd
> vs normal).
Or mark the descriptor is cmd and write accordingly...
>
> 2) Provide an API to set flags for the descriptor on a whole descriptor basis.
>
> 3) If you have a set of transactions described by an sgl that has disparate use
> of flags, you split the list and use a separate transaction. In other words, we
> need to enforce that the flag set API will be applied to all descriptors
> described by an sgl. This means that the whole transaction may be comprised of
> multiple async TX descriptors.
--
~Vinod
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