Message-ID: <1316402638.21359.16.camel@vkoul-udesk3>
Date:	Mon, 19 Sep 2011 08:53:58 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Jassi Brar <jaswinder.singh@...aro.org>
Cc:	dan.j.williams@...el.com, linux-kernel@...r.kernel.org,
	rmk+kernel@....linux.org.uk, 21cnbao@...il.com
Subject: Re: [PATCHv2] DMAEngine: Define generic transfer request api

On Fri, 2011-09-16 at 23:21 +0530, Jassi Brar wrote:
> On 16 September 2011 22:36, Vinod Koul <vinod.koul@...el.com> wrote:
> >> >> Define a new api that could be used for doing fancy data transfers
> >> >> like interleaved to contiguous copy and vice-versa.
> >> > Then this is a very specific type of transfer this API supports, so the
> >> > name generic_xxx is not apt!
> >>
> >> Currently it doesn't support every operation, perhaps there will be an
> >> operation that couldn't ever be merged into this.
> >> But it does support interleaved(async and slave), memcpy, memset, dma_sg,
> >> slave_sg, and cyclic.
> >> Please feel free to suggest a better name.
> > ATM, this api is for interleaved like dma operation. so
> > prep_interleaved_dma may be better suited.
> Well, ok I can live with that.
> 
> > Let the generalization be discussed separately...
> As you wish.
> 
> >> >> +/**
> >> >> + * Generic Transfer Request
> >> >> + * ------------------------
> >> >> + * A chunk is collection of contiguous bytes to be transfered.
> >> >> + * The gap(in bytes) between two chunks is called inter-chunk-gap(ICG).
> >> >> + * ICGs may or maynot change between chunks.
> >> >> + * A FRAME is the smallest series of contiguous {chunk,icg} pairs,
> >> >> + *  that when repeated an integral number of times, specifies the transfer.
> >> >> + * A transfer template is specification of a Frame, the number of times
> >> >> + *  it is to be repeated and other per-transfer attributes.
> >> >> + *
> >> >> + * Practically, a client driver would have ready a template for each
> >> >> + *  type of transfer it is going to need during its lifetime and
> >> >> + *  set only 'src_start' and 'dst_start' before submitting the requests.
> >> >> + *
> >> >> + *
> >> >> + *  |      Frame-1        |       Frame-2       | ~ |       Frame-'numf'  |
> >> >> + *  |====....==.===...=...|====....==.===...=...| ~ |====....==.===...=...|
> >> >> + *
> >> >> + *    ==  Chunk size
> >> >> + *    ... ICG
> >> >> + */
> >> >> +
> >> >> +/**
> >> >> + * struct data_chunk - Element of scatter-gather list that makes a frame.
> >> >> + * @size: Number of bytes to read from source.
> >> >> + *     size_dst := fn(op, size_src), so doesn't mean much for destination.
> >> >> + * @icg: Number of bytes to jump after last src/dst address of this
> >> >> + *    chunk and before first src/dst address for next chunk.
> >> >> + *    Ignored for dst(assumed 0), if dst_inc is true and dst_sgl is false.
> >> >> + *    Ignored for src(assumed 0), if src_inc is true and src_sgl is false.
> >> >> + */
> >> >> +struct data_chunk {
> >> >> +     size_t size;
> >> >> +     size_t icg;
> >> >> +};
> >> >> +
> >> >> +/**
> >> >> + * struct dmaxfer_template - Template to convey DMAC the transfer pattern
> >> >> + *    and attributes.
> >> >> + * @src_start: Bus address of source for the first chunk.
> >> >> + * @dst_start: Bus address of destination for the first chunk.
> >> >> + * @src_inc: If the source address increments after reading from it.
> >> >> + * @dst_inc: If the destination address increments after writing to it.
> >> >> + * @src_sgl: If the 'icg' of sgl[] applies to Source (scattered read).
> >> >> + *           Otherwise, source is read contiguously (icg ignored).
> >> >> + *           Ignored if src_inc is false.
> >> >> + * @dst_sgl: If the 'icg' of sgl[] applies to Destination (scattered write).
> >> >> + *           Otherwise, destination is filled contiguously (icg ignored).
> >> >> + *           Ignored if dst_inc is false.
> >> >> + * @frm_irq: If the client expects DMAC driver to do callback after each frame.
This should be specified in the callback field in descriptor..

> >> >> + * @numf: Number of frames in this template.
> >> >> + * @frame_size: Number of chunks in a frame i.e, size of sgl[].
> >> >> + * @sgl: Array of {chunk,icg} pairs that make up a frame.
> >> >> + */
> >> >> +struct dmaxfer_template {
> >> >> +     dma_addr_t src_start;
> >> >> +     dma_addr_t dst_start;
> >> >> +     bool src_inc;
> >> >> +     bool dst_inc;
> >> >> +     bool src_sgl;
> >> >> +     bool dst_sgl;
> >> >> +     bool frm_irq;
> >> >> +     size_t numf;
> >> >> +     size_t frame_size;
> >> >> +     struct data_chunk sgl[0];
> >> >> +};
> >> > This kind of transfer can be either slave (audio interleaved) based or
> >> > mem-to-mem (extracting still image from a buffer),
> >> > How do you propose the dmac know about this is unclear to me
> >>
> >> Every 'prepare' callback already passes the channel chosen for the transfer.
> >> And the DMAC driver already knows if that channel is SLAVE capable or not.
> > How about above params, you should add they may/may not be valid
> > depending upon the mode.
> If you look at the documentation above the 'struct dmaxfer_template', I have
> already mentioned what params are ignored/invalid when.
> Or is there something else you want mentioned ?
How would dmacs decodes these addresses for slave transfers, some maybe
valid some not based on the direction... a note would be good :)

-- 
~Vinod

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