linux-kernel - Re: [PATCHv2] DMAEngine: Define generic transfer request api

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Message-ID: <CAJe_Zhd5d7XeuVJpuyNYBmhwBkX_dgi+nngftCO9C589cF1Yqg@mail.gmail.com>
Date:	Fri, 16 Sep 2011 18:00:31 +0530
From:	Jassi Brar <jaswinder.singh@...aro.org>
To:	Vinod Koul <vinod.koul@...el.com>
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 16 September 2011 14:37, Vinod Koul <vinod.koul@...el.com> wrote:
> On Thu, 2011-09-15 at 13:16 +0530, Jassi Brar 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.


>> +/**
>> + * 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.
>> + * @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.
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