linux-kernel - Re: [PATCH v2 0/2] Add Qualcomm MSM ADM DMAEngine driver

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Date:	Fri, 20 Jan 2012 19:01:27 +0530
From:	Vinod Koul <vinod.koul@...el.com>
To:	Ravi Kumar V <kumarrav@...eaurora.org>
Cc:	dan.j.williams@...el.com, arnd@...db.de,
	linux-arch@...r.kernel.org, davidb@...eaurora.org,
	dwalker@...o99.com, bryanh@...eaurora.org, linux@....linux.org.uk,
	tsoni@...lcomm.com, johlstei@...lcomm.com,
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 0/2] Add Qualcomm MSM ADM DMAEngine driver

On Fri, 2012-01-20 at 18:00 +0530, Ravi Kumar V wrote:
> On 1/17/2012 7:15 PM, Vinod Koul wrote:
> > On Fri, 2012-01-06 at 18:17 +0530, Ravi Kumar V wrote:
> > <sorry for delayed review, was on vacation and now traveling>
> >>
> >> As our ADM Scatter-gather hardware needs
> >> -32-bit command configuration parameter
> >>   apart from
> >> -32-bit source address
> >> -32-bit destination address
> >> -16-bit length
> >>
> >> So,we have added new parameter in struct scatterlist to support xfer
> >> descriptor
> >> specific private data, and for supporting ADM Box mode DMA we added
> >> new
> >> API and data structure.
> > what do you mean by "ADM Box mode"?
> >
> 
> ADM Box mode is a interleaved type of DMA where data from rows of equal 
> length and equal distance(bytes) between each other are transferred to 
> similar pattern of rows.
> Each row length and distance between each row in destination pattern may 
> not be equal to source pattern.
> Distance between beginning of any two rows are always greater than row 
> length.
> Example:
> If 4 rows of 16 bytes each are arranged such that distance between 
> beginning of any two rows are 32 bytes.
> Now they can be transferred using BOX mode to destination pattern 
> arranged in 2 rows of 32 bytes each and distance between them can be any 
> lets say 128 bytes.
> 
> Source pattern:
> 4 data rows starts address 0th byte.
> 
> 0-----16-bytes-data-----15
> 16    16 bytes void     31
> 32---------data---------47
> 48         void         63
> 64---------data---------79
> 80         void         95
> 96---------data--------111
> 
> Transferred to destination
> Destination pattern:
> 2 rows
> 0----------32-bytes-data----------31
> 32         96 bytes void         127
> 128-------------data-------------159
> 
Sounds like you should be using interleaved API

Please see this and read the patch history, which has nice details about
this

/**
 * struct dma_interleaved_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.
 * @dir: Specifies the type of Source and Destination.
 * @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.
 * @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 dma_interleaved_template {
        dma_addr_t src_start;
        dma_addr_t dst_start;
        enum dma_transfer_direction dir;
        bool src_inc;
        bool dst_inc;
        bool src_sgl;
        bool dst_sgl;
        size_t numf;
        size_t frame_size;
        struct data_chunk sgl[0];
};
using the interleaved API:
        struct dma_async_tx_descriptor *(*device_prep_interleaved_dma)(
                struct dma_chan *chan, struct dma_interleaved_template *xt,
                unsigned long flags);


-- 
~Vinod

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