Re: [PATCH v3 2/2] DMAEngine: Add DMAEngine driver based on old MSM DMA APIs

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On 3/15/2012 1:49 AM, David Brown wrote:
On Wed, Mar 14, 2012 at 08:05:53AM -0700, Daniel Walker wrote:
On Tue, Mar 13, 2012 at 06:16:39PM +0530, Ravi Kumar V wrote:
On 3/13/2012 1:44 AM, Daniel Walker wrote:
On Mon, Mar 12, 2012 at 04:02:44PM +0530, Ravi Kumar V wrote:
Add DMAEngine based driver using the old MSM DMA APIs internally.

What do you mean by this?

There is a MSM DMA driver in arch/arm/mach-msm/ which is not in
dmaengine framework standards, but that driver is been used by
client drivers nand, eMMC and serial drivers. Now if we implement
the whole dma driver using dmaengine framework then nand, eMMC like
drivers will be failed as they are using old dma driver API's, so
instead of implementing new driver from scratch we are keeping the
old dma API's as it is and using those API's in new dmaengine
framework.So that we can convert clients drivers to use dma engine

Did you investigate converting the drivers (nand, eMMC, serialied ) ? It
seems like there would be a 1:1 mapping between the API's , so it might
only be a find->replace operation.

Only at a very superficial level--they both do DMA.  The ADM driver
wants its scatterlists constructed manually by the caller (in DMA-able
memory) and just the pointer handed over.  The drivers will have to be
converted to use the abstracted scatterlists that dmaengine wants.
Drivers like msm_sdcc are currently fairly intimitely tied to flow
that is specific to ADM.  The msm_sdcc driver also needs use of the
ADM's "box" mode, which has to be made to work with DMAEngine as well.

Providing both APIs is really the only practical way to get this in
without having to rewrite several other drivers.

The nand driver (which doesn't seem to have made it in yet, is much worse.  About half of the
code is constructing ADM specific command blocks.  I'm not even sure
it will be practical to even migrate that driver to DMAEngine, since
the nand controller hardware is so intimately tied to the functioning
of the ADM.


Yes i have tried to convert these drivers, but mostly we need to add DMAEngine stuff like requesting channel, creating the descriptors, passing these descriptors to channel etc which are different from old implementation.So we have choose this path not to disturb the existing drivers while converting a driver.

Ravi Kumar V
Sent by a consultant of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

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