Re: [PATCH 1/2] McBSP DMA support for 34xx

["shekhar, chandra" <x0044955@ti.com>]

----- Original Message ----- 
From: "Jarkko Nikula" <jarkko.nikula@nokia.com>
To: "ext chandra shekhar" <x0044955@ti.com>
Cc: <linux-omap@vger.kernel.org>
Sent: Thursday, August 28, 2008 4:22 PM
Subject: Re: [PATCH 1/2] McBSP DMA support for 34xx


> On Thu, 28 Aug 2008 13:56:00 +0530 (IST)
> "ext chandra shekhar" <x0044955@ti.com> wrote:
>
>> This patch supports DMA chaining mode and one time configuration for
>> entire transfer to improve performance.
>> Signed-off-by: chandra shekhar <x0044955@ti.com>
>> ---
>>  arch/arm/mach-omap2/mcbsp.c       |  702 ++++++++++++++++++++++++++++
>> +++++++++- arch/arm/plat-omap/mcbsp.c        |   19 -
>>  include/asm-arm/arch-omap/mcbsp.h |  127 +++++-
>>  3 files changed, 811 insertions(+), 37 deletions(-)
>>
> Hi
>
> What's the expected use case for DMA chaining mode or existing driver
> which would get improved performance? There should have some reason why
> this amount of new lines should be added.

current McBSP ( arch/arm/plat-omap/mcbsp.c) code request and releases dma 
channel for each transfer .
so there is latency involved. Chaining help with smooth audio play because we 
can enque the buffer
while another transfer is ongoing.

>
> Also ideally this should cover also OMAP1's from 16xx onward since they
> can link DMA channels together as well?

Current code might even work for 16xx and later versions for 16 bit data. ( or 
can be extended to work on 16xx and later versions)
but i dont have board or TRM to check for any changes in DMA subsytem or McBSP. 
better to play safe.

2430 onwards McBSP dxr/drr is 32 bits, which allows 24 bit mono/stereo transfer 
easily. if we had to have 16 bit dxr1,2/drr1,2
then we will have to perform the manipulation on data for 24 bit ops. we will 
have to consider all the options before extending it to 16xx.

>
>
> Jarkko
>