[alsa-devel] ASoC: imx dma tx burst size set to 6 and to 4

[Lambrecht Jürgen]

Hello,

There is an inconsistency in this code:

/sound/soc/imx/imx-ssi.c:         ssi->dma_params_tx.burstsize = 4;
/sound/soc/imx/imx-pcm-dma-mx2.c: ssi->dma_params_tx.burstsize = 6;

Datasheet:
This sets the field TFWM0 in register SFCSR (SSI_SFCSR_TFWM0): the 
number of data words needed to set the empty flag (TFE0). Can be set 
from 1 to 8; FIFO size is 8 words (of 24b). And this is also the DMA 
burst size.

Which is best depends on the application (the higher the more efficient, 
but the more risk for a FIFO underrun). I would take 4.

But I guess it should only be set at 1 place, and what is then the best 
place?

Regards,
Jürgen

details:

/sound/soc/imx/imx-ssi.c: ssi->dma_params_tx.burstsize = 4;
Set in commit
commit 0a93421b6adf8ba127b3eafc4c16e3a14017e2ae
Author: Javier Martin <javier.martin at vista-silicon.com>
Date:   Tue Mar 1 15:02:06 2011 +0100

     ASoC: Fix burstsize and DSP_B format problems in imx-ssi.

     When choosing IMX_DMA flag, burtsizes are set to its default
     value (0) which leads to driver malfunction. Change them to 4.

     DSP_B interface needs additional flag to match DSP_B formats
     as described in several codecs as wm8741 and aic3205.

     Signed-off-by: Javier Martin <javier.martin at vista-silicon.com>
     Acked-by: Liam Girdwood <lrg at slimlogic.co.uk>
     Signed-off-by: Mark Brown <broonie at opensource.wolfsonmicro.com>

Index in diff:
diff --git a/sound/soc/imx/imx-ssi.c b/sound/soc/imx/imx-ssi.c
index 30894ea..bc92ec6 100644

/sound/soc/imx/imx-pcm-dma-mx2.c: ssi->dma_params_tx.burstsize = 6;
Set in commit
commit 2c4cf17a52f04fbe929977252d5b8ab81d2c6e9b
Author: Wolfram Sang <w.sang at pengutronix.de>
Date:   Fri Mar 25 16:51:44 2011 +0100

     ASoC: imx: set watermarks for mx2-dma

     They got accidently removed by f0fba2a (ASoC: multi-component - ASoC
     Multi-Component Support). Reintroduce them and get rid of the
     superfluous defines because the fiq-driver has its own hardcoded 
values.

     Signed-off-by: Wolfram Sang <w.sang at pengutronix.de>
     Acked-by: Liam Girdwood <lrg at ti.com>
     Signed-off-by: Mark Brown <broonie at opensource.wolfsonmicro.com>
     Cc: stable at kernel.org

Index in diff:
diff --git a/sound/soc/imx/imx-pcm-dma-mx2.c 
b/sound/soc/imx/imx-pcm-dma-mx2.c
index 671ef8d..b2ed764 100644
-- 

Jürgen Lambrecht
R&D Associate
Tel: +32 (0)51 303045    Fax: +32 (0)51 310670
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