Hi Yegor,
On Fri, Mar 01, 2013 at 16:23:53, Yegor Yefremov wrote:
I've solved the problem with DIT/SPDIF mode (see the issue description here: http://e2e.ti.com/support/arm/sitara_arm/f/791/p/247447/870030.aspx).
In davinci_mcasp_hw_params() the DIT or I2S params will be set in the beginning. DIT mode configures the DAVINCI_MCASP_TXMASK_REG and DAVINCI_MCASP_TXFMT_REG.
And here comes the problem:
at the end of davinci_mcasp_hw_params() the davinci_config_channel_size() will touch the same registers again and thus overwrite the settings necessary for DIT. After I commented this routine I got the sound over S/PDIF and sii9022a HDMI transmitter and I could see the proper bits appearing on my oscilloscope.
What were the best way to solve this problem?
- execute davinci_config_channel_size() only if not in DIT mode?
- for DIT only change the DAVINCI_MCASP_TXMASK_REG according to channel width?
- execute
if (dev->op_mode == DAVINCI_MCASP_DIT_MODE) davinci_hw_dit_param(dev); else davinci_hw_param(dev, substream->stream);
after davinci_config_channel_size()
AFAIK DIT mode was working on Davinci platforms some time back. Since AM335x has the same hardware block I was surprised to see this bug report. Not having a setup handy to test out DIT related changes, I looked at the commits on the mcasp file to figure out what happened. I suspect one of the recent patches which added 24bit support inadvertently broke the DIT support. Would it be possible for you to do a git-bisect to find out what change it was? It would be good to reference that change in the final patch.
Coming to the 3 options that you have listed I would suggest going with #1. DIT mode requires the configuration to be 32 bit slot with rotation set to 24 but looks like the current implementation of davinci_config_channel_size() doesn't handle this scenario very well. I think the driver needs a bit of rework to ensure Tx and Rx paths don't end up overwriting the configuration but that needs to be taken up separately.
#2 looks to more of a workaround and IMO #3 places an implicit dependency on the call order without solving the overwrite issue that you hit.
Regards, Vaibhav