On 01/15/2014 03:48 PM, Anssi Hannula wrote: > 15.01.2014 13:27, Jyri Sarha kirjoitti: >> On 12/31/2013 03:25 PM, Mark Brown wrote: >>> On Fri, Dec 20, 2013 at 12:39:38PM +0200, Jyri Sarha wrote: >>>> support. The only supported sample format is SNDRV_PCM_FORMAT_S32_LE. >>>> The 8 least significant bits are ignored. >>> >>> Where does this constraint come from? >>> >> >> From driver/gpu/drm/i2c/tda998x_drv.c. The driver configures CTS_N >> register statically to a value that works only with 4 byte samples. >> According to my tests it is possible to support 3 and 2 byte samples too >> by changing the CTS_N register value, but I am not sure if the >> configuration can be changed on the fly. My data sheet of the nxp chip >> is very vague about the register definitions, but I suppose the register >> configures some clock divider on the chip. HDMI supports only upto 24bit >> audio and the data sheet states that any extraneous least significant >> bits are ignored. > > That sounds strange, CTS/N values only depend on audio sample rate and > TMDS/video clock, not on the audio format or the size of samples (HDMI > spec sec 7.2 - Audio Sample Clock Capture and Regeneration). > > Sure there isn't anything more going on (like the used HDMI sink being > more tolerant to wrong CTS/N with 4-byte samples, or more likely > something else I can't immediately think of)? >
On theoretical level I am not really sure about anything, because have not been able to get my hands on proper NXP TDA19988 documentation. However, while playing around with my Beaglebone-Black I have have found out in practice that by changing CTS_N register's (page 0x11 reg 0x0c) K_SEL bits (bit 2 to 0)[1] I can get 2, 3 and 4 byte samples to work consistently by setting: K_SEL = 1 for SNDRV_PCM_FORMAT_S16_LE K_SEL = 2 for SNDRV_PCM_FORMAT_S24_3LE K_SEL = 3 for SNDRV_PCM_FORMAT_S32_LE Because I do not really know what is going on, I did not want to suggest any changes to the driver and just use the format that works with the current driver version. The HDMI sinks I have been using are a Toshiba 22B2LF1G and Thomson 42E90NF32 televisions. About those I just know that they both behave the same way. Best regards, Jyri [1] The closest data sheet that has any description about the chip registers I have found is this: http://media.digikey.com/pdf/Data%20Sheets/NXP%20PDFs/TDA9983B.pdf
