[PATCH 4/4] drm/bridge: dw-hdmi: add cec driver

On 06/02/17 11:15, Russell King - ARM Linux wrote:

On Fri, Jun 02, 2017 at 06:02:28AM +0100, Jose Abreu wrote:

quoted

You should check that CEC is: not in standy, acknowledges
broadcast messages, signal free time is 5bit period, and not lost
arbitration, which basically means CEC_CTRL must be 0x2 and
IH_CEC_STAT0 must not have ARB_LOST set.

If ARB_LOST is set, that will trigger an interrupt, and the interrupt
handler will clear the bit.  So all the time that the interrupt handler
is present, ARB_LOST should be clear whenever we try to send a message.

When we enable the CEC interface, we zero the CEC_CTRL register, which
takes the controller out of standby, and initialises the command
register.

Bits 2:1 select the signal free time, and there's no requirement
specified to require them to be set to '01' before writing the
message - in fact, it's legal for them to be set to other values,
particularly when retrying, which is something I've missed.

     2-1             Frame Type bit
  FRAME_TYP
                     00    Signal Free Time = 3-bit periods. Previous
			   attempt to send frame is unsuccessful.
                     01    Signal Free Time = 5-bit periods. New initiator
			   wants to send a frame.
                     10    Signal Free Time = 7-bit periods. Present
			   initiator wants to send another frame
			   immediately after its previous frame. (spec
			   CEC 9.1)
                     11    Illegal value. If software write this value,
			   hardware will set the value to the default 2'b01.

The 'signal_free_time' argument of adap_transmit will have the recommended
signal free time. You can test against the CEC_SIGNAL_FREE_TIME_* defines
from media/cec.h. You probably saw this already, but just in case you missed
this...

Regards,

	Hans