[PATCH] drm: dw_hdmi: Gate audio sampler clock from the enablement functions

Russell King - ARM Linux linux at armlinux.org.uk
Mon Mar 13 02:36:30 PDT 2017

On Mon, Mar 13, 2017 at 10:27:08AM +0100, Neil Armstrong wrote:
> On 03/10/2017 10:35 AM, Romain Perier wrote:
> > Currently, the audio sampler clock is enabled from dw_hdmi_setup() at
> > step E. and is kept enabled for later use. This clock should be enabled
> > and disabled along with the actual audio stream and not always on (that
> > is bad for PM). Futhermore, this might cause sound glitches with some
> > HDMI devices, as the CTS+N is forced to zero when the stream is disabled
> > while the audio clock is still running.
> > 
> > This commit adds a parameter to hdmi_audio_enable_clk() that controls
> > when the audio sample clock must be enabled or disabled. Then, it moves
> > the call to this function into dw_hdmi_audio_enable() and
> > dw_hdmi_audio_disable().
> > 
> > Signed-off-by: Romain Perier <romain.perier at collabora.com>
> > ---
> >  drivers/gpu/drm/bridge/dw-hdmi.c | 15 +++++++++------
> >  1 file changed, 9 insertions(+), 6 deletions(-)
> > 
> Hi Romain, Russell, Jose,
> This is a little out of scope, but I was wondering why the CTS calculation
> was not left in AUTO mode in the dw-hdmi driver ?

There is no indication in the iMX6 manuals that the iMX6 supports
automatic CTS calculation.  Bits 7:4 of the AUD_CTS3 register are
marked as "reserved".

We're reliant on the information in the iMX6 manuals as we don't have
access to Synopsis' databooks for these parts (I understand you have
to be a customer to have access to that.)

RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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