On 05/16/2016 05:31 PM, Laurent Pinchart wrote: > Hi Archit, > > On Friday 22 Apr 2016 11:10:18 Archit Taneja wrote: >> On 04/22/2016 04:02 AM, Laurent Pinchart wrote: >>> On Wednesday 09 Mar 2016 16:27:18 Archit Taneja wrote: >>>> Add description of ADV7533. Add the required and optional properties that >>>> are specific to it. >>>> >>>> Cc: devicetree at vger.kernel.org >>>> Cc: Rob Herring <robh at kernel.org> >>>> >>>> Signed-off-by: Archit Taneja <architt at codeaurora.org> >>>> --- >>>> >>>> .../bindings/display/bridge/adi,adv7511.txt | 25 ++++++++++++----- >>>> 1 file changed, 20 insertions(+), 5 deletions(-) >>>> >>>> diff --git >>>> a/Documentation/devicetree/bindings/display/bridge/adi,adv7511.txt >>>> b/Documentation/devicetree/bindings/display/bridge/adi,adv7511.txt index >>>> 96c25ee..420da5a 100644 >>>> --- a/Documentation/devicetree/bindings/display/bridge/adi,adv7511.txt >>>> +++ b/Documentation/devicetree/bindings/display/bridge/adi,adv7511.txt > > [snip] > >>>> +- adi,disable-timing-generator: Only for ADV7533. Disables the internal >>>> timing >>>> + generator. The chip will rely on the sync signals in the DSI data >>>> lanes, >>>> + rather than generate its own timings for HDMI output. >>> >>> Isn't that something that should be selectable at runtime ? >> >> The timing generator can be enabled/disabled at runtime. Although, we >> don't have a way to tell the driver whether we want to keep it enabled >> or not. >> >> It's a hardware feature that works well on most platforms, but not on >> all. In particular, it works well on DB410c, but causes issues with >> the Hikey 96 board. The DSI host on Hikey has different clock sources >> that generate the display controller's pixel clock and DSI byte clock, >> whereas the Qualcomm SoC uses the same source. My guess is that the >> ADV7533's timing generator doesn't like it when the pixel data and >> clock are out of phase or something. >> >> Since it is a hardware feature which needs tweaking, I thought it >> qualified as a DT property. > > The fact that a hardware generator is present is certainly describes the > hardware, but I'm not sure whether to enable it or not also qualifies as a > hardware feature. > > Are there use cases for using the timing generator conditionally on a given > board ? As you implement support for disabling it, I assume it's not > mandatory. What feature(s) do we lose if we keep it disabled ? >
The spec says it's recommended to use the internal timing generator. In the case of db410c, I observe an unstable output/flicker for certain modes if I don't enable it. In the case of hikey platform, it's the other way round. Xinliang, could you describe the problems you face when the timing generator is enabled? Thanks, Archit -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation
