Hi Laurent,
Thanks for the feedback.
Subject: Re: [PATCH 1/2] dt-bindings: drm: bridge: adi,adv7533: Document adi,disable-lanes-override property
Hi Biju,
Thank you for the patch.
On Wed, Mar 09, 2022 at 03:11:08PM +0000, Biju Das wrote:
On Renesas RZ/{G2L,V2L} platforms changing the lanes from 4 to 3 at lower frequencies causes display instability. On such platforms, it is better to avoid switching lanes from 4 to 3 as it needs different set of PLL parameter constraints to make the display stable with 3 lanes.
Is this because the PLL calculation code doesn't work properly, or because the hardware can't support this ?
PLL Calculation is correct, that is the reason it works for all resolution with 4 lanes. There are 2 clocks generated by PLL5 which is connected to a mux with clock sources, namely 'FOUTPOSTDIV' and 'FOUT1PH0'
This Mux is connected to DSI dividers.
'FOUTPOSTDIV' should be selected if (PLL_INPUT_FREQ/VCLK) is odd and 'FOUT1PH0' should be selected if it is even.
The PLL calculation makes use of even selection('FOUT1PH0') and video works for all frequencies with 4 lanes.
With 'FOUT1PH0' as clock source, if I switch to 3 lanes for lanes it doesn't work. But it work with 4lanes on all frequencies.
HW can support 3 lanes, if I set parameter to make (PLL_INPUT_FREQ/VCLK) odd and select 'FOUTPOSTDIV' as clk source to DSI divider.
I am not sure about the rational behind the constraint to Switch to 3 lanes for lower frequency for this ADV7535 chip, as on our platform it can work with 4lanes on all frequencies.
Cheers, Biju
This patch introduces 'adi,disable-lanes-override' property to disable lane switching at lower frequencies.
Signed-off-by: Biju Das biju.das.jz@bp.renesas.com Reviewed-by: Lad Prabhakar prabhakar.mahadev-lad.rj@bp.renesas.com
.../devicetree/bindings/display/bridge/adi,adv7533.yaml | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/Documentation/devicetree/bindings/display/bridge/adi,adv7533.yaml b/Documentation/devicetree/bindings/display/bridge/adi,adv7533.yaml index f36209137c8a..2dc378039d21 100644
a/Documentation/devicetree/bindings/display/bridge/adi,adv7533.yaml +++ b/Documentation/devicetree/bindings/display/bridge/adi,adv7533.yam +++ l @@ -84,6 +84,11 @@ properties: timings for HDMI output. type: boolean
- adi,disable-lanes-override:
- description:
Disables the overriding lanes at lower frequencies.- type: boolean
- adi,dsi-lanes: description: Number of DSI data lanes connected to the DSI host. $ref: /schemas/types.yaml#/definitions/uint32
-- Regards,
Laurent Pinchart