On 2019-08-14 13:14, Robert Chiras wrote:

Hi Stefan,
On Mi, 2019-08-14 at 13:03 +0200, Stefan Agner wrote:

quoted

On 2019-08-14 12:48, Robert Chiras wrote:

quoted

Add new optional property 'max-res', to limit the maximum supported
resolution by the MXSFB_DRM driver.

I would also mention the reason why we need this.

I guess this needs a vendor prefix as well (fsl,max-res). I also
would
like to have the ack of the device tree folks here.

Rob Herring also aked be about this, and I'll copy here the reply, with
explanations:

Indeed, this limitation is actually due to bandwidth limitation, but
the problem is that this limitation comes on i.MX8M (known as mScale
850D), where the memory bandwidth cannot support: GPU/VPU workload in
the same time with both DCSS driving 4k@60 and eLCDIF driving 1080p@60.
Since eLCDIF is a secondary display we though to add the posibility to
limit it's bandwidth by limiting the resolution.
If you say that more details are needed, I can add them in the
description.

Oh sorry I missed that.

Rob Herring also wrote:

I suppose what you are after is bandwidth limits? IIRC, there's already 
some bindings expressing such limits. Also, wouldn't you need to account 
for bpp and using the 2nd plane (IIRC that there is one).

I guess the binding he refers to is max-memory-bandwidth, which is used
in multiple driver already. It makes sense to reuse this property
instead of inventing a new set of property which is also not taking bpp
into account...

The pl111 driver implements this property, it should be fairly easy to
adopt that code.

--
Stefan

quoted

--
Stefan

quoted

Signed-off-by: Robert Chiras <robert.chiras@nxp.com>
---
 Documentation/devicetree/bindings/display/mxsfb.txt | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/devicetree/bindings/display/mxsfb.txt

b/Documentation/devicetree/bindings/display/mxsfb.txt
index 472e1ea..55e22ed 100644

--- a/Documentation/devicetree/bindings/display/mxsfb.txt
+++ b/Documentation/devicetree/bindings/display/mxsfb.txt

@@ -17,6 +17,12 @@ Required properties:

 Required sub-nodes:
   - port: The connection to an encoder chip.

+Optional properties:
+- max-res:   an array with a maximum of two integers, representing
the
+             maximum supported resolution, in the form of
+             <maxX>, <maxY>; if one of the item is <0>, the
default
+             driver-defined maximum resolution for that axis is
used
+
 Example:

      lcdif1: display-controller@2220000 {

Thanks,
Robert

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