Re: [linux-sunxi] Re: [PATCH RESEND v2 08/12] dt-bindings: add binding for generic eDP panel

On Mon, Feb 4, 2019 at 8:39 AM Rob Herring [off-list ref] wrote:

On Mon, Feb 4, 2019 at 10:11 AM Vasily Khoruzhick [off-list ref] wrote:

quoted

On Mon, Feb 4, 2019 at 12:24 AM Thierry Reding [off-list ref] wrote:

quoted

quoted

Pinebook used several 768p panels that have slightly different timings
and recent batch uses 1080p panel.

What panel descriptor should I use as fallback?

You don't use panel descriptors as fallback. The simple-panel driver
will bind to a panel device and use the corresponding descriptor. If
your device tree contains the correct information, the descriptor is
correct for the panel you have.

In other words you need to ensure that you have the correct panel in
device tree for the board that you're using. This is exactly the same
thing as for other devices.

One way to to this is to have separate device trees for each variant
of the board that you want to support. Another variant may be to have
a common device tree and then have some early firmware update the DTB
with the correct panel information.

That defeats the purpose of using eDP panels. Panel can identify
itself and report what timings it supports.

If you are confident that this works for all panels, then the firmware
can identify the right panel and update the DTB with the correct
information. If this doesn't work in the firmware, then it is not
going to work in the kernel either and you are SOL without specific
panel information in the DT.

"firmware" is u-boot and on this platform it sits on the same physical
media as OS (it's either microsd or eMMC).

I guess u-boot can fill in timings for kernel, but I don't see much
point in it. If u-boot can't read EDID then same is true
for kernel.

quoted

If we use separate DTBs then users will have to figure out what panel
is installed in their hardware and use appropriate software image -
that's something I'd like to avoid.

I think Thierry meant either way this is a firmware problem. If you
have a SKU per device and panel type, then the firmware just picks a
dtb among a set.

Unfortunately it's one SKU per multiple panels.

Rob

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