<adding device tree maintainers to comment>
Hi Maxime
On 1/26/2024 4:45 AM, Maxime Ripard wrote:
On Wed, Jan 17, 2024 at 09:36:20AM -0800, Abhinav Kumar wrote:
Hi Jani and Maxime
On 1/17/2024 2:16 AM, Jani Nikula wrote:
On Wed, 17 Jan 2024, Maxime Ripard <mripard@xxxxxxxxxx> wrote:
Hi,
On Tue, Jan 16, 2024 at 02:22:03PM -0800, Jessica Zhang wrote:
This series introduces a simulated MIPI DSI panel.
Currently, the only way to validate DSI connectors is with a physical
panel. Since obtaining physical panels for all possible DSI configurations
is logistically infeasible, introduce a way for DSI drivers to simulate a
panel.
This will be helpful in catching DSI misconfiguration bugs and catching
performance issues for high FPS panels that might not be easily
obtainable.
For now, the simulated panel driver only supports setting customized
modes via the panel_simlation.mode modparam. Eventually, we would like
to add more customizations (such as configuring DSC, dual DSI, etc.).
I think that it's more complicated than it needs to be.
Both too complicated and not complicated enough! :p
The end goal is to have a framework to be able to validate the display
pipeline with MIPI panels of any resolution , DSC/non-DSC, different MIPI
flags etc.
Historically, QC has been having an in-house framework to validate the
panels in a simulated way as its logistically not possible to procure every
panel from every vendor. This has been working pretty well but its not
upstream yet. So we would like to work with the community to work on a model
which works for everyone and this RFC was initiated with that in mind.
I think the goal was pretty clear. My point was more that there's no
reason it should be driver specific, and having a second path for it
doesn't really exert the actual panel path in the driver. I think a
separate driver would be better.
We can make this generic. That would be great actually. One option could
be to move the modparam we have within the msm to the drm_of.c so that
drm_of_find_panel_or_bridge shall return the sim panel if the modparam
is passed to select a sim panel.
So if we make this a compile time decision whether to use real panel or
sim panel and just enable the appropriate config, we dont need the
modparam and we can implement some policy in the drm_of to first check
if sim panel is available and if not try the real panel then everything
will just happen under-the-hood. But we thought that a modparam based
switching might be convenient if users dont want to recompile the code
to switch but will need to compile both the panels.
There is simulation infrastructure in place in upstream for HDMI/DP in the
form of chamelium based testing in IGT but no such fwk exists for DSI
displays.
Different MIPI panels and resolutions test out not only the DSI controller
but the entire display pipeline as based on resolution, compression and MIPI
mode flags different parts of the pipeline can get exercised.
Why do we need to support (and switch to) both the actual and
"simulated" panel?
As per my discussion on IRC with the panel/bridge maintainers and DT
maintainers, a simulation panel does not qualify for its own devicetree as
its not a real hardware so we needed to come up with a way to have a module
which can be attached to the encoder without its own bindings and
devicetree. Thats what led to this RFC.
I still think it's worth trying, there's plenty of virtual drivers in
the DT already. But even then, DT policies shouldn't dictate general
framework design decisions: we have other ways to probe panels than
using the DT (by loading overlays, registering devices by hand, etc.). I
still think it would be a good idea to try though.
DT option would be great if accepted and will nicely solve the
scalability issue of this as it desperately needs one.
I have absolutely no concerns and would be glad if it will be accepted.
Can the DT maintainers please comment if having a device tree for a
simulation panel would work OR be considered because of the scalability
of the number of panels which can be tried as Maxime wrote.
Wouldn't it be simpler if we had a vkms-like panel that we could either
configure from DT or from debugfs that would just be registered the
usual way and would be the only panel we register?
No, we need to have validate actual hardware pipeline with the simulated
panel. With vkms, actual display pipeline will not be validated. With
incorrect display pipeline misconfigurations arising from different panel
combinations, this can easily be caught with any existing IGT CRC testing.
In addition, all performance related bugs can also be easily caught by
simulating high resolution displays.
That's not what I meant. What I meant was that something like a
user-configurable, generic, panel driver would be a good idea. Just like
vkms (with the debugfs patches) is for a full blown KMS device.
Let me respond for both this question and the one below from you/Jani.
Certainly having user-configurable information is a goal here. The
end-goal is to make everything there in the existing panels such as
below like I wrote:
1) Display resolution with timings (drm_display_mode)
2) Compression/non-compression
3) Command mode/Video mode
4) MIPI mode flags
5) DCS commands for panel enable/disable and other panel sequences
6) Power-up/Power-down sequence for the panel
But, we also have to see what all is feasible today from the DRM fwk
standpoint. There are some limitations about what is boot-time
configurable using bootparams and what is runtime configurable (across a
modeset) using debugfs.
1) Today, everything part of struct mipi_dsi_device needs to be
available at boot time from what I can see as we need that while calling
mipi_dsi_attach(). So for that we went with boot-params.
2) For the list of modes, we can move this to a debugfs like
"populate_modes" which the client using a sim panel can call before
picking a mode and triggering a commit.
But we need to have some default mode and configuration.
This is where I am not totally sure of. On HDMI/DP sinks, we usually go
with a default of 640x480 as that one is guaranteed to be supported
across sinks.
For MIPI displays, we will have to agree on some default configuration then.
So, we can certainly add debugfs to make the runtime params but we need
to start with some default during boot-up and move the others to debugfs.
With vkms, can you pls point us to the debugfs patches you are referring
to? With the current vkms, very little is available which is debugfs
configurable (overlay, writeback and cursor support).
Ofcourse, all these concerns go away if DT option gets accepted.
I get the idea of trying to test DSI code without panels, and looking at
the goals above, I think your vkms suggestion is going to fall short of
those goals.
However, my gut feeling is that creating a simulated panel to catch DSI
misconfiguration etc. is going to be insanely complicated, and this
series doesn't even scratch the surface.
I guess my questions are, what's the scope here really, are those goals
realistic, does more code already exist beyond this skeleton?
This series is only a starting RFC to be able to validate any display mode.
This would have to be extended to be able to customize different pieces of
the panel. Lets talk about the customizable pieces:
1) Display resolution with timings (drm_display_mode)
2) Compression/non-compression
3) Command mode/Video mode
4) MIPI mode flags
5) DCS commands for panel enable/disable and other panel sequences
6) Power-up/Power-down sequence for the panel
Without a physical panel, yes its hard to validate if anything is wrong with
(4) OR (5), the display might not come up at all visually. But from our
experience, thats only a small portion and the real benefit of this
framework will actually be from the validation failures we will catch from
(1) to (4).
This RFC only provides a way to customize (1) at the moment as we wanted to
get some feedback from the community about the best way which will work for
everyone to customize all these parameters.
We are willing to expand this series based on the generic way we agree on to
customize other params.
Yes, debugfs is an option too. But typically MIPI displays need some
parameters configured to attach the panel to the encoder. So perhaps we can
boot the simulation panel with a default resolution passed through command
line and then across a modeset switch (1) to (4).
I think Jani's feeling was that it was going to be super complicated
fairly fast so supporting more features would definitely help to get an
idea of where this is going.
Maxime
