DRA74P: Drm ioctl api usage for setting drm master

Ekrem Sahin

Part Number: DRA74P

Hello,

I have a few questions as the following for drm ioctl api:

1.I am trying to create multiple frame buffer on top of a qt application without using qt that means from another executable to show some warning dialogs by using kernel drm ioctl api.First I opened /dev/dri/card0 succesfully but while setting to drm master with ioctl DRM_IOCTL_SET_MASTER I am getting error from kernel that shows drm master is already set.When I debugged the issue, I have observed that dev->master is already true on drm_setmaster_ioctl function and directly exiting from function without setting master on drivers/gpu/drm/drm_auth.c file because of qt application( that run on wayland).For that reason, I am getting permission denied error while calling DRM_IOCTL_MODE_SETCRTC ioctl call.

If I remove qt application and run my development app to draw some shape on screen it is working since at that moment there is no drm master and I can set drm master successfully.So I have observed that there is some ioctl call to share master permission DRM_IOCTL_AUTH_MAGIC but it did not helped me.I can hack the kernel code by removing dev->master check on drm_setmaster_ioctl function from drivers/gpu/drm/drm_auth.c but it is not a good approach.

Could you please give me some direction on the issue to see what I am missing?

2.When I tried to set different size for framebuffer other than our hdmi resolution(1280x720), I do not see any drawing shape on screen with my executable app that I ment on question 1, Could you help me to create different sizes framebuffer by using drm ioctl api?

3.Could you please give me a bit details for drm framebuffer and drm plane.I am a bit confused to use of these functionalities.So I want to show some warning dialogs, some information bar top of qt app on different place on screen, without using qt functions as I mentioned in first question and need to know which one I need to use, framebuffer or plane ? Could you please give me some idea and information ?

Regards

over 5 years ago

0 KB over 5 years ago

TI__Guru*** 126221 points

Hi Ekrem,

As a starting point, could you please provide the SDK version that is being used.

Thanks,

0 Ekrem Sahin over 5 years ago in reply to KB

Prodigy 130 points

Hello KB,

SDK version is : processor sdk 5(yocto release).

Best Regards

0 KB over 5 years ago in reply to Ekrem Sahin

TI__Guru*** 126221 points

Thanks Ekrem,

Apologies for the delay.

How to view the DSS (Display Subsystem), and how it relates to DRM is documented here

The mapping of DRM entities to DSS hardware is roughly as follows:

plane     -> DSS pipeline/overlay
crtc      -> DSS overlay manager
encoder   -> DSS output, encoder, display
connector -> DSS output, encoder, display

From the H/W perspective, if a dedicated DSS pipeline can be made available for the content to be displayed on top of the QT HMI, this would be ideal. From the DRM perspective the pipeline is considered a plane, and framebuffer content would be assigned to the plane. One or more planes can be assigned to a CRTC (overlay).

The zorder of the pipeline/plane, can be adjusted such that it's content is in the foreground (visible), or background on the display.

There is additional information and some examples available both on the link provided above and here.

Regards,

0 Ekrem Sahin over 5 years ago in reply to KB

Prodigy 130 points

Hello Kb,

Thanks for the detailed explanation.So from the examples that you provided and according to my previous investigations, It seems to me I need to set drm master with ioctl DRM_IOCTL_SET_MASTER to set a plane onto QT application and I think it is not possible since wayland is setting the drm master already.

Do you have any idea or example to overcome this problem ?

Best Regards

0 KB over 5 years ago in reply to Ekrem Sahin

TI__Guru*** 126221 points

Hi Ekrem

Unfortunately neither QT nor Wayland provide the ability to access the H/W overlay functionality being discussed (without code modifications). In discussing internally, using the Weston IVI-shell, it may be possible to get the desired overlay.”

See http://software-dl.ti.com/processor-sdk-linux/esd/docs/latest/linux/Foundational_Components/Graphics/Graphics_and_Display.html#using-ivi-shell-feature , for details. Please note that DRA7x is not listed as a supported device on this page.

Regards,

0 Ekrem Sahin over 5 years ago in reply to KB

Prodigy 130 points

Hi KB,

Thanks for the information.So by using the weston ivi shell , is it possible to use drm ioctl api , because I do not want to use any other api ?

And Also, I want to do some generic staffs by using drm ioctl api for the case when a different technology is used other than wayland.

Most of the technology including the wayland and weston uses the drm ioctl api but with the link you provided I have to do some modifications inside wayland or weston

which may cause re-work when wayland is not used.

Do you have any idea to manage this ? Or Am I thinking in a wrong direction ?

Best Regards

0 KB over 5 years ago in reply to Ekrem Sahin

TI__Guru*** 126221 points

Hi Ekrem,

In general, compositors use DRM APIs in the background and the compositor does not let the client/application interface directly with the DRM API code.

If QT/Wayland is a requirement, then using drm ioctl APIs is not an option, unless Weston code is modified. This is not something that TI provides.

A move to any other compositor will likely come with the same restrictions.

Regards,

0 Ekrem Sahin over 5 years ago in reply to KB

Prodigy 130 points

Hi KB,

Thank you really much for the valuable informations. According to the comments from your side , I have to use weston/wayland api to manage my goal and when there is a new compositor

I have to use new api. Do you have a document/example for wayland/weston api use for my goal ?

Best Regards