Hello Thomas,
On 3/30/22 12:32, Thomas Zimmermann wrote:
Hi
[snip]
-obj-$(CONFIG_DRM_DP_HELPER) += drm_dp_helper.o +obj-$(CONFIG_DRM_DISPLAY_HELPER) += drm_display_helper.o
The drm_dp_helper.ko module has some parameters and this change will break existing kernel cmdline that are using it:
$ modinfo drivers/gpu/drm/dp/drm_dp_helper.ko | grep parm | cut -d : -f2 drm_dp_cec_unregister_delay dp_aux_i2c_speed_khz dp_aux_i2c_transfer_size
I don't know whether those are considered a kernel ABI or not though, and some already changed when the DP helpers were moved from drm_kms_helper.ko
Good point. I'll mention it in the commit message andcheck the documentation as well.
At least, no one complained when these functions moved from kms helpers into dp helpers. Moving them again is unfortunate, but I hope that the new library will stick.
I was just pointing out because honestly I didn't know what was the kernel policy around changing kernel command line parameters. It seems that isn't documented anywhere.
But since no one complained when these were moved from drm_kms_helper.ko and the current drm_dp_helper.ko is so recent, I would say that's fine.
If you re-spin feel free to add,
Reviewed-by: Javier Martinez Canillas javierm@redhat.com
I somehow expected that HDMI, HDCP et al would require their own libraries. But introducing several new and tiny kernel modules for such small helpers wasn't worth it. Hence, there's the display library that can collect all such helpers in a single place.
Yes, I agree with your approach to have all helpers into a single module.
It looks like MIPI DSI could be another candidate to be moved into the display library; at least partially. I have go through the codebase to see if there are drivers that would benefit from such a change.
Great.
Best regards Thomas