[PATCH 3/8] drm/display: Introduce a DRM display-helper module

[Javier Martinez Canillas]

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 at 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
> 
>>
> 

-- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat