Re: [PATCH 6.2 regression fix] drm/nouveau/kms: Fix backlight registration

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 3/29/23 00:23, Lyude Paul wrote:
> Reviewed-by: Lyude Paul <lyude@redhat.com>
> 
> (Also note to Mark: this is my way of letting you know someone fixed the
> regression with backlight controls upstream, looking into the weird bright
> screen after resume issue)

Thanks.

I have pushed this to drm-misc-fixes now.

I'll also submit a downstream Fedora kernel pull-req with this
to get this resolved in the Fedora kernels .

Regards,

Hans



> 
> On Sun, 2023-03-26 at 22:54 +0200, Hans de Goede wrote:
>> The nouveau code used to call drm_fb_helper_initial_config() from
>> nouveau_fbcon_init() before calling drm_dev_register(). This would
>> probe all connectors so that drm_connector->status could be used during
>> backlight registration which runs from nouveau_connector_late_register().
>>
>> After commit 4a16dd9d18a0 ("drm/nouveau/kms: switch to drm fbdev helpers")
>> the fbdev emulation code, which now is a drm-client, can only run after
>> drm_dev_register(). So during backlight registration the connectors are
>> not probed yet and the drm_connector->status == connected check in
>> nv50_backlight_init() would now always fail.
>>
>> Replace the drm_connector->status == connected check with
>> a drm_helper_probe_detect() == connected check to fix nv_backlight
>> no longer getting registered because of this.
>>
>> Fixes: 4a16dd9d18a0 ("drm/nouveau/kms: switch to drm fbdev helpers")
>> Link: https://gitlab.freedesktop.org/drm/nouveau/-/issues/202
>> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
>> ---
>>  drivers/gpu/drm/nouveau/nouveau_backlight.c | 7 ++++++-
>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/nouveau/nouveau_backlight.c b/drivers/gpu/drm/nouveau/nouveau_backlight.c
>> index 40409a29f5b6..91b5ecc57538 100644
>> --- a/drivers/gpu/drm/nouveau/nouveau_backlight.c
>> +++ b/drivers/gpu/drm/nouveau/nouveau_backlight.c
>> @@ -33,6 +33,7 @@
>>  #include <linux/apple-gmux.h>
>>  #include <linux/backlight.h>
>>  #include <linux/idr.h>
>> +#include <drm/drm_probe_helper.h>
>>  
>>  #include "nouveau_drv.h"
>>  #include "nouveau_reg.h"
>> @@ -299,8 +300,12 @@ nv50_backlight_init(struct nouveau_backlight *bl,
>>  	struct nouveau_drm *drm = nouveau_drm(nv_encoder->base.base.dev);
>>  	struct nvif_object *device = &drm->client.device.object;
>>  
>> +	/*
>> +	 * Note when this runs the connectors have not been probed yet,
>> +	 * so nv_conn->base.status is not set yet.
>> +	 */
>>  	if (!nvif_rd32(device, NV50_PDISP_SOR_PWM_CTL(ffs(nv_encoder->dcb->or) - 1)) ||
>> -	    nv_conn->base.status != connector_status_connected)
>> +	    drm_helper_probe_detect(&nv_conn->base, NULL, false) != connector_status_connected)
>>  		return -ENODEV;
>>  
>>  	if (nv_conn->type == DCB_CONNECTOR_eDP) {
>