Re: [PATCH] usb: typec: nb7vpq904m: add CONFIG_DRM dependency

[Neil Armstrong]

On 22/06/2023 17:57, Arnd Bergmann wrote:
> On Thu, Jun 22, 2023, at 17:39, Neil Armstrong wrote:
> > On 22/06/2023 13:24, Arnd Bergmann wrote:
> > > On Thu, Jun 22, 2023, at 12:39, Neil Armstrong wrote:
> > > > >     
> > > > >     config TYPEC_MUX_NB7VPQ904M
> > > > >     	tristate "On Semiconductor NB7VPQ904M Type-C redriver driver"
> > > > > -	depends on I2C
> > > > > +	depends on I2C && DRM
> > > > >     	select REGMAP_I2C
> > > > >     	help
> > > > >     	  Say Y or M if your system has a On Semiconductor NB7VPQ904M Type-C
> > > >
> > > > I think it could be :
> > > >
> > > > +	depends on DRM || DRM=n
> > > > +	select DRM_PANEL_BRIDGE if DRM
> > >
> > > As far as I can tell, this would only avoid the link error
> > > against devm_drm_of_get_bridge(), but not the one against
> > > devm_drm_bridge_add(), which is defined in drm.ko through
> > > drivers/gpu/drm/drm_bridge.c.
> >
> > I'm trying to reproduce such situation, but so fail I fail.
> >
> > In the driver there's a guard to avoid calling into DRM functions
> > when disabled:
> > #if IS_ENABLED(CONFIG_OF) && IS_ENABLED(CONFIG_DRM_PANEL_BRIDGE)
>
> Ah, you are right. I got confused because the check is in
> header file for devm_drm_of_get_bridge(), but not for
> devm_drm_bridge_add(), which has the check in the source
> file as you point out.
>
> > so I wonder which kind on config leaded to that since
> > CONFIG_DRM_PANEL_BRIDGE is only enabled when DRM_PANEL and DRM are.
>
> I only saw the original issue with
>
> CONFIG_DRM=m
> CONFIG_DRM_PANEL=y
> CONFIG_DRM_BRIDGE=y
> CONFIG_DRM_PANEL_BRIDGE=y
> CONFIG_TYPEC_MUX_NB7VPQ904M=y

Ok now I see it

> and since CONFIG_DRM_PANEL_BRIDGE already depends on CONFIG_DRM,
> I think that is the only one that can go wrong, so your
> suggestion of
>
>     depends on DRM || DRM=n
>
> should be sufficient. I see that DRM_PANEL, DRM_BRIDGE and
> DRM_PANEL_BRIDGE are now always =y whenever DRM is enabled,
> so I don't think the 'select CONFIG_DRM_PANEL_BRIDGE' serves
> any purpose any more, but it's also harmless if you think it
> helps for clarification.

Yes DRM || DRM=n seems sufficient, but having
select DRM_PANEL_BRIDGE if DRM could clarify things.

> Can you send the updated patch, or should I?

I'll send an updated patch,

Thanks,
Neil

>       Arnd