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

[Neil Armstrong]

Hi,

On 22/06/2023 13:24, Arnd Bergmann wrote:
> On Thu, Jun 22, 2023, at 12:39, Neil Armstrong wrote:
> > Hi,
> >
> > On 22/06/2023 12:18, Arnd Bergmann wrote:
> > > From: Arnd Bergmann <arnd@xxxxxxxx>
> > >
> > > This driver calls directly into DRM functions and fails to link if
> > > that is disabled:
> > >
> > > ld.lld: error: undefined symbol: devm_drm_bridge_add
> > > ld.lld: error: undefined symbol: devm_drm_of_get_bridge
> > > > > > referenced by nb7vpq904m.c
> > > > > >                 drivers/usb/typec/mux/nb7vpq904m.o:(nb7vpq904m_probe) in archive vmlinux.a
> > >
> > > Fixes: 88d8f3ac9c67e ("usb: typec: add support for the nb7vpq904m Type-C Linear Redriver")
> > > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> > > ---
> > >    drivers/usb/typec/mux/Kconfig | 2 +-
> > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/usb/typec/mux/Kconfig b/drivers/usb/typec/mux/Kconfig
> > > index 8c4d6b8fb75c3..f53ae24b6c048 100644
> > > --- a/drivers/usb/typec/mux/Kconfig
> > > +++ b/drivers/usb/typec/mux/Kconfig
> > > @@ -37,7 +37,7 @@ config TYPEC_MUX_INTEL_PMC
> > >    
> > >    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)

so I wonder which kind on config leaded to that since
CONFIG_DRM_PANEL_BRIDGE is only enabled when DRM_PANEL and DRM are.

Neil

>      Arnd