linux-kernel - Re: [PATCH] usb: typec: nb7vpq904m: add CONFIG

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Date:   Thu, 22 Jun 2023 17:39:05 +0200
From:   Neil Armstrong <neil.armstrong@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>, Arnd Bergmann <arnd@...nel.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Bjorn Andersson <andersson@...nel.org>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: typec: nb7vpq904m: add CONFIG_DRM dependency

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@...db.de>
>>>
>>> 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@...db.de>
>>> ---
>>>    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