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

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Message-ID: <988aa0ec-c6a1-70ce-cd4d-abc2b2948323@linaro.org>
Date:   Thu, 22 Jun 2023 18:05:32 +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

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