linux-kernel - Re: [PATCH] drm/bridge: sil_sii8620: depend on INPUT instead of selecting it.

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Date:   Thu, 24 Jan 2019 00:22:00 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Lukas Wunner <lukas@...ner.de>,
        Ronald Tschalär <ronald@...ovation.ch>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Inki Dae <inki.dae@...sung.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-input@...r.kernel.org
Subject: Re: [PATCH] drm/bridge: sil_sii8620: depend on INPUT instead of
 selecting it.

Hello Dmity,

On Wed, Jan 23, 2019 at 02:21:05PM -0800, Dmitry Torokhov wrote:
> On Thu, Jan 24, 2019 at 12:17:35AM +0200, Laurent Pinchart wrote:
> > On Wed, Jan 23, 2019 at 02:03:42PM -0800, Dmitry Torokhov wrote:
> >> On Wed, Jan 23, 2019 at 09:45:56AM +0100, Lukas Wunner wrote:
> >>> On Tue, Jan 22, 2019 at 06:13:11AM -0800, Ronald Tschalär wrote:
> >>>> commit d6abe6df706c66d803e6dd4fe98c1b6b7f125a56 (drm/bridge:
> >>>> sil_sii8620: do not have a dependency of RC_CORE) added a dependency on
> >>>> INPUT. However, this causes problems with other drivers, in particular
> >>>> an input driver that depends on MFD_INTEL_LPSS_PCI (to be added in a
> >>>> future commit):
> >>>> 
> >>>>   drivers/clk/Kconfig:9:error: recursive dependency detected!
> >>>>   drivers/clk/Kconfig:9:        symbol COMMON_CLK is selected by MFD_INTEL_LPSS
> >>>>   drivers/mfd/Kconfig:566:      symbol MFD_INTEL_LPSS is selected by MFD_INTEL_LPSS_PCI
> >>>>   drivers/mfd/Kconfig:580:      symbol MFD_INTEL_LPSS_PCI is implied by KEYBOARD_APPLESPI
> >>>>   drivers/input/keyboard/Kconfig:73:    symbol KEYBOARD_APPLESPI depends on INPUT
> >>>>   drivers/input/Kconfig:8:      symbol INPUT is selected by DRM_SIL_SII8620
> >>>>   drivers/gpu/drm/bridge/Kconfig:83:    symbol DRM_SIL_SII8620 depends on DRM_BRIDGE
> >>>>   drivers/gpu/drm/bridge/Kconfig:1:     symbol DRM_BRIDGE is selected by DRM_PL111
> >>>>   drivers/gpu/drm/pl111/Kconfig:1:      symbol DRM_PL111 depends on COMMON_CLK
> >>>> 
> >>>> According to the docs, select should only be used for non-visible
> >>>> symbols. Furthermore almost all other references to INPUT throughout the
> >>>> kernel config are depends, not selects. Hence this change.
> >> 
> >> I think this is not as cut and dry. We should be able to select needed
> >> subsystems (such as INPUT, USB, etc) even if they are user visible.
> > 
> > Semantically, maybe, but given the current state of Kconfig this results
> > in a recursive dependencies nightmare. It's a no-go.
> > 
> >> User, when enabling a piece of hardware, does not need to know ultimate
> >> details of all subsystems the driver might need ti function.
> >> 
> >> It looks like one of the drivers implies MFD_INTEL_LPSS_PCI, maybe
> >> treating imply the same as select when detecting circular dependency is
> >> wrong as we are allowed to deselect implied dependencies?
> >> 
> >>>> 
> >>>> CC: Inki Dae <inki.dae@...sung.com>
> >>>> CC: Andrzej Hajda <a.hajda@...sung.com>
> >>>> Signed-off-by: Ronald Tschalär <ronald@...ovation.ch>
> >>> 
> >>> Reviewed-by: Lukas Wunner <lukas@...ner.de>
> >>> 
> >>> I think this needs to be merged through the input tree as a prerequisite
> >>> for the applespi.c driver (keyboard + touchpad driver for 2015+ MacBook,
> >>> MacBook Air and MacBook Pro which uses SPI instead of USB) to avoid
> >>> breaking the build.  Adding Dmitry.
> >> 
> >> I have no idea what applespi.c is (it is definitely not in my tree), so
> >> I think it should be merged through the same tree that the original
> >> commit was introduced through.
> >> 
> >>>> ---
> >>>>  drivers/gpu/drm/bridge/Kconfig | 2 +-
> >>>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>> 
> >>>> diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> >>>> index 2fee47b0d50b..eabedc83f25c 100644
> >>>> --- a/drivers/gpu/drm/bridge/Kconfig
> >>>> +++ b/drivers/gpu/drm/bridge/Kconfig
> >>>> @@ -83,9 +83,9 @@ config DRM_PARADE_PS8622
> >>>>  config DRM_SIL_SII8620
> >>>>  	tristate "Silicon Image SII8620 HDMI/MHL bridge"
> >>>>  	depends on OF
> >>>> +	depends on INPUT
> >>>>  	select DRM_KMS_HELPER
> >>>>  	imply EXTCON
> >>>> -	select INPUT
> >>>>  	select RC_CORE
> >> 
> >> Keeping "select RC_CORE" is wrong though, as the driver appears to be
> >> working find without RC. Maybe it should be stubbed out?
> > 
> > It should definitely not be select'ed as it's a user-visible symbol. My
> > preference would be to simply revert d6abe6df706c. If we want (and can)
> > work without RC core then it should be stubbed out.
> > 
> > Commit d6abe6df706c states
> > 
> >     And some boards not using remote controller device don't really
> >     need to know that RC_CORE config should be enabled to use sil_sii8620
> >     driver only for HDMI.
> > 
> > The same reasoning applies to INPUT, if we agree that depending on
> > RC_CORE is confusing for users, then depending on INPUT is confusing as
> > well. There's not reason to apply different standards to INPUT and
> > RC_CORE, depending on one and selecting the other doesn't make much
> > sense.
> 
> OK, so revert + patch to stub out RC calls? That works for me (and I
> still say it should go through the same tree that introduced
> d6abe6df706c).

Yes, that sounds good to me.

-- 
Regards,

Laurent Pinchart