linux-kernel - Re: [PATCH] binder: let ANDROID_BINDER_IPC

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Date:   Wed, 23 Aug 2017 11:01:51 +0800
From:   Jisheng Zhang <jszhang@...vell.com>
To:     John Stultz <john.stultz@...aro.org>
CC:     Greg KH <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Riley Andrews <riandrews@...roid.com>,
        <devel@...verdev.osuosl.org>, lkml <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] binder: let ANDROID_BINDER_IPC_32BIT be selectable on
 32bit ARM

On Tue, 22 Aug 2017 19:57:04 -0700 John Stultz wrote:

> On Tue, Aug 22, 2017 at 7:56 PM, John Stultz <john.stultz@...aro.org> wrote:
> > On Tue, Aug 22, 2017 at 7:34 PM, Jisheng Zhang <jszhang@...vell.com> wrote:  
> >> On Tue, 22 Aug 2017 18:51:08 -0700 Greg KH wrote:
> >>  
> >>> On Tue, Aug 08, 2017 at 07:03:05PM +0800, Jisheng Zhang wrote:  
> >>> > As noted in commit d0bdff0db809 ("staging: Fix build issues with new
> >>> > binder API"), we can add back the choice for 32bit ARM "once a 64bit
> >>> > __get_user_asm_* implementation is merged." Commit e38361d032f1 ("ARM:
> >>> > 8091/2: add get_user() support for 8 byte types") has added the
> >>> > support, so it's time to let ANDROID_BINDER_IPC_32BIT be selectable on
> >>> > 32bit ARM  
> >>>
> >>> Ok, but:
> >>>  
> >>> >
> >>> > Signed-off-by: Jisheng Zhang <jszhang@...vell.com>
> >>> > ---
> >>> >  drivers/android/Kconfig | 2 +-
> >>> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >>> >
> >>> > diff --git a/drivers/android/Kconfig b/drivers/android/Kconfig
> >>> > index 832e885349b1..aca5dc30b97b 100644
> >>> > --- a/drivers/android/Kconfig
> >>> > +++ b/drivers/android/Kconfig
> >>> > @@ -32,7 +32,7 @@ config ANDROID_BINDER_DEVICES
> >>> >       therefore logically separated from the other devices.
> >>> >
> >>> >  config ANDROID_BINDER_IPC_32BIT
> >>> > -   bool
> >>> > +   bool "Use old (Android 4.4 and earlier) 32-bit binder API"
> >>> >     depends on !64BIT && ANDROID_BINDER_IPC  
> >>>
> >>> You don't actually change the depends line :(
> >>>
> >>> Please fix up, and test it, and then resend.  
> >>
> >> IHOM, the dependency is correct: 64bit platforms don't support
> >> ANDROID_BINDER_IPC_32BIT. What do you think?  
> >
> > I think this indicates the commit message is unclear.
> >
> > Part of it is that the config is inverted from the description. The
> > patch doesn't enable the 32bit legacy binder ABI on 32bit systems, it
> > just allows the option to be unselected, so that the 64bit ABI will be
> > used on 32bit systems.
> >
> > Conceptually I don't have an objection to the change (though maybe try
> > to rework the commit message), but I don't have anything to actually
> > test it on right now, so I'm hesitant to ack it.  
> 
> It might also be good to add some detail as to the motivation for this
> change? What benefit does it bring to 32bit platforms to use the newer
> 64bit ABI?
> 

To be honest, the motivation is just to add one more choice for 32bit
platform and let the code be tested under 32bit platform. Maybe we
could then remove ANDROID_BINDER_IPC_32BIT and the related code after
some time?