Re: [PATCH] binder: let ANDROID_BINDER_IPC_32BIT be selectable on 32bit ARM

[Rob Herring]

On Tue, Aug 22, 2017 at 9:57 PM, John Stultz <john.stultz@xxxxxxxxxx> wrote:
> On Tue, Aug 22, 2017 at 7:56 PM, John Stultz <john.stultz@xxxxxxxxxx> wrote:
>> On Tue, Aug 22, 2017 at 7:34 PM, Jisheng Zhang <jszhang@xxxxxxxxxxx> 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@xxxxxxxxxxx>
>>>> > ---
>>>> >  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?

It allows running the same 32-bit userspace build whether the kernel
is 64-bit or 32-bit.

Rob