linux-kernel - Re: [PATCH v9 17/19] drm/virtio: kconfig: Fix recursive dependency issue.

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Date:   Thu, 6 Oct 2016 11:45:41 +0100
From:   Emil Velikov <emil.l.velikov@...il.com>
To:     Peter Griffin <peter.griffin@...aro.org>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>,
        Ohad Ben-Cohen <ohad@...ery.com>,
        devicetree <devicetree@...r.kernel.org>, kernel@...inux.com,
        vinod.koul@...el.com, Lee Jones <lee.jones@...aro.org>,
        linux-remoteproc@...r.kernel.org, patrice.chotard@...com,
        ML dri-devel <dri-devel@...ts.freedesktop.org>,
        "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        Gerd Hoffmann <kraxel@...hat.com>, dmaengine@...r.kernel.org,
        dan.j.williams@...el.com,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        "open list:VIRTIO GPU DRIVER" 
        <virtualization@...ts.linux-foundation.org>,
        LAKML <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v9 17/19] drm/virtio: kconfig: Fix recursive dependency issue.

On 6 October 2016 at 10:37, Peter Griffin <peter.griffin@...aro.org> wrote:

> In fact the help text for VIRTIO even states this option should be selected
> by any driver which implements virtio.
>
Almost but not quite. It says:

"This option is selected by any driver which implements the virtio _bus_"

REMOTEPROC obviously does that while the ST SLIM driver does not. Thus
the latter should _not_ select, be that explicitly or implicitly via
REMOTEPROC, the symbol.

>>
>> People tend to abuse select because it's "convenient". If you depend,
>> but some of your dependencies aren't met, you're in for some digging
>> through Kconfig to find the missing deps. Just to make the option you
>> want visible in menuconfig. If you instead select something with
>> dependencies, it'll be right most of the time, and it's "convenient",
>> until it breaks. (And hey, it usually breaks for someone else with some
>> other config, so it's still convenient for you.)
>
> I'm sure they do but in this case it is actually the use of 'depends on'
> which has caused the breakage and inconvenience for somebody else and sadly this
> inconvienice is still on-going due to this patch not being applied or getting an
> acked-by from the appropriate maintainers.
>
Surely you're not saying that pre-existing driver following the
documentation, is 'causing breakage' for a new driver {ab,mis}using a
feature ?

This reminds me an old saying: "If the shoe doesn’t fit, it doesn’t
mean there is anything wrong with your feet."
You seem to be suggesting the opposite ?

>>
>> Perhaps kconfig should complain about selecting visible symbols and
>> symbols with dependencies.
>
> That sounds like it would be a useful addition.
>
> Is it possible to get this patch applied or an acked-by to avoid further delay
> to the fdma series?
>
Please don't apply duct tape, especially where it's _not_ needed.

$ sed -i s/select REMOTEPROC/depends on REMOTEPROC/ drivers/remoteproc/Kconfig

... will resolve things in the right place. The alternative will lead
to random issues in other subsystems.

Regards,
Emil