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SubjectRe: [PATCH v2 2/2] drivers: gpio: add virtio-gpio guest driver
On Sat, Dec 05, 2020 at 09:05:16PM +0100, Enrico Weigelt, metux IT consult wrote:
> On 05.12.20 20:32, Michael S. Tsirkin wrote:
>
> Hi,
>
> > It seems a bit of a mess, at this point I'm not entirely sure when
> > should drivers select VIRTIO and when depend on it.
>
> if VIRTIO just enables something that could be seen as library
> functions, then select should be right, IMHO.
>
> > The text near it says:
> >
> > # SPDX-License-Identifier: GPL-2.0-only
> > config VIRTIO
> > tristate
>
> oh, wait, doesn't have an menu text, so we can't even explicitly enable
> it (not shown in menu) - only implicitly. Which means that some other
> option must select it, in order to become availe at all, and in order
> to make others depending on it becoming available.
>
> IMHO, therefore select is the correct approach.
>
>
> > help
> > This option is selected by any driver which implements the virtio
> > bus, such as CONFIG_VIRTIO_PCI, CONFIG_VIRTIO_MMIO, CONFIG_RPMSG
> > or CONFIG_S390_GUEST.
> >
> > Which seems clear enough and would indicate drivers for devices *behind*
> > the bus should not select VIRTIO and thus presumably should "depend on" it.
> > This is violated in virtio console and virtio fs drivers.
>
> See above: NAK. because it can't even be enabled directly (by the user).
> If it wasn't meant otherwise, we'd have to add an menu text.


The point is that user enables one of the bindings.
That in turn enables drivers. If we merely select VIRTIO
there's a chance user won't remember to select any bindings
and will be surprised not to see any devices.



> > For console it says:
> >
> > commit 9f30eb29c514589e16f2999ea070598583d1f6ec
> > Author: Michal Suchanek <msuchanek@suse.de>
> > Date: Mon Aug 31 18:58:50 2020 +0200
> >
> > char: virtio: Select VIRTIO from VIRTIO_CONSOLE.
> >
> > Make it possible to have virtio console built-in when
> > other virtio drivers are modular.
> >
> > Signed-off-by: Michal Suchanek <msuchanek@suse.de>
> > Reviewed-by: Amit Shah <amit@kernel.org>
> > Link: https://lore.kernel.org/r/20200831165850.26163-1-msuchanek@suse.de
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> >
> > which seems kind of bogus - why do we care about allowing a builtin
> > virtio console driver if the pci virtio bus driver is a module?
> > There won't be any devices on the bus to attach to ...
>
> When using other transports ?

Any transport selects VIRTIO so if you enable that, you get
VIRTIO and thus it's enough to depend on it.

> In my current project, eg. I'm using mmio - my kernel has pci completely
> disabled.
>
> > I am inclined to fix console and virtio fs to depend on VIRTIO:
> > select is harder to use correctly ...
>
> I don't thinkt that would be good - instead everybody should just select
> VIRTIO, never depend on it (maybe depend on VIRTIO_MENU instead)

GPU depends on VIRTIO and on VIRTIO_MENU ... which seems even messier
...

>
> --mtx
>
> --
> ---
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> ---
> Enrico Weigelt, metux IT consult
> Free software and Linux embedded engineering
> info@metux.net -- +49-151-27565287

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