linux-kernel - Re: [PATCH v3 -next] vdpa: mlx5: change Kconfig depends to fix build errors

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Date:   Sat, 26 Sep 2020 09:53:08 +0300
From:   Leon Romanovsky <leonro@...dia.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Eli Cohen <elic@...dia.com>,
        virtualization@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [PATCH v3 -next] vdpa: mlx5: change Kconfig depends to fix build
 errors

On Fri, Sep 25, 2020 at 07:29:24PM +0800, Jason Wang wrote:
>
> On 2020/9/25 下午6:19, Michael S. Tsirkin wrote:
> > On Fri, Sep 25, 2020 at 10:20:05AM +0300, Leon Romanovsky wrote:
> > > On Thu, Sep 24, 2020 at 12:02:43PM -0400, Michael S. Tsirkin wrote:
> > > > On Thu, Sep 24, 2020 at 08:47:05AM -0700, Randy Dunlap wrote:
> > > > > On 9/24/20 3:24 AM, Eli Cohen wrote:
> > > > > > On Thu, Sep 24, 2020 at 05:30:55AM -0400, Michael S. Tsirkin wrote:
> > > > > > > > > --- linux-next-20200917.orig/drivers/vdpa/Kconfig
> > > > > > > > > +++ linux-next-20200917/drivers/vdpa/Kconfig
> > > > > > > > > @@ -31,7 +31,7 @@ config IFCVF
> > > > > > > > >
> > > > > > > > >   config MLX5_VDPA
> > > > > > > > >   	bool "MLX5 VDPA support library for ConnectX devices"
> > > > > > > > > -	depends on MLX5_CORE
> > > > > > > > > +	depends on VHOST_IOTLB && MLX5_CORE
> > > > > > > > >   	default n
> > > > > > > > While we are here, can anyone who apply this patch delete the "default n" line?
> > > > > > > > It is by default "n".
> > > > > > I can do that
> > > > > >
> > > > > > > > Thanks
> > > > > > > Hmm other drivers select VHOST_IOTLB, why not do the same?
> > > > > v1 used select, but Saeed requested use of depends instead because
> > > > > select can cause problems.
> > > > >
> > > > > > I can't see another driver doing that. Perhaps I can set dependency on
> > > > > > VHOST which by itself depends on VHOST_IOTLB?
> > > > > > >
> > > > > > > > >   	help
> > > > > > > > >   	  Support library for Mellanox VDPA drivers. Provides code that is
> > > > > > > > >
> > > > Saeed what kind of problems? It's used with select in other places,
> > > > isn't it?
> > > IMHO, "depends" is much more explicit than "select".
> > >
> > > Thanks
> > This is now how VHOST_IOTLB has been designed though.
> > If you want to change VHOST_IOTLB to depends I think
> > we should do it consistently all over.
> >
> >
> > config VHOST_IOTLB
> >          tristate
> >          help
> >            Generic IOTLB implementation for vhost and vringh.
> >            This option is selected by any driver which needs to support
> >            an IOMMU in software.
>
>
> Yes, since there's no prompt for VHOST_IOTLB which means, if there's no
> other symbol that select VHOST_IOTLB, you can't enable MLX5 at all.
>
> See kconfig-language.rst:
>
>
>     In general use select only for non-visible symbols
>     (no prompts anywhere) and for symbols with no dependencies.
>     That will limit the usefulness but on the other hand avoid
>     the illegal configurations all over.

Thanks, I wasn't aware of this clarification.

>
> Thanks
>
>
> >
> >
> > > > > --
> > > > > ~Randy
>