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Subject: Re: [PATCH v3 -next] vdpa: mlx5: change Kconfig depends to fix build
 errors
To:     "Michael S. Tsirkin" <mst@redhat.com>,
        Leon Romanovsky <leonro@nvidia.com>
Cc:     Randy Dunlap <rdunlap@infradead.org>, Eli Cohen <elic@nvidia.com>,
        virtualization@lists.linux-foundation.org,
        LKML <linux-kernel@vger.kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        Saeed Mahameed <saeedm@nvidia.com>
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From:   Jason Wang <jasowang@redhat.com>
Message-ID: <821c501c-53ce-3e80-8a73-f0680193df20@redhat.com>
Date:   Fri, 25 Sep 2020 19:29:24 +0800
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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


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