Subject: Re: [RFC PATCH] s390: vfio-ap: Register the vfio_ap module for the
 "ap" parent bus
To:     Thomas Huth <thuth@redhat.com>, linux-s390@vger.kernel.org,
        Tony Krowiak <akrowiak@linux.ibm.com>,
        Halil Pasic <pasic@linux.ibm.com>,
        Jason Herne <jjherne@linux.ibm.com>
Cc:     linux-kernel@vger.kernel.org, Heiko Carstens <hca@linux.ibm.com>,
        Vasily Gorbik <gor@linux.ibm.com>
References: <20211201141110.94636-1-thuth@redhat.com>
From:   Harald Freudenberger <freude@linux.ibm.com>
Message-ID: <210e3c57-bdc2-09ed-3e41-8dab57e8f36c@linux.ibm.com>
Date:   Wed, 1 Dec 2021 18:10:04 +0100
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On 01.12.21 15:11, Thomas Huth wrote:
> The crypto devices that we can use with the vfio_ap module are sitting
> on the "ap" bus, not on the "vfio_ap" bus that the module defines
> itself. With this change, the vfio_ap module now gets automatically
> loaded if a supported crypto adapter is available in the host.
>
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  Note: Marked as "RFC" since I'm not 100% sure about it ...
>        please review carefully!
>
>  drivers/s390/crypto/vfio_ap_drv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/s390/crypto/vfio_ap_drv.c b/drivers/s390/crypto/vfio_ap_drv.c
> index 4d2556bc7fe5..5580e40608a4 100644
> --- a/drivers/s390/crypto/vfio_ap_drv.c
> +++ b/drivers/s390/crypto/vfio_ap_drv.c
> @@ -39,7 +39,7 @@ static struct ap_device_id ap_queue_ids[] = {
>  	{ /* end of sibling */ },
>  };
>  
> -MODULE_DEVICE_TABLE(vfio_ap, ap_queue_ids);
> +MODULE_DEVICE_TABLE(ap, ap_queue_ids);
>  
>  /**
>   * vfio_ap_queue_dev_probe:
Hello Thomas, interesting.
Did you test this ? I mean did you build a kernel and have it run on a s390 with crypto cards available ?
My strong feeling is that this will make the AP bus code stumble as the code silently assumes there are exact
two types of ap devices attached to the ap bus: ap cards and ap queues. This is a fair assumption as the ap bus
is the 'owner' of what's attached to the bus it maintains. But with this change and no further arrangements
in the ap bus code my feeling is ...
However, Tony is the owner of the vfio ap stuff, so maybe he has another opinion.
Harald Freudenberger