linux-kernel - Re: [PATCH v4 10/14] gunyah: sysfs: Add node to describe supported features

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Date:   Fri, 30 Sep 2022 14:06:30 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Elliot Berman <quic_eberman@...cinc.com>
Cc:     Bjorn Andersson <quic_bjorande@...cinc.com>,
        Murali Nalajala <quic_mnalajal@...cinc.com>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        Srivatsa Vaddagiri <quic_svaddagi@...cinc.com>,
        Carl van Schaik <quic_cvanscha@...cinc.com>,
        Andy Gross <agross@...nel.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Jassi Brar <jassisinghbrar@...il.com>,
        linux-arm-kernel@...ts.infradead.org,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Marc Zyngier <maz@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Jonathan Corbet <corbet@....net>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Arnd Bergmann <arnd@...db.de>, devicetree@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 10/14] gunyah: sysfs: Add node to describe supported
 features

On Wed, Sep 28, 2022 at 12:56:29PM -0700, Elliot Berman wrote:
> Add a sysfs node to list the features that the Gunyah hypervisor and
> Linux supports. For now, Linux support cspace (capability IDs) and
> message queues, so only report those..
> 
> Signed-off-by: Elliot Berman <quic_eberman@...cinc.com>
> ---
>  Documentation/ABI/testing/sysfs-hypervisor-gunyah | 15 +++++++++++++++
>  drivers/virt/gunyah/sysfs.c                       | 15 +++++++++++++++
>  2 files changed, 30 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-hypervisor-gunyah b/Documentation/ABI/testing/sysfs-hypervisor-gunyah
> index 7d74e74e9edd..6d0cde30355a 100644
> --- a/Documentation/ABI/testing/sysfs-hypervisor-gunyah
> +++ b/Documentation/ABI/testing/sysfs-hypervisor-gunyah
> @@ -1,3 +1,18 @@
> +What:		/sys/hypervisor/gunyah/features
> +Date:		October 2022
> +KernelVersion:	6.1
> +Contact:	linux-arm-msm@...r.kernel.org
> +Description:	If running under Gunyah:
> +		Space separated list of features supported by Linux and Gunyah:
> +		"cspace": Gunyah devices
> +		"doorbell": Sending/receiving virtual interrupts via Gunyah doorbells
> +		"message-queue": Sending/receiving messages via Gunyah message queues
> +		"vic": Interrupt lending
> +		"vpm": Virtual platform management
> +		"vcpu": Virtual CPU management
> +		"memextent": Memory lending/management
> +		"trace": Gunyah hypervisor tracing

Please no.  Why do you really need this type of list?  What hypervisor
will NOT have them all present already?  Who will use this file and what
will it be used for?

sysfs files should just be 1 value and not need to be parsed.  Yes, we
have lists of features at times, but really, you need a very very good
reason why this is the only way this information can be exposed and who
is going to use it in order to be able to have this accepted.

thanks,

greg k-h