linux-kernel - Re: [PATCH v10 04/26] virt: gunyah: Add hypercalls to identify Gunyah

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Message-ID: <d01e4b1f-862b-410f-66bb-9b8158e76807@quicinc.com>
Date:   Wed, 1 Mar 2023 17:21:53 -0800
From:   Elliot Berman <quic_eberman@...cinc.com>
To:     Alex Elder <alex.elder@...aro.org>, Alex Elder <elder@...aro.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        "Prakruthi Deepak Heragu" <quic_pheragu@...cinc.com>
CC:     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>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Bjorn Andersson <andersson@...nel.org>,
        "Konrad Dybcio" <konrad.dybcio@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Jonathan Corbet <corbet@....net>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        Jassi Brar <jassisinghbrar@...il.com>,
        <linux-arm-msm@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v10 04/26] virt: gunyah: Add hypercalls to identify Gunyah



On 2/23/2023 4:09 PM, Alex Elder wrote:
> On 2/14/23 3:12 PM, Elliot Berman wrote:
>> +
>> +void gh_hypercall_hyp_identify(struct gh_hypercall_hyp_identify_resp 
>> *hyp_identity);
> 
> Since this is a user space API, you *could* consider having
> this function return an int.  Just in case there's a future
> reason that a failure could occur, or that you want to
> supply some other information.  If this truly doesn't make
> sense, it's fine as-is...
> 

I'm not sure what was meant by user space API. However, hypervisor API 
doesn't provision a return value. r0 is usually the return value for 
most other Gunyah hypercalls except for this one -- instead, it's the 
api_info field.

The other kind of error we could get is at hypercall "transport" layer, 
but the hvc instruction doesn't fail and if we ever change the hypercall 
transport, I'm sure there will be a lot of other changes to consider as 
well.

Thanks,
Elliot