Re: [PATCH v8 09/28] mailbox: Add Gunyah message queue mailbox

From: Alex Elder <elder@linaro.org>
To: Elliot Berman <quic_eberman@quicinc.com>,
	Alex Elder <elder@linaro.org>,
	Bjorn Andersson <quic_bjorande@quicinc.com>,
	Jassi Brar <jassisinghbrar@gmail.com>,
	Murali Nalajala <quic_mnalajal@quicinc.com>,
	Jonathan Corbet <corbet@lwn.net>
Cc: Trilok Soni <quic_tsoni@quicinc.com>,
	Srivatsa Vaddagiri <quic_svaddagi@quicinc.com>,
	Carl van Schaik <quic_cvanscha@quicinc.com>,
	Prakruthi Deepak Heragu <quic_pheragu@quicinc.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Bagas Sanjaya <bagasdotme@gmail.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Lorenzo Pieralisi <lpieralisi@kernel.org>,
	Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
	linux-arm-msm@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, linux-acpi@vger.kernel.org
Subject: Re: [PATCH v8 09/28] mailbox: Add Gunyah message queue mailbox
Date: Tue, 17 Jan 2023 13:21:13 -0600	[thread overview]
Message-ID: <65af5abc-3719-95fe-041c-67d1d146aba1@linaro.org> (raw)
In-Reply-To: <f626a867-7293-fd70-00d7-706d43342f5f@quicinc.com>

On 1/10/23 12:16 PM, Elliot Berman wrote:
>>> +    ret = gh_hypercall_msgq_send(msgq->tx_ghrsc->capid, 
>>> msgq_data->length,
>>> +                    (uintptr_t)msgq_data->data, tx_flags, &ready);
>>> +
>>> +    /**
>>> +     * unlikely because Linux tracks state of msgq and should not 
>>> try to
>>> +     * send message when msgq is full.
>>> +     */
>>
>> Is it just unlikely, or is it impossible?
>>
> 
> This would require multiple mailbox controllers interacting with the 
> same message queue.
> 
> The only way I can think this is possible is if the Gunyah drivers are 
> unloaded when the message queue is full; drivers are then re-loaded 
> before the receiver processes the messages. The initial internal state 
> of the message queue controller assumes that there is space in the 
> message queue. We would get a Tx vIRQ once space becomes available and 
> the message would then be attempted to sent again. Since there's a safe 
> flow to recover from a inconsistent internal state and it's very 
> unlikely to start in that state, I don't think we need to add calls to 
> check if the message queue is full during initialization.

First, your explanation is appreciated but more than what I
was looking for...  I just mentioned it because if it were
impossible, then there's no point in having this code handle
something that literally can't happen.

But as far as your explanation, I *hope* if the Gunyah drivers
are unloaded, everything gets fully cleaned up before that
completes.  There should be no in-flight activity, or
any "previous generation" messages that could be processed.

In any case, I think my question is answered.  Thanks.

					-Alex

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel