linux-kernel - Re: [PATCH v10 08/26] gunyah: rsc_mgr: Add resource manager RPC core

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Message-ID: <931494e0-b2da-5746-a86c-42b972072080@quicinc.com>
Date:   Wed, 22 Feb 2023 14:52:07 -0800
From:   Elliot Berman <quic_eberman@...cinc.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     Alex Elder <elder@...aro.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Prakruthi Deepak Heragu <quic_pheragu@...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>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        "Arnd Bergmann" <arnd@...db.de>, Rob Herring <robh+dt@...nel.org>,
        "Krzysztof Kozlowski" <krzysztof.kozlowski+dt@...aro.org>,
        Jonathan Corbet <corbet@....net>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        Catalin Marinas <catalin.marinas@....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 08/26] gunyah: rsc_mgr: Add resource manager RPC core



On 2/16/2023 11:37 PM, Greg Kroah-Hartman wrote:
> On Thu, Feb 16, 2023 at 09:40:52AM -0800, Elliot Berman wrote:
>>
>>
>> On 2/15/2023 10:43 PM, Greg Kroah-Hartman wrote:
>>> On Tue, Feb 14, 2023 at 01:23:25PM -0800, Elliot Berman wrote:
>>>> +struct gh_rm {
>>>> +	struct device *dev;
>>>
>>> What device does this point to?
>>>
>>
>> The platform device.
> 
> What platform device?  And why a platform device?
> 

This will be used for the dev_printk. It's presently also used for the 
reference counting. From your comments below, I'll switch the reference 
counting away from this platform device.

>>>> +	struct gunyah_resource tx_ghrsc, rx_ghrsc;
>>>> +	struct gh_msgq msgq;
>>>> +	struct mbox_client msgq_client;
>>>> +	struct gh_rm_connection *active_rx_connection;
>>>> +	int last_tx_ret;
>>>> +
>>>> +	struct idr call_idr;
>>>> +	struct mutex call_idr_lock;
>>>> +
>>>> +	struct kmem_cache *cache;
>>>> +	struct mutex send_lock;
>>>> +	struct blocking_notifier_head nh;
>>>> +};
>>>
>>> This obviously is the "device" that your system works on, so what are
>>> the lifetime rules of it?  Why isn't is just a real 'struct device' in
>>> the system instead of a random memory blob with a pointer to a device?
>>>
>>> What controls the lifetime of this structure and where is the reference
>>> counting logic for it?
>>>
>>
>> The lifetime of the structure is bound by the platform device that above
>> struct device *dev points to. get_gh_rm and put_gh_rm increments the device
>> ref counter and ensures lifetime of the struct is also extended.
> 
> But this really is "your" device, not the platform device.  So make it a
> real one please as that is how the kernel's driver model works.  Don't
> hang "magic structures" off of a random struct device and have them
> control the lifetime rules of the parent without actually being a device
> themself.  This should make things simpler overall, not more complex,
> and allow you to expose things to userspace properly (right now your
> data is totally hidden.)

The "real" device I create here is the miscdev, so I think the 
recommendation here is to do refcounting off that miscdev. Is this the 
approach you were thinking of?

Thanks,
Elliot