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

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Message-ID: <Y+8upgx58a+vLeaT@kroah.com>
Date:   Fri, 17 Feb 2023 08:37:10 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Elliot Berman <quic_eberman@...cinc.com>
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 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?

> > > +	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.)

thanks,

greg k-h