linux-kernel - Re: [PATCH v2] misc: fastrpc: Fix channel resource access in device

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Message-ID: <2025062424-dizziness-theft-0502@gregkh>
Date: Tue, 24 Jun 2025 16:36:35 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Ekansh Gupta <ekansh.gupta@....qualcomm.com>,
	srinivas.kandagatla@...aro.org, linux-arm-msm@...r.kernel.org,
	quic_bkumar@...cinc.com, linux-kernel@...r.kernel.org,
	quic_chennak@...cinc.com, dri-devel@...ts.freedesktop.org,
	arnd@...db.de, stable@...nel.org
Subject: Re: [PATCH v2] misc: fastrpc: Fix channel resource access in
 device_open

On Tue, Jun 24, 2025 at 04:27:21PM +0300, Dmitry Baryshkov wrote:
> On Thu, Jun 19, 2025 at 10:40:26AM +0530, Ekansh Gupta wrote:
> > During rpmsg_probe, fastrpc device nodes are created first, then
> > channel specific resources are initialized, followed by
> > of_platform_populate, which triggers context bank probing. This
> > sequence can cause issues as applications might open the device
> > node before channel resources are initialized or the session is
> > available, leading to problems. For example, spin_lock is initialized
> > after the device node creation, but it is used in device_open,
> > potentially before initialization. Move device registration after
> > channel resource initialization in fastrpc_rpmsg_probe.
> 
> You've moved device init, however there is still a possibility for the
> context devices to be created, but not bound to the driver (because all
> the probings are async). I think instead we should drop the extra
> platform driver layer and create and set up corresponding devices
> manually. For example, see how it is handled in
> host1x_memory_context_list_init(). That function uses iommu-maps, but we
> can use OF nodes and iommus instead.

Is this a real platform device?  If so, why do you need a second
platform driver, what makes this so unique?  If this isn't a platform
device, then why not just use the faux bus instead?

It seems that "number of sessions" is a DT property, is that something
that is really defined by the hardware?  Or is it just a virtual thing
that people are abusing in the DT?

And if you really have all these sessions, why not make them real
devices, wouldn't that make things simpler?

thanks,

greg k-h