Re: [PATCH v2] misc: fastrpc: Fix channel resource access in device_open

[Ekansh Gupta <ekansh.gupta@oss.qualcomm.com>]

On 6/25/2025 5:15 AM, Dmitry Baryshkov wrote:
> On Tue, Jun 24, 2025 at 04:38:25PM +0100, Greg KH wrote:
>> On Tue, Jun 24, 2025 at 04:36:35PM +0100, Greg KH wrote:
>>> 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?
> Purely software value.
>
>>> And if you really have all these sessions, why not make them real
>>> devices, wouldn't that make things simpler?
>> Oh wait, these are "fake" platform devices under the parent (i.e. real)
>> platform device.  That's not good, please don't do that, use the faux
>> bus code now instead to properly handle this.  Attempting to create a
>> device when open() is called is really really odd...
> The driver doesn't created devices during open(). It creates them
> earlier, then another driver probes an populates the data. I suggest to
> follow Tegra approach, remove the sub-driver completely and instead of
> calling of_platform_populate() create necessary devices manually and set
> corresponding IOMMU configuration from the main driver's probe path.
Thanks for the suggestions. I'm checking this approach.
>