linux-kernel - Re: [PATCH V1 1/2] soc: qcom: aoss: Expose send for generic usecase

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Date:   Fri, 9 Apr 2021 13:01:53 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Deepak Kumar Singh <deesin@...eaurora.org>, clew@...eaurora.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-remoteproc@...r.kernel.org, Andy Gross <agross@...nel.org>
Subject: Re: [PATCH V1 1/2] soc: qcom: aoss: Expose send for generic usecase

On Sun, Apr 04, 2021 at 12:17:52PM -0500, Bjorn Andersson wrote:
> On Fri 02 Apr 01:17 CDT 2021, Deepak Kumar Singh wrote:
> 
> > Not all upcoming usecases will have an interface to allow the aoss
> > driver to hook onto. Expose the send api and create a get function to
> > enable drivers to send their own messages to aoss.
> > 
> > Signed-off-by: Chris Lew <clew@...eaurora.org>
> > Signed-off-by: Deepak Kumar Singh <deesin@...eaurora.org>
> > ---
> >  drivers/soc/qcom/qcom_aoss.c | 36 +++++++++++++++++++++++++++++++++++-
> >  1 file changed, 35 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/soc/qcom/qcom_aoss.c b/drivers/soc/qcom/qcom_aoss.c
> > index 53acb94..5c643f0 100644
> > --- a/drivers/soc/qcom/qcom_aoss.c
> > +++ b/drivers/soc/qcom/qcom_aoss.c
> > @@ -8,10 +8,12 @@

[...]

> > +	pdev = of_find_device_by_node(np);
> 
> of_find_device_by_node() will increment the refcount of the underlying
> struct device of pdev, so you need to platform_device_put() once you're
> done with it.
> 
> As a side effect of not putting the struct device, the devm_kzalloc'ed
> qmp pointer will remain valid. So care is needed to make sure that the
> client doesn't end up with a dangling pointer if the qmp device is
> removed.
> 
> My suggestion is that you add a "qmp_put()" function, which invokes
> platform_device_put() and that you add some sort of tracking ("bool
> orphan"?) to the struct qmp and make qmp_send() fail if this is set.
> 

I think this is a duplication of what the struct device offers. Why
can't we use the generic infrastructure for this usecase?

Like using device_initialize() in qmp_probe() along with a release
callback for "struct device", then using get_device() in qmp_get().
Then there should also be a qmp_put() API which calls put_device() to
decrease the refcount.

Ideally, the final refcount should be dropped in qmp_remove() and then
the release callback will be called automatically to free "struct qmp".

> That way if someone unbinds the aoss device, the client will still have
> a "valid" pointer, but won't be able to qmp_send() after qmp_close() has
> been called in the aoss remove function.
> 

How can someone remove the qmp device if a client is holding its reference?

Thanks,
Mani

> Regards,
> Bjorn
> 
> > +	if (!pdev)
> > +		return ERR_PTR(-EINVAL);
> > +
> > +	qmp = platform_get_drvdata(pdev);
> > +	return qmp ? qmp : ERR_PTR(-EPROBE_DEFER);
> > +}
> > +EXPORT_SYMBOL(qmp_get);
> > +
> >  static int qmp_probe(struct platform_device *pdev)
> >  {
> >  	struct resource *res;
> > -- 
> > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> > a Linux Foundation Collaborative Project
> >