linux-kernel - Re: [PATCH 1/3] soc: qcom: Introduce Protection Domain Restart helpers

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Date:   Tue, 19 Nov 2019 15:17:40 -0800
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     sibis@...eaurora.org
Cc:     srinivas.kandagatla@...aro.org, robh+dt@...nel.org,
        tsoni@...eaurora.org, agross@...nel.org, mark.rutland@....com,
        linux-arm-msm@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        rnayak@...eaurora.org
Subject: Re: [PATCH 1/3] soc: qcom: Introduce Protection Domain Restart
 helpers

On Tue 19 Nov 02:18 PST 2019, sibis@...eaurora.org wrote:

> Hey Bjorn,
> Thanks for taking the time to
> review the series :)
> 
> On 2019-11-19 12:10, Bjorn Andersson wrote:
> > On Mon 18 Nov 06:27 PST 2019, Sibi Sankar wrote:
> > > diff --git a/drivers/soc/qcom/pdr_interface.c
> > > b/drivers/soc/qcom/pdr_interface.c
> > [..]
> > > +static void pdr_indack_work(struct work_struct *work)
> > > +{
> > > +	struct pdr_handle *pdr = container_of(work, struct pdr_handle,
> > > +					      indack_work);
> > > +	struct pdr_list_node *ind, *tmp;
> > > +	struct pdr_service *pds;
> > > +
> > > +	list_for_each_entry_safe(ind, tmp, &pdr->indack_list, node) {
> > > +		pds = ind->pds;
> > > +		pdr_send_indack_msg(pdr, pds, ind->transaction_id);
> > 
> > So when we et a ind_cb with the new status, we need to send an ack
> > request, which will result in a response, just to confirm that we got
> > the event?
> > 
> > Seems like we should fix the qmi code to make it possible to send a
> > request from the indication handler and then we could simply ignore the
> 
> yeah maybe having a provision to send custom requests back on
> indication would be the way to go. Not all indication need to be
> services with requests.
> 

Let's put this on the todo list.

> > response. Or do we need to not pdr->status() until we get the response
> > for some reason?
> 
> adsp waits on the ack response for a fixed duration and seems to throw
> a fatal err is the ack is not serviced. Hence holding back pd->status
> till we service the ack here.
> 

You mean to ensure that someone sleeping in pd->status() doesn't delay
that until its too late?

[..]
> > > +int pdr_handle_init(struct pdr_handle *pdr,
> > > +		    int (*status)(struct pdr_handle *pdr,
> > > +				  struct pdr_service *pds))
> > > +{
> > [..]
> > > +	pdr->servreg_wq = create_singlethread_workqueue("pdr_servreg_wq");
> > > +	if (!pdr->servreg_wq)
> > > +		return -ENOMEM;
> > > +
> > > +	pdr->indack_wq = alloc_ordered_workqueue("pdr_indack_wq",
> > > WQ_HIGHPRI);
> > 
> > The two workqueues means that we should be able to call pdr->status()
> > rom two concurrent contexts, I don't think our clients will expect that.
> > 
> 
> would creating another ordered wq to relay all the pd->status make
> sense?
> 

I would prefer less work queues ;) But I presume you split out the
indack_wq in order to improve the likelihood of meeting the latency
requirements of the remote side.

Perhaps just wrap the status() calls with a status-mutex and then remove
that by reworking the QMI interface to allow us to remove the indack
work?

Regards,
Bjorn