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Date:   Fri, 17 Jan 2020 15:52:17 -0700
From:   Mathieu Poirier <mathieu.poirier@linaro.org>
To:     =?iso-8859-1?Q?Cl=E9ment?= Leger <cleger@kalray.eu>
Cc:     Arnaud Pouliquen <arnaud.pouliquen@st.com>,
        Ohad Ben-Cohen <ohad@wizery.com>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        linux-remoteproc <linux-remoteproc@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] remoteproc: Add support for predefined notifyids
Message-ID: <20200117225217.GA27535@xps15>
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Hey guys,

On Wed, Jan 15, 2020 at 04:11:03PM +0100, Cl?ment Leger wrote:
> 
> 
> ----- On 15 Jan, 2020, at 16:09, Arnaud Pouliquen arnaud.pouliquen@st.com wrote:
> 
> > On 1/15/20 3:28 PM, Cl?ment Leger wrote:
> >> Hi Arnaud,
> >> 
> >> ----- On 15 Jan, 2020, at 15:06, Arnaud Pouliquen arnaud.pouliquen@st.com wrote:
> >> 
> >>> Hi Cl?ment,
> >>>
> >>> On 1/15/20 11:21 AM, Clement Leger wrote:
> >>>> In order to support preallocated notify ids, if their value is
> >>>> equal to FW_RSC_NOTIFY_ID_ANY, then do no allocate a notify id
> >>>> dynamically but try to allocate the requested one. This is useful when
> >>>> using custom ids to bind them to custom vendor resources. For instance,
> >>>> it allow to assign a group of queues to a specific interrupti in order
> >>>> to dispatch notifications.
> >>>>
> >>>> Signed-off-by: Clement Leger <cleger@kalray.eu>
> >>>> ---
> >>>>  drivers/remoteproc/remoteproc_core.c | 27 +++++++++++++++++++--------
> >>>>  include/linux/remoteproc.h           |  1 +
> >>>>  2 files changed, 20 insertions(+), 8 deletions(-)
> >>>>
> >>>> diff --git a/drivers/remoteproc/remoteproc_core.c
> >>>> b/drivers/remoteproc/remoteproc_core.c
> >>>> index 307df98347ba..b1485fcd0f11 100644
> >>>> --- a/drivers/remoteproc/remoteproc_core.c
> >>>> +++ b/drivers/remoteproc/remoteproc_core.c
> >>>> @@ -351,14 +351,27 @@ int rproc_alloc_vring(struct rproc_vdev *rvdev, int i)
> >>>>  	/*
> >>>>  	 * Assign an rproc-wide unique index for this vring
> >>>>  	 * TODO: assign a notifyid for rvdev updates as well
> >>>> -	 * TODO: support predefined notifyids (via resource table)
> >>>>  	 */
> >>>> -	ret = idr_alloc(&rproc->notifyids, rvring, 0, 0, GFP_KERNEL);
> >>>> -	if (ret < 0) {
> >>>> -		dev_err(dev, "idr_alloc failed: %d\n", ret);
> >>>> -		return ret;
> >>>> +	if (rsc->vring[i].notifyid == FW_RSC_NOTIFY_ID_ANY) {
> >>>> +		ret = idr_alloc(&rproc->notifyids, rvring, 0, 0, GFP_KERNEL);
> >>>> +		if (ret < 0) {
> >>>> +			dev_err(dev, "idr_alloc failed: %d\n", ret);
> >>>> +			return ret;
> >>>> +		}
> >>>> +		notifyid = ret;
> >>>> +
> >>>> +		/* Let the rproc know the notifyid of this vring.*/
> >>>> +		rsc->vring[i].notifyid = notifyid;
> >>>> +	} else {
> >>>> +		/* Reserve requested notify_id */
> >>>> +		notifyid = rsc->vring[i].notifyid;
> >>>> +		ret = idr_alloc(&rproc->notifyids, rvring, notifyid,
> >>>> +				notifyid + 1, GFP_KERNEL);
> >>>> +		if (ret < 0) {
> >>>> +			dev_err(dev, "idr_alloc failed: %d\n", ret);
> >>>> +			return ret;
> >>>> +		}
> >>>>  	}
> >>>> -	notifyid = ret;
> >>>>  
> >>>>  	/* Potentially bump max_notifyid */
> >>>>  	if (notifyid > rproc->max_notifyid)
> >>>> @@ -366,8 +379,6 @@ int rproc_alloc_vring(struct rproc_vdev *rvdev, int i)
> >>>>  
> >>>>  	rvring->notifyid = notifyid;
> >>>>  
> >>>> -	/* Let the rproc know the notifyid of this vring.*/
> >>>> -	rsc->vring[i].notifyid = notifyid;
> >>>>  	return 0;
> >>>>  }
> >>> The rproc_free_vring function resets the notifyid to -1 on free.
> >>> This could generate a side effect if the resource table is not reloaded.
> >> 
> >> Oh indeed, I did not thought of that. What would you recommend ?
> >> If using -1 in free vring, notify ids will be reallocated at next
> >> round.
> > Regarding the code i'm not sure that it is useful to reset the notifyID to -1 on
> > free.

I'm not sure setting notifyid to -1 in rproc_free_vring() is such a big problem.
No matter the code path I look at, if rproc_free_vring() is called something
serious has happened and the resource table will be reloaded if another attempt
at booting the remote processor is done.  It can also be that a graceful
shutdown is underway, in which case the resource table will be reloaded anyway
if/when the slave is brought back in service.

Let me know if I'm missing a scenario.

To me the real problem is if a FW image has set the notifyids in the resource
table to 0xffffffff, thinking they will be overwritten.  In that case things
will really south. 

> > In current version, on alloc, the notifyID is overwriten without check.
> > And as vdev status is updated, vring struct in resource table should be
> > considered as invalid
> > Except if i missed a usecase/race condition...
> > 
> >> 
> >> I was also worried that it would break some existing user applications
> >> which uses "0" as a notify id in vring but expect the id to be
> >> allocated dynamically. With my modification, it means it will try to
> >> use "0" as a predefined id, leading to allocation failure.

From my point of view they will have been lucky for all this time.  Even with
a new version of the resource table (which I think is the right way go)
cases like this will break.

Thanks,
Mathieu

> >> 
> > Yes this could introduce regression for firmware that sets 0 as default value.
> > Probably better to introduce this patch with a new version of the resource table
> > :)
> 
> Understood ;)
> 
> Regards,
> 
> Cl?ment
> 
> > 
> > Regards
> > Arnaud
> >>>
> >>>>  
> >>>> diff --git a/include/linux/remoteproc.h b/include/linux/remoteproc.h
> >>>> index 16ad66683ad0..dcae3394243e 100644
> >>>> --- a/include/linux/remoteproc.h
> >>>> +++ b/include/linux/remoteproc.h
> >>>> @@ -123,6 +123,7 @@ enum fw_resource_type {
> >>>>  };
> >>>>  
> >>>>  #define FW_RSC_ADDR_ANY (-1)
> >>>> +#define FW_RSC_NOTIFY_ID_ANY (-1)This define can also be used in
> >>>> rproc_free_vring
> >> 
> >> Indeed.
> >> 
> >> Thanks for your review.
> >> 
> >> Regards,
> >> 
> >> Cl?ment
> >> 
> >>>
> >>> Regards,
> >>> Arnaud
> >>>>  
> >>>>  /**
> > >>>   * struct fw_rsc_carveout - physically contiguous memory request