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Subject: Re: [PATCH 2/2] remoteproc: Fix and restore the parenting hierarchy
 for vdev
To:     Mathieu Poirier <mathieu.poirier@linaro.org>
CC:     Bjorn Andersson <bjorn.andersson@linaro.org>,
        Loic Pallardy <loic.pallardy@st.com>,
        Arnaud Pouliquen <arnaud.pouliquen@st.com>,
        Tero Kristo <t-kristo@ti.com>,
        <linux-remoteproc@vger.kernel.org>, <linux-kernel@vger.kernel.org>
References: <20200305224108.21351-1-s-anna@ti.com>
 <20200305224108.21351-3-s-anna@ti.com> <20200317180530.GA1801@xps15>
From:   Suman Anna <s-anna@ti.com>
Message-ID: <17204b55-2d58-d8cf-e504-6b6969afa987@ti.com>
Date:   Wed, 18 Mar 2020 10:00:50 -0500
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Hi Mathieu,

On 3/17/20 1:05 PM, Mathieu Poirier wrote:
> Hi Suman,
> 
> On Thu, Mar 05, 2020 at 04:41:08PM -0600, Suman Anna wrote:
>> The commit 086d08725d34 ("remoteproc: create vdev subdevice with specific
>> dma memory pool") has introduced a new vdev subdevice for each vdev
>> declared in the firmware resource table and made it as the parent for the
>> created virtio rpmsg devices instead of the previous remoteproc device.
>> This changed the overall parenting hierarchy for the rpmsg devices, which
>> were children of virtio devices, and does not allow the corresponding
>> rpmsg drivers to retrieve the parent rproc device through the
>> rproc_get_by_child() API.
>>
>> Fix this by restoring the remoteproc device as the parent. The new vdev
>> subdevice can continue to inherit the DMA attributes from the remoteproc's
>> parent device (actual platform device).
>>
>> Fixes: 086d08725d34 ("remoteproc: create vdev subdevice with specific dma memory pool")
>> Signed-off-by: Suman Anna <s-anna@ti.com>
>> ---
>>  drivers/remoteproc/remoteproc_core.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/remoteproc/remoteproc_core.c b/drivers/remoteproc/remoteproc_core.c
>> index 097f33e4f1f3..ba18f32bd0c4 100644
>> --- a/drivers/remoteproc/remoteproc_core.c
>> +++ b/drivers/remoteproc/remoteproc_core.c
>> @@ -510,7 +510,7 @@ static int rproc_handle_vdev(struct rproc *rproc, struct fw_rsc_vdev *rsc,
>>  
>>  	/* Initialise vdev subdevice */
>>  	snprintf(name, sizeof(name), "vdev%dbuffer", rvdev->index);
>> -	rvdev->dev.parent = rproc->dev.parent;
>> +	rvdev->dev.parent = &rproc->dev;
> 
> I can see how it would not be possible to retrieve the parent rproc device since
> rvdev->dev.parent was set to be platform device...
> 
> I wonder how the original change didn't blow up sysmon_probe() and potentially
> other out-of-tree users of rproc_get_by_child().  

QCOM code uses SMD transport, and not virtio_rpmsg transport, and the
parent-child relationship is direct rproc subdevices which are added in
their platform drivers directly. This affects only virtio-rpmsg clients.
Please see qcom_add_smd_subdev().

It would be nice to have
> someone from the QCOM team test your patch.
> 
>>  	rvdev->dev.dma_pfn_offset = rproc->dev.parent->dma_pfn_offset;
>>  	rvdev->dev.release = rproc_rvdev_release;
>>  	dev_set_name(&rvdev->dev, "%s#%s", dev_name(rvdev->dev.parent), name);
> 
> Be mindful there might be fallouts from applying this patch since it does change
> the location of the vdev under /sys/device/platform/ .
> 
> Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>

Thanks for the review.

regards
Suman