RE: [RFC LINUX PATCH 0/3] Allow remote to specify shared memory

[Jiaying Liang]

HI Loic,

> -----Original Message-----
> From: Loic PALLARDY [mailto:loic.pallardy@xxxxxx]
> Sent: Wednesday, March 29, 2017 11:57 AM
> To: Jiaying Liang; Suman Anna; Wendy Liang
> Cc: Bjorn Andersson; linux-remoteproc@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx
> Subject: RE: [RFC LINUX PATCH 0/3] Allow remote to specify shared memory
>
>
>
> > -----Original Message-----
> > From: linux-remoteproc-owner@xxxxxxxxxxxxxxx [mailto:linux-remoteproc-
> > owner@xxxxxxxxxxxxxxx] On Behalf Of Jiaying Liang
> > Sent: Wednesday, March 29, 2017 6:41 PM
> > To: Suman Anna <s-anna@xxxxxx>; Wendy Liang <sunnyliangjy@xxxxxxxxx>
> > Cc: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>; linux-
> > remoteproc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > Subject: RE: [RFC LINUX PATCH 0/3] Allow remote to specify shared
> > memory
> >
> > Hi Suman,
> >
> > > -----Original Message-----
> > > From: Suman Anna [mailto:s-anna@xxxxxx]
> > > Sent: Tuesday, March 28, 2017 4:24 PM
> > > To: Wendy Liang
> > > Cc: Jiaying Liang; Bjorn Andersson;
> > > linux-remoteproc@xxxxxxxxxxxxxxx;
> > > linux- kernel@xxxxxxxxxxxxxxx; Jiaying Liang
> > > Subject: Re: [RFC LINUX PATCH 0/3] Allow remote to specify shared
> > > memory
> > >
> > > Hi Wendy,
> > >
> > > On 03/28/2017 01:52 PM, Wendy Liang wrote:
> > > > Thanks Suman for your comments.
> > > >
> > > > On Mon, Mar 27, 2017 at 8:54 AM, Suman Anna <s-anna@xxxxxx>
> wrote:
> > > >> Hi Wendy,
> > > >>
> > > >> On 03/24/2017 02:22 PM, Wendy Liang wrote:
> > > >>> This patch enables the remoteproc to specify the shared memory.
> > > >>> Remoteproc declared this memory as DMA memory.
> > > >>> It can be used for virtio, or shared buffers.
> > > >>
> > > >> You should be able to achieve this without any remoteproc core
> > changes.
> > > >> You can do this by defining a reserved-memory node in your DTS
> > > >> file (can be a CMA pool or a DMA pool), assigning the node using
> > > >> memory-region in your remoteproc DT node and using the function,
> > > >> of_reserved_mem_device_init() in your remoteproc driver.
> > > >
> > > > The idea to introduce the rproc_mem is to let the remote to
> > > > specify the shared memory.
> > > > I am trying to see if there is a way to specify this software
> > > > attribute without touching the device tree as it doesn't look like
> > > > it is
> > > hardware related.
> > > > And try to see if there is a way that when I change the firmware,
> > > > i don't need to change the device tree.
> > >
> > > So is this shared memory going to be accessed through an MMU by the
> > > remote processor? If not, don't you need a specific carveout, which
> > > would then in turn mean boot-time memory reservation?
> > [Wendy] This memory is not accessed through MMU by remote.
> > Here is the usecase, the number of remotes can be changed at run time,
> > Also the firmware running on the remotes can be changed. And the
> > remote will Need to memory map those memory before it can use it.
> >
> > From what you have suggested, we reserved memory from the device node,
> > and then remoteproc driver linked to that reserved memory with
> > "memory- region", I suppose different remoteproc drivers can share one
> > "memory- region". However, now the question is how the remote knows
> > the shared memory.
> > Let say I use rpmsg for the communication between the two. But how can
> > remote knows about the shared buffers before it can used it.
> >
> > I  saw Loic has a patch to add virtio config to specify this buffer,
> > however, it is not in the latest linux kernel master. And thus, trying
> > to see if there is another way to solve this issue. Use existing
> > carveout to specify this memory?
> Hi Wendy,
>
> Potential issue with this proposal if the order resource table is proceed. This
> memory region should be assigned to device driver first before starting any
> allocation.
[Wendy] User will need to put it to the first entry in the resource table. So that
It can be declared first before device driver to allocate memory.
> Moreover you can assign only one region to a device. But you need different
> memory regions with different attributes: one for firmware and one for vring
> for example.
> That's why we propose sub-dev mechanism some months ago.
[Wendy]  Just in our case, we only use virtio devices. But I agree, there can be
Limitations if you have other sub-devices.

>
> I think we need to find a central mechanism to manage "fixed" memory
> region for firmware (carveout) vring as both are handled by rproc.
> For rpmsg buffer, one proposal will be to assigned a dedicated region to
> vring device as mentioned in "[PATCH v4 0/5] virtio_rpmsg: make rpmsg
> channel configurable" cover letter.
> It will be rproc responsibility to provide this specific memory region based
> either on DT or an firmware resource table information to virtio device.
[Wendy] Just the virtio_rpmsg is not in the latest Linux kernel master. Is there
Any plan to apply the patch?

I agree we need to find a central mechanism to manage "fixed" memory.
Here are some questions:
* Shall we reuse carveout resource for "fixed" memory?
    * Although "fixed" memory doesn't sound like the same as "carveout" memory to me.
       We may consider "fixed" memory as carveout resource with pre-defined addresses. Is this ok?
* How to linked the fixed memory to the target device (e.g. virtio device)?, Can we use "name" of the memory resource?
   * how to "formalize" the name? "virtio_<id>"?

Maybe Bjorn can provide some suggestions on the "fixed" memory solution.

Thanks,
Wendy


>
> Regards,
> Loic
> >
> > Thanks,
> > Wendy
> >
> > >
> > > regards
> > > Suman
> > >
> > > >
> > > > Thanks,
> > > > Wendy
> > > >
> > > >>
> > > >> regards
> > > >> Suman
> > > >>
> > > >>>
> > > >>> Wendy Liang (3):
> > > >>>   remoteproc: add rproc mem resource entry
> > > >>>   remoteproc: add rproc_mem resource entry handler
> > > >>>   remoteproc: Release DMA declare mem when cleanup rsc
> > > >>>
> > > >>>  drivers/remoteproc/remoteproc_core.c | 40
> > > ++++++++++++++++++++++++++++++++++++
> > > >>>  include/linux/remoteproc.h           | 23 ++++++++++++++++++++-
> > > >>>  2 files changed, 62 insertions(+), 1 deletion(-)
> > > >>>
> > > >>
> > > >> --
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> >
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