Re: [PATCH V4 0/4] Add TIOCM Signals support for RPMSG char devices
From: Bjorn Andersson
Date: Tue Oct 09 2018 - 14:27:20 EST
On Tue 09 Oct 09:02 PDT 2018, Arnaud Pouliquen wrote:
> hello Bjorn,
> On 10/08/2018 06:23 PM, Bjorn Andersson wrote:
> > On Mon 08 Oct 06:08 PDT 2018, Arnaud Pouliquen wrote:
> >> Hi Arun, Bjorn,
> >> On 10/08/2018 08:38 AM, Arun Kumar Neelakantam wrote:
> >>> Glink transport support signals to exchange state notification between
> >>> local and remote side clients. Adding support to send/receive the signal
> >>> command and notify the clients through callback and POLL notification.
> >> Please correct me if i'm wrong...My concern here is that this patchset
> >> implements a rpmsg service in the rpmsg core. I would separate this from
> >> the rpmsg core, as this is not part of the rpmsg protocol but seems
> >> linked to the serial protocol itself.
> >> Could it be implemented in rpmsg_char, using a dedicated channel...?
> > rpmsg_char does expose a rpmsg channel (be it virtio, smd or glink) to
> > user space. This patch series add support for invoking TIOCMGET and
> > TIOCMSET on these channels.
> I'm not familiar with this concept, that could explain that i don't
> understand this patchset...
> TIOCMGET and TIOCMSET is related to the serial/console flow control, to
> control remote modem/processor, right?
Correct, using the known tty ioctls for flow control we allow userspace
to communicate flow control information to the rpmsg_char driver.
> it seems be implemented only to support the rpmsg_char ioctl interface.
> When i have a look to the glink code, signal is treated by a message
> sent to remote processor. Therefore it seems that it could be treated as
> a service on top of rpmsg (so treat it in rpmsg_char instead of extend
> the rpmsg protocol to treat it in glink driver).
The glink message is a control message, so it's not possible to pass
this inside a channel. As such it's not possible to solve this entirely
Looking at SMD, this is a set of bits in a per-channel control
structure. So there it's clearer that it's some side-band control
Further more, the rpmsg_char driver just exposes a channel to user
space, it does not care about the data inside. As such it's not possible
to generically extend it to support this with in-band messages.
> > In addition to adding the client side of this to rpmsg_char it provides
> > this support for glink, but the same mechanism exists in smd - while
> > this is not supported (today) by the virtio rpmsg.
> This is my main concern, i would like to be sure that this service is
> not related to specific needs introduced by the rmpsg char implementation:
> In this case this should not be part of the rpmsg core but perhaps some
> ops directly provided to the rpmsg_char on registration
Arun's imminent need is for a user space client that needs to flow
control the incoming data stream. But the possibility of controlling the
incoming flow of data is useful in a number of situations.
> > I'm uncertain of how we could implement this mechanism for virtio rpmsg,
> > given that it as a transport doesn't really have a concept of
> > channels/flows - but it's really useful to have!
> > PS. rpmsg_set_signals() can be called from any rpmsg device to perform
> > flow control of the communication channel.
> For my point of view this patch-set extends the rpmsg protocol to add
> channel flow control.
> Does it make sense to have a flow control in rpmsg protocol?
> if yes, should it be linked to a channel or to the remote processor itself?
Having per-channel flow control particularly useful in scenarios where
one has multiple types of data flowing over a shared underlying FIFO -
such as virtio rpmsg. As this allows these different applications to
limit the data rate without having to use application specific side band
> Extra comment: associated documentation update is missing.
Good catch, we should have a section in Documentation/rpmsg.txt
describing this mechanism.
> > Regards,
> > Bjorn
> >> Regards
> >> Arnaud
> >>> Changes since v1:
> >>> - Split the patches as per functional areas like core, char, glink
> >>> - Add set, clear mask for TIOCMSET
> >>> - Merge the char signal callback and POLLPRI patches
> >>> Changes since v2:
> >>> - Modify the rpmsg_get_signals function prototype
> >>> Changes since v3:
> >>> - Correct the TICOMGET case handling as per new rpmsg_get_signals prototype
> >>> - Update the rpmsg_get_signals function header
> >>> Arun Kumar Neelakantam (4):
> >>> rpmsg: core: Add signal API support
> >>> rpmsg: glink: Add support to handle signals command
> >>> rpmsg: char: Add TIOCMGET/TIOCMSET ioctl support
> >>> rpmsg: char: Add signal callback and POLLPRI support
> >>> drivers/rpmsg/qcom_glink_native.c | 126 ++++++++++++++++++++++++++++++++++++++
> >>> drivers/rpmsg/rpmsg_char.c | 74 +++++++++++++++++++++-
> >>> drivers/rpmsg/rpmsg_core.c | 41 +++++++++++++
> >>> drivers/rpmsg/rpmsg_internal.h | 5 ++
> >>> include/linux/rpmsg.h | 26 ++++++++
> >>> 5 files changed, 269 insertions(+), 3 deletions(-)