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From: Bjorn Andersson <bjorn.andersson@linaro.org>
To: Jeffrey Hugo <jhugo@codeaurora.org>
Cc: Lina Iyer <lina.iyer@linaro.org>,
	Ohad Ben-Cohen <ohad@wizery.com>,
	linux-remoteproc@vger.kernel.org, linux-arm-msm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 00/17] Make rpmsg a framework
Date: Mon, 12 Sep 2016 11:49:57 -0700	[thread overview]
Message-ID: <20160912184957.GI405@tuxbot> (raw)
In-Reply-To: <bc618ac9-13c8-e9bf-c7e9-fe5b7309a585@codeaurora.org>

On Mon 12 Sep 11:13 PDT 2016, Jeffrey Hugo wrote:

> On 9/12/2016 12:00 PM, Bjorn Andersson wrote:
> >On Mon 12 Sep 09:52 PDT 2016, Lina Iyer wrote:
> >
> >>Hi Bjorn,
> >>
> >>On Thu, Sep 01 2016 at 16:28 -0600, Bjorn Andersson wrote:
> >>>This series splits the virtio rpmsg bus driver into a rpmsg bus and a virtio
> >>>backend/wireformat.
> >>>
> >>>
> >>>As we discussed the Qualcomm SMD implementation a couple of years back people
> >>>suggested that I should make it "a rpmsg thingie". With the introduction of the
> >>>Qualcomm 8996 platform, we must support a variant of the communication
> >>>mechanism that share many of the characteristics of SMD, but are different
> >>>enough that it can't be done in a single implementation. As such there is
> >>>enough benefit to do the necessary work and being able to make SMD a "rpmsg
> >>>thingie".
> >>>
> >>>On-top of this series I have patches to switch the current smd clients over to
> >>>rpmsg (and by that drop the existing SMD implementation).
> >>>
> >>>All this allows me to implement the new backend and reuse all existing SMD
> >>>drivers with the new mechanism.
> >>>
> >>
> >>RPM Communication has to supported even when IRQs are disabled. The most
> >>important use of this communication is to set the wake up time for the
> >>CPU subsystem when all the CPUs are powered off.
> >
> >Can you point me to the downstream code where this is implemented so I
> >can have a look? Do you expect to get the response on that request?
> 
> Have a look at -
> smd_mask_receive_interrupt()
> smd_is_pkt_avail()
> 

In msm-3.18 these still seems to only come from either
msm_rpm_enter_sleep() and the rpm-clock driver, related to flushing
cached sleep state requests.

> Every request to the RPM generates a response.  The Linux RPM driver may
> decide to let the response sit in the fifo, or it may need to read and
> process it.
> 

Right, I presume we save some time by not waiting for these responses as
we want to reach sleep as soon as possible. The answer I got last time
this was discussed was that it was an optimization, not a functional
requirement.


I'm not at all against having the rpm driver cache the state
information and the smd driver process read/writes from the rpm driver
in IRQ context. I do however not know how to trigger the flush in a sane
way.

> >
> >>In addition to that,
> >>"sleep" votes that are sent by the application processor subsystem to
> >>allow system to go into deep sleep modes can only be triggered when the
> >>CPU PM domains are power collapsed, drivers do not have a knowledge of
> >>when that happens.
> >
> >Do you mean the actual sleep votes can only be with the CPU PM domains
> >collapsed?
> >
> >It's been a while since I dug through that code, but there was several
> >cases where sleep votes would be sent out during normal execution as
> >well, and then there's the optimization of flushing out all cached sleep
> >votes when we're on the way down.
> >
> >>This has to be done by a platform code that registers
> >>for CPU PM domain power_off/on callbacks.
> >>
> >
> >Ok, sounds like we have a legit use case for improving this.
> >
> >>Using rpmsg may be nice for RPM SMD communication, but mutexes need to
> >>go away for this driver to be any useful than bare bones active mode
> >>resource requests for QCOM SoCs. By not doing that now, we lock
> >>ourselves out of using this SMD driver in the near future when CPU PM
> >>domains are available in the kernel with an ability to do system low
> >>power modes.
> >>
> >
> >The last time I looked at this there where no cases when it was
> >_required_ to support transmitting requests to the rpm from IRQ context.
> 
> I no longer work on SMD, but when I did this was in fact a strict
> requirement.

When I dissected all the users of the API I came to the conclusion that
this requirement (on the SMD driver) came from above mentioned
optimization.

> If I recall correctly, there was a parameter in the RPM driver
> for the transmit function that indicated if the request was being made in
> atomic context or not, which would change the behavior of how the transmit
> was handled.
> 

You're correct, the question is still which of these code paths are
actually needed and to motivate the endless maintenance of the extra
code.


Nice to see you on the mailing list again Jeff.

Regards,
Bjorn

WARNING: multiple messages have this Message-ID (diff)
From: bjorn.andersson@linaro.org (Bjorn Andersson)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2 00/17] Make rpmsg a framework
Date: Mon, 12 Sep 2016 11:49:57 -0700	[thread overview]
Message-ID: <20160912184957.GI405@tuxbot> (raw)
In-Reply-To: <bc618ac9-13c8-e9bf-c7e9-fe5b7309a585@codeaurora.org>

On Mon 12 Sep 11:13 PDT 2016, Jeffrey Hugo wrote:

> On 9/12/2016 12:00 PM, Bjorn Andersson wrote:
> >On Mon 12 Sep 09:52 PDT 2016, Lina Iyer wrote:
> >
> >>Hi Bjorn,
> >>
> >>On Thu, Sep 01 2016 at 16:28 -0600, Bjorn Andersson wrote:
> >>>This series splits the virtio rpmsg bus driver into a rpmsg bus and a virtio
> >>>backend/wireformat.
> >>>
> >>>
> >>>As we discussed the Qualcomm SMD implementation a couple of years back people
> >>>suggested that I should make it "a rpmsg thingie". With the introduction of the
> >>>Qualcomm 8996 platform, we must support a variant of the communication
> >>>mechanism that share many of the characteristics of SMD, but are different
> >>>enough that it can't be done in a single implementation. As such there is
> >>>enough benefit to do the necessary work and being able to make SMD a "rpmsg
> >>>thingie".
> >>>
> >>>On-top of this series I have patches to switch the current smd clients over to
> >>>rpmsg (and by that drop the existing SMD implementation).
> >>>
> >>>All this allows me to implement the new backend and reuse all existing SMD
> >>>drivers with the new mechanism.
> >>>
> >>
> >>RPM Communication has to supported even when IRQs are disabled. The most
> >>important use of this communication is to set the wake up time for the
> >>CPU subsystem when all the CPUs are powered off.
> >
> >Can you point me to the downstream code where this is implemented so I
> >can have a look? Do you expect to get the response on that request?
> 
> Have a look at -
> smd_mask_receive_interrupt()
> smd_is_pkt_avail()
> 

In msm-3.18 these still seems to only come from either
msm_rpm_enter_sleep() and the rpm-clock driver, related to flushing
cached sleep state requests.

> Every request to the RPM generates a response.  The Linux RPM driver may
> decide to let the response sit in the fifo, or it may need to read and
> process it.
> 

Right, I presume we save some time by not waiting for these responses as
we want to reach sleep as soon as possible. The answer I got last time
this was discussed was that it was an optimization, not a functional
requirement.


I'm not at all against having the rpm driver cache the state
information and the smd driver process read/writes from the rpm driver
in IRQ context. I do however not know how to trigger the flush in a sane
way.

> >
> >>In addition to that,
> >>"sleep" votes that are sent by the application processor subsystem to
> >>allow system to go into deep sleep modes can only be triggered when the
> >>CPU PM domains are power collapsed, drivers do not have a knowledge of
> >>when that happens.
> >
> >Do you mean the actual sleep votes can only be with the CPU PM domains
> >collapsed?
> >
> >It's been a while since I dug through that code, but there was several
> >cases where sleep votes would be sent out during normal execution as
> >well, and then there's the optimization of flushing out all cached sleep
> >votes when we're on the way down.
> >
> >>This has to be done by a platform code that registers
> >>for CPU PM domain power_off/on callbacks.
> >>
> >
> >Ok, sounds like we have a legit use case for improving this.
> >
> >>Using rpmsg may be nice for RPM SMD communication, but mutexes need to
> >>go away for this driver to be any useful than bare bones active mode
> >>resource requests for QCOM SoCs. By not doing that now, we lock
> >>ourselves out of using this SMD driver in the near future when CPU PM
> >>domains are available in the kernel with an ability to do system low
> >>power modes.
> >>
> >
> >The last time I looked at this there where no cases when it was
> >_required_ to support transmitting requests to the rpm from IRQ context.
> 
> I no longer work on SMD, but when I did this was in fact a strict
> requirement.

When I dissected all the users of the API I came to the conclusion that
this requirement (on the SMD driver) came from above mentioned
optimization.

> If I recall correctly, there was a parameter in the RPM driver
> for the transmit function that indicated if the request was being made in
> atomic context or not, which would change the behavior of how the transmit
> was handled.
> 

You're correct, the question is still which of these code paths are
actually needed and to motivate the endless maintenance of the extra
code.


Nice to see you on the mailing list again Jeff.

Regards,
Bjorn

  reply	other threads:[~2016-09-12 18:49 UTC|newest]

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-01 22:27 [PATCH v2 00/17] Make rpmsg a framework Bjorn Andersson
2016-09-01 22:27 ` Bjorn Andersson
2016-09-01 22:27 ` [PATCH v2 01/17] rpmsg: Enable matching devices with drivers based on DT Bjorn Andersson
2016-09-01 22:27   ` Bjorn Andersson
2016-09-01 22:27   ` Bjorn Andersson
2016-09-08  1:46   ` spjoshi
2016-09-08  1:46     ` spjoshi at codeaurora.org
2016-09-09  4:30     ` Bjorn Andersson
2016-09-09  4:30       ` Bjorn Andersson
2016-09-09 22:07       ` Sarangdhar Joshi
2016-09-09 22:07         ` Sarangdhar Joshi
2016-09-01 22:27 ` [PATCH v2 02/17] rpmsg: Name rpmsg devices based on channel id Bjorn Andersson
2016-09-01 22:27   ` Bjorn Andersson
2016-09-01 22:27   ` Bjorn Andersson
2016-09-08  1:46   ` spjoshi
2016-09-08  1:46     ` spjoshi at codeaurora.org
2016-09-01 22:27 ` [PATCH v2 03/17] rpmsg: rpmsg_send() operations takes rpmsg_endpoint Bjorn Andersson
2016-09-01 22:27   ` Bjorn Andersson
2016-09-01 22:27 ` [PATCH v2 04/17] rpmsg: Make rpmsg_create_ept() take channel_info struct Bjorn Andersson
2016-09-01 22:27   ` Bjorn Andersson
2016-09-01 22:27   ` Bjorn Andersson
2016-09-01 22:27 ` [PATCH v2 05/17] rpmsg: Clean up rpmsg device vs channel naming Bjorn Andersson
2016-09-01 22:27   ` Bjorn Andersson
2016-09-01 22:27   ` Bjorn Andersson
2016-09-01 22:27 ` [PATCH v2 06/17] rpmsg: Introduce indirection table for rpmsg_device operations Bjorn Andersson
2016-09-01 22:27   ` Bjorn Andersson
2016-09-01 22:27 ` [PATCH v2 07/17] rpmsg: Move rpmsg_device API to new file Bjorn Andersson
2016-09-01 22:27   ` Bjorn Andersson
2016-09-01 22:28 ` [PATCH v2 08/17] rpmsg: Indirection table for rpmsg_endpoint operations Bjorn Andersson
2016-09-01 22:28   ` Bjorn Andersson
2016-09-01 22:28 ` [PATCH v2 09/17] rpmsg: Move endpoint related interface to rpmsg core Bjorn Andersson
2016-09-01 22:28   ` Bjorn Andersson
2016-09-01 22:28 ` [PATCH v2 10/17] rpmsg: Move helper for finding rpmsg devices to core Bjorn Andersson
2016-09-01 22:28   ` Bjorn Andersson
2016-09-01 22:28 ` [PATCH v2 11/17] rpmsg: Split off generic tail of create_channel() Bjorn Andersson
2016-09-01 22:28   ` Bjorn Andersson
2016-09-01 22:28 ` [PATCH v2 12/17] rpmsg: Split rpmsg core and virtio backend Bjorn Andersson
2016-09-01 22:28   ` Bjorn Andersson
2016-09-01 22:28 ` [PATCH v2 13/17] rpmsg: Hide rpmsg indirection tables Bjorn Andersson
2016-09-01 22:28   ` Bjorn Andersson
2016-09-01 22:28 ` [PATCH v2 14/17] rpmsg: virtio: Hide vrp pointer from the public API Bjorn Andersson
2016-09-01 22:28   ` Bjorn Andersson
2016-09-01 22:28 ` [PATCH v2 15/17] rpmsg: Move virtio specifics from public header Bjorn Andersson
2016-09-01 22:28   ` Bjorn Andersson
2016-09-01 22:28 ` [PATCH v2 16/17] rpmsg: Allow callback to return errors Bjorn Andersson
2016-09-01 22:28   ` Bjorn Andersson
2016-09-01 22:28 ` [PATCH v2 17/17] rpmsg: Introduce Qualcomm SMD backend Bjorn Andersson
2016-09-01 22:28   ` Bjorn Andersson
2016-09-12 16:52 ` [PATCH v2 00/17] Make rpmsg a framework Lina Iyer
2016-09-12 16:52   ` Lina Iyer
2016-09-12 18:00   ` Bjorn Andersson
2016-09-12 18:00     ` Bjorn Andersson
2016-09-12 18:13     ` Jeffrey Hugo
2016-09-12 18:13       ` Jeffrey Hugo
2016-09-12 18:49       ` Bjorn Andersson [this message]
2016-09-12 18:49         ` Bjorn Andersson
2016-09-12 19:21         ` Jeffrey Hugo
2016-09-12 19:21           ` Jeffrey Hugo
2016-09-12 19:58           ` Bjorn Andersson
2016-09-12 19:58             ` Bjorn Andersson
2016-09-12 21:36             ` Karthikeyan Ramasubramanian
2016-09-12 21:36               ` Karthikeyan Ramasubramanian
2016-09-12 21:53               ` Bjorn Andersson
2016-09-12 21:53                 ` Bjorn Andersson
2016-09-12 22:22   ` Lina Iyer
2016-09-12 22:22     ` Lina Iyer
2016-09-12 22:58     ` Bjorn Andersson
2016-09-12 22:58       ` Bjorn Andersson

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