Re: [PATCH 0/8] interconnect: Add imx support via devfreq

["Guido Günther" <agx@sigxcpu.org>]

Hi Martin,
On Thu, Mar 26, 2020 at 02:55:27PM +0100, Martin Kepplinger wrote:
> On 26.03.20 03:16, Leonard Crestez wrote:
> > This series adds interconnect scaling support for imx8m series chips. It uses a
> > per-SOC interconnect provider layered on top of multiple instances of devfreq
> > for scalable nodes along the interconnect.
> > 
> > Existing qcom interconnect providers mostly translate bandwidth requests into
> > firmware calls but equivalent firmware on imx8m is much thinner. Scaling
> > support for individual nodes is implemented as distinct devfreq drivers
> > instead.
> > 
> > The imx interconnect provider doesn't communicate with devfreq directly
> > but rather computes "minimum frequencies" for nodes along the path and
> > creates dev_pm_qos requests.
> > 
> > Since there is no single devicetree node that can represent the
> > "interconnect" the main NOC is picked as the "interconnect provider" and
> > will probe the interconnect platform device if #interconnect-cells is
> > present. This avoids introducing "virtual" devices but it means that DT
> > bindings of main NOC includes properties for both devfreq and
> > interconnect.
> > 
> > Only the ddrc and main noc are scalable right now but more can be added.
> > 
> > Also available on a github branch (with various unrelated changes):
> > 	https://github.com/cdleonard/linux/tree/next
> > Testing currently requires NXP branch of atf+uboot
> > 
> > Martin: I believe you should be able to use this to control DRAM
> > frequency from video by just adding interconnect consumer code to
> > nwl-dsi. Sample code:
> > 	https://github.com/cdleonard/linux/commit/43772762aa5045f1ce5623740f9a4baef988d083
> > 	https://github.com/cdleonard/linux/commit/7b601e981b1f517b5d98b43bde292972ded13086
> > 
> 
> Thanks for updating this series Leonard! A few questions for my
> understanding before trying to test:
> 
> Isn't the ddrc_opp_table missing in these additions to the DT? That's
> what I want to scale after all.
> 
> If I want to keep calling the "request", now icc_set_bw(), in nwl-dsi:
> I'd add an "interconnects" property to the node, but what would be my
> interconnect master? i.e.: interconnects = <&noc master? &noc
> IMX8MQ_ICS_DRAM>; At least it's not obvious to me from
> interconnect/imx/imx8mq.c

The NWL DSI host controller is fed by DCSS or mxsfb so any bandwidth
requirements should (as far as I understand things) go into the display
controller driver since that's what fetches from RAM.
Cheers,
 -- Guido

> 
> the interconnect framework seems to be powerful indeed, but I still need
> to fully wrap my head around it.
> 
> thanks for the help so far,
> 
>                                martin
> 
> 
> > Changes since RFCv6:
> > * Replace scalable-nodes stuff with just a fsl,ddrc property. Future
> > scalable nodes can be added as additional phandles on the NOC
> > * Allow building interconnect drivers as modules
> > * Handle icc_provider_del errors in imx_icc_unregister (like EBUSY).
> > * Rename imx-devfreq to imx-bus, similar to exynos-bus
> > * Explain why imx bus clock enabling is not required
> > * All dependencies accepted (some time ago).
> > Link: https://patchwork.kernel.org/cover/11244421/
> > 
> > Changes since RFCv5:
> > * Replace scanning for interconnect-node-id with explicit
> > scalable-nodes/scalable-node-ids property on NoC.
> > * Now passes make `dtbs_check`
> > * Remove struct imx_icc_provider
> > * Switch to of_icc_xlate_onecell
> > * Use of_find_device_by_node to fetch QoS target, this causes fewer probe
> > deferrals, removes dependency on devfreq API and even allows reloading ddrc
> > module at runtime
> > * Add imx_icc_node_destroy helper
> > * Remove 0/1 on DEFINE_BUS_SLAVE/MASTER which created spurious links
> > Link: https://patchwork.kernel.org/cover/11222015/
> > 
> > Changes since RFCv4:
> > * Drop icc proxy nonsense
> > * Make devfreq driver for NOC probe the ICC driver if
> > #interconnect-cells is present
> > * Move NOC support to interconnect series and rename the node in DT
> > * Add support for all chips at once, differences are not intereseting
> > and there is more community interest for 8mq than 8mm.
> > Link: https://patchwork.kernel.org/cover/11111865/
> > 
> > Changes since RFCv3:
> > * Remove the virtual "icc" node and add devfreq nodes as proxy providers
> > * Fix build on 32-bit arm (reported by kbuilt test robot)
> > * Remove ARCH_MXC_ARM64 (never existed in upstream)
> > * Remove _numlinks, calculate instead
> > * Replace __BUSFREQ_H header guard
> > * Improve commit message and comment spelling
> > * Fix checkpatch issues
> > Link to RFCv3: https://patchwork.kernel.org/cover/11078671/
> > 
> > Changes since RFCv2 and initial work by Alexandre Bailon:
> > * Relying on devfreq and dev_pm_qos instead of CLK
> > * No more "platform opp" stuff
> > * No more special suspend handling: use suspend-opp on devfreq instead
> > * Replace all mentions of "busfreq" with "interconnect"
> > Link to v2: https://patchwork.kernel.org/cover/11021563/
> > 
> > Leonard Crestez (8):
> >   dt-bindings: interconnect: Add bindings for imx8m noc
> >   PM / devfreq: Add generic imx bus scaling driver
> >   PM / devfreq: imx: Register interconnect device
> >   interconnect: Add imx core driver
> >   interconnect: imx: Add platform driver for imx8mm
> >   interconnect: imx: Add platform driver for imx8mq
> >   interconnect: imx: Add platform driver for imx8mn
> >   arm64: dts: imx8m: Add NOC nodes
> > 
> >  .../bindings/interconnect/fsl,imx8m-noc.yaml  | 138 ++++++++
> >  arch/arm64/boot/dts/freescale/imx8mm.dtsi     |  24 ++
> >  arch/arm64/boot/dts/freescale/imx8mn.dtsi     |  24 ++
> >  arch/arm64/boot/dts/freescale/imx8mq.dtsi     |  24 ++
> >  drivers/devfreq/Kconfig                       |   9 +
> >  drivers/devfreq/Makefile                      |   1 +
> >  drivers/devfreq/imx-bus.c                     | 181 +++++++++++
> >  drivers/interconnect/Kconfig                  |   1 +
> >  drivers/interconnect/Makefile                 |   1 +
> >  drivers/interconnect/imx/Kconfig              |  17 +
> >  drivers/interconnect/imx/Makefile             |   9 +
> >  drivers/interconnect/imx/imx.c                | 298 ++++++++++++++++++
> >  drivers/interconnect/imx/imx.h                |  62 ++++
> >  drivers/interconnect/imx/imx8mm.c             | 108 +++++++
> >  drivers/interconnect/imx/imx8mn.c             |  97 ++++++
> >  drivers/interconnect/imx/imx8mq.c             | 106 +++++++
> >  include/dt-bindings/interconnect/imx8mm.h     |  49 +++
> >  include/dt-bindings/interconnect/imx8mn.h     |  41 +++
> >  include/dt-bindings/interconnect/imx8mq.h     |  48 +++
> >  19 files changed, 1238 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/interconnect/fsl,imx8m-noc.yaml
> >  create mode 100644 drivers/devfreq/imx-bus.c
> >  create mode 100644 drivers/interconnect/imx/Kconfig
> >  create mode 100644 drivers/interconnect/imx/Makefile
> >  create mode 100644 drivers/interconnect/imx/imx.c
> >  create mode 100644 drivers/interconnect/imx/imx.h
> >  create mode 100644 drivers/interconnect/imx/imx8mm.c
> >  create mode 100644 drivers/interconnect/imx/imx8mn.c
> >  create mode 100644 drivers/interconnect/imx/imx8mq.c
> >  create mode 100644 include/dt-bindings/interconnect/imx8mm.h
> >  create mode 100644 include/dt-bindings/interconnect/imx8mn.h
> >  create mode 100644 include/dt-bindings/interconnect/imx8mq.h
> > 
> 
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