Date:   Fri, 21 Feb 2020 19:11:58 +0800
From:   CK Hu <ck.hu@...iatek.com>
To:     Matthias Brugger <mbrugger@...e.com>
CC:     Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        <mark.rutland@....com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        "Minghsiu Tsai" <minghsiu.tsai@...iatek.com>,
        Andrew-CT Chen <andrew-ct.chen@...iatek.com>,
        <airlied@...ux.ie>, <mturquette@...libre.com>,
        <dri-devel@...ts.freedesktop.org>,
        Richard Fontana <rfontana@...hat.com>,
        <laurent.pinchart@...asonboard.com>,
        <ulrich.hecht+renesas@...il.com>,
        Collabora Kernel ML <kernel@...labora.com>,
        <linux-clk@...r.kernel.org>,
        Nicolas Boichat <drinkcat@...omium.org>,
        Weiyi Lu <weiyi.lu@...iatek.com>,
        Krzysztof Kozlowski <krzk@...nel.org>, <wens@...e.org>,
        Allison Randal <allison@...utok.net>,
        mtk01761 <wendell.lin@...iatek.com>,
        Owen Chen <owen.chen@...iatek.com>,
        <linux-media@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <p.zabel@...gutronix.de>, <frank-w@...lic-files.de>,
        Seiya Wang <seiya.wang@...iatek.com>, <sean.wang@...iatek.com>,
        Houlong Wei <houlong.wei@...iatek.com>, <robh+dt@...nel.org>,
        <linux-mediatek@...ts.infradead.org>, <hsinyi@...omium.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        Fabien Parent <fparent@...libre.com>, <sboyd@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <rdunlap@...radead.org>, <linux-kernel@...r.kernel.org>,
        Daniel Vetter <daniel@...ll.ch>, <matthias.bgg@...nel.org>
Subject: Re: [PATCH v8 0/6] arm/arm64: mediatek: Fix mmsys device probing

Hi, Matthias:

On Fri, 2020-02-21 at 11:24 +0100, Matthias Brugger wrote:
> 
> On 21/02/2020 10:27, CK Hu wrote:
> > Hi, Enric:
> > 
> > On Fri, 2020-02-21 at 09:56 +0100, Enric Balletbo i Serra wrote:
> >> Hi CK,
> >>
> >> Thanks for your quick answer.
> >>
> >> On 21/2/20 5:39, CK Hu wrote:
> >>> Hi, Enric:
> >>>
> >>> On Thu, 2020-02-20 at 18:21 +0100, Enric Balletbo i Serra wrote:
> >>>> Dear all,
> >>>>
> >>>> Those patches are intended to solve an old standing issue on some
> >>>> Mediatek devices (mt8173, mt2701 and mt2712) in a slightly different way
> >>>> to the precedent series.
> >>>>
> >>>> Up to now both drivers, clock and drm are probed with the same device tree
> >>>> compatible. But only the first driver get probed, which in effect breaks
> >>>> graphics on those devices.
> >>>>
> >>>> The version eight of the series tries to solve the problem with a
> >>>> different approach than the previous series but similar to how is solved
> >>>> on other Mediatek devices.
> >>>>
> >>>> The MMSYS (Multimedia subsystem) in Mediatek SoCs has some registers to
> >>>> control clock gates (which is used in the clk driver) and some registers
> >>>> to set the routing and enable the differnet blocks of the display
> >>>> and MDP (Media Data Path) subsystem. On this series the clk driver is
> >>>> not a pure clock controller but a system controller that can provide
> >>>> access to the shared registers between the different drivers that need
> >>>> it (mediatek-drm and mediatek-mdp). And the biggest change is, that in
> >>>> this version, clk driver is the entry point (parent) which will trigger
> >>>> the probe of the corresponding mediatek-drm driver and pass its MMSYS
> >>>> platform data for display configuration.
> >>>
> >>> When mmsys is a system controller, I prefer to place mmsys in
> >>> drivers/soc/mediatek, and it share registers for clock, display, and mdp
> >>> driver. This means the probe function is placed in
> >>> drivers/soc/mediatek ,its display clock function, mdp clock function are
> >>> placed in drivers/clk, display routing are placed in drivers/gpu/drm,
> >>> and mdp routing are placed in dirvers/video.
> >>>
> >>
> >> I understand what you mean but I am not sure this makes the code clearer and
> >> useful. The driver in drivers/soc/mediatek will be a simple dummy implementation
> >> of a "simple-mfd" device (a driver that simply matches with
> >> "mediatek,mt8173-mmsys" and instantiates the "clk-mt8173-mm" and the
> >> "mediatek-drm" driver (note that mediatek-mdp" is already instantiated via
> >> device-tree).
> >>
> > 
> > It's clear that mmsys is neither a pure clock controller nor a pure
> > routing controller for display and mdp. 
> > 
> >> It'd be nice had a proper device-tree with a "simple-mfd" for mmsys from the
> >> beginning representing how really hardwware is, but I think that, change this
> >> now, will break backward compatibility.
> > 
> > Maybe this is a solution. Current device tree would work only on old
> > kernel version with a bug, so this mean there is no any device tree
> > works on kernel version without bug. Why do we compatible with such
> > device tree?
> > 
> 
> The idea behind this is, that the device-tree could be passed by some boot
> firmware, so that the OS do not care about it. For this we need a stable DTS as
> otherwise newer kernel with older FW would break.
> 
> DTS is supposed to be just a different description of the HW like ACPI. So it
> has to be compatible (newer kernel with older DTS and if possible vice versa).

In my view, there is no FW (except some bug-inside FW) which works on
this dts, so this dts is in a initial state. I think the compatibility
is based on that dts correctly describe the HW. If we find this dts does
not correctly describe the HW and it's in a initial state, should we
still make it compatible?

If you have better solution, just let's forget this.

Regards,
CK

> 
> Regards,
> Matthias
> 
> > Regards,
> > CK
> > 
> >>
> >> IMHO I think that considering the clk driver as entry point is fine, but this is
> >> something that the clock maintainers should decide.
> >>
> >> Also note that this is not only a MT8173 problem I am seeing the same problem on
> >> all other Mediatek SoCs.
> >>
> >> Thanks.
> >>
> >>> Regards,
> >>> CK
> >>>
> >>>>
> >>>> All this series was tested on the Acer R13 Chromebook only.
> >>>>
> >>>> For reference, here are the links to the old discussions:
> >>>>
> >>>> * v7: https://patchwork.kernel.org/project/linux-mediatek/list/?series=241217
> >>>> * v6: https://patchwork.kernel.org/project/linux-mediatek/list/?series=213219
> >>>> * v5: https://patchwork.kernel.org/project/linux-mediatek/list/?series=44063
> >>>> * v4:
> >>>>   * https://patchwork.kernel.org/patch/10530871/
> >>>>   * https://patchwork.kernel.org/patch/10530883/
> >>>>   * https://patchwork.kernel.org/patch/10530885/
> >>>>   * https://patchwork.kernel.org/patch/10530911/
> >>>>   * https://patchwork.kernel.org/patch/10530913/
> >>>> * v3:
> >>>>   * https://patchwork.kernel.org/patch/10367857/
> >>>>   * https://patchwork.kernel.org/patch/10367861/
> >>>>   * https://patchwork.kernel.org/patch/10367877/
> >>>>   * https://patchwork.kernel.org/patch/10367875/
> >>>>   * https://patchwork.kernel.org/patch/10367885/
> >>>>   * https://patchwork.kernel.org/patch/10367883/
> >>>>   * https://patchwork.kernel.org/patch/10367889/
> >>>>   * https://patchwork.kernel.org/patch/10367907/
> >>>>   * https://patchwork.kernel.org/patch/10367909/
> >>>>   * https://patchwork.kernel.org/patch/10367905/
> >>>> * v2: No relevant discussion, see v3
> >>>> * v1:
> >>>>   * https://patchwork.kernel.org/patch/10016497/
> >>>>   * https://patchwork.kernel.org/patch/10016499/
> >>>>   * https://patchwork.kernel.org/patch/10016505/
> >>>>   * https://patchwork.kernel.org/patch/10016507/
> >>>>
> >>>> Best regards,
> >>>>  Enric
> >>>>
> >>>> Changes in v8:
> >>>> - Be a builtin_platform_driver like other mediatek mmsys drivers.
> >>>> - New patches introduced in this series.
> >>>>
> >>>> Changes in v7:
> >>>> - Add R-by from CK
> >>>> - Add R-by from CK
> >>>> - Fix check of return value of of_clk_get
> >>>> - Fix identation
> >>>> - Free clk_data->clks as well
> >>>> - Get rid of private data structure
> >>>>
> >>>> Enric Balletbo i Serra (2):
> >>>>   drm/mediatek: Move MMSYS configuration to include/linux/platform_data
> >>>>   clk/drm: mediatek: Fix mediatek-drm device probing
> >>>>
> >>>> Matthias Brugger (4):
> >>>>   drm/mediatek: Use regmap for register access
> >>>>   drm/mediatek: Omit warning on probe defers
> >>>>   media: mtk-mdp: Check return value of of_clk_get
> >>>>   clk: mediatek: mt8173: Switch MMSYS to platform driver
> >>>>
> >>>>  drivers/clk/mediatek/Kconfig                  |   6 +
> >>>>  drivers/clk/mediatek/Makefile                 |   1 +
> >>>>  drivers/clk/mediatek/clk-mt2701-mm.c          |  30 +++
> >>>>  drivers/clk/mediatek/clk-mt2712-mm.c          |  44 +++++
> >>>>  drivers/clk/mediatek/clk-mt8173-mm.c          | 172 ++++++++++++++++++
> >>>>  drivers/clk/mediatek/clk-mt8173.c             | 104 -----------
> >>>>  drivers/gpu/drm/mediatek/mtk_disp_color.c     |   5 +-
> >>>>  drivers/gpu/drm/mediatek/mtk_disp_ovl.c       |   5 +-
> >>>>  drivers/gpu/drm/mediatek/mtk_disp_rdma.c      |   5 +-
> >>>>  drivers/gpu/drm/mediatek/mtk_dpi.c            |  12 +-
> >>>>  drivers/gpu/drm/mediatek/mtk_drm_crtc.c       |   4 +-
> >>>>  drivers/gpu/drm/mediatek/mtk_drm_ddp.c        |  53 +++---
> >>>>  drivers/gpu/drm/mediatek/mtk_drm_ddp.h        |   4 +-
> >>>>  drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.h   |  56 +-----
> >>>>  drivers/gpu/drm/mediatek/mtk_drm_drv.c        | 113 +-----------
> >>>>  drivers/gpu/drm/mediatek/mtk_drm_drv.h        |  13 +-
> >>>>  drivers/gpu/drm/mediatek/mtk_dsi.c            |   8 +-
> >>>>  drivers/gpu/drm/mediatek/mtk_hdmi.c           |   4 +-
> >>>>  drivers/media/platform/mtk-mdp/mtk_mdp_comp.c |   6 +
> >>>>  include/linux/platform_data/mtk_mmsys.h       |  73 ++++++++
> >>>>  20 files changed, 401 insertions(+), 317 deletions(-)
> >>>>  create mode 100644 drivers/clk/mediatek/clk-mt8173-mm.c
> >>>>  create mode 100644 include/linux/platform_data/mtk_mmsys.h
> >>>>
> >>>
> >>
> >> _______________________________________________
> >> Linux-mediatek mailing list
> >> Linux-mediatek@...ts.infradead.org
> >> http://lists.infradead.org/mailman/listinfo/linux-mediatek
> > 
> 
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