Re: [PATCH v8 0/6] arm/arm64: mediatek: Fix mmsys device probing

[Matthias Brugger]

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).

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
>>>>
>>>
>>
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