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Message-ID: <96d90ddd-2910-4419-ba90-64a09a3dbf1e@baylibre.com>
Date: Tue, 16 Apr 2024 16:53:06 +0200
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From: Alexandre Mergnat <amergnat@baylibre.com>
Subject: Re: [PATCH 14/18] drm/mediatek: dpi: add support for dpi clock
To: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Cc: dri-devel@lists.freedesktop.org,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
 Matthias Brugger <matthias.bgg@gmail.com>,
 linux-mediatek@lists.infradead.org, Will Deacon <will@kernel.org>,
 Catalin Marinas <catalin.marinas@arm.com>, devicetree@vger.kernel.org,
 linux-kernel@vger.kernel.org, CK Hu <ck.hu@mediatek.com>,
 Rob Herring <robh+dt@kernel.org>, Daniel Vetter <daniel@ffwll.ch>,
 David Airlie <airlied@gmail.com>, Xinlei Lee <xinlei.lee@mediatek.com>,
 Jitao Shi <jitao.shi@mediatek.com>, linux-arm-kernel@lists.infradead.org,
 linux-pwm@vger.kernel.org, Conor Dooley <conor+dt@kernel.org>,
 Thierry Reding <thierry.reding@gmail.com>,
 Fabien Parent <fparent@baylibre.com>,
 =?UTF-8?Q?Uwe_Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>,
 Chun-Kuang Hu <chunkuang.hu@kernel.org>,
 Philipp Zabel <p.zabel@pengutronix.de>
References: <20231023-display-support-v1-0-5c860ed5c33b@baylibre.com>
 <20231023-display-support-v1-14-5c860ed5c33b@baylibre.com>
 <cf25a3cc-6411-45f5-bc7a-6b69cf28c860@collabora.com>
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On 24/10/2023 11:12, AngeloGioacchino Del Regno wrote:
> Il 23/10/23 16:40, amergnat@baylibre.com ha scritto:
>> From: Fabien Parent <fparent@baylibre.com>
>>
>> MT8365 requires an additional clock for DPI. Add support for that
>> additional clock.
>>
>> Signed-off-by: Fabien Parent <fparent@baylibre.com>
>> Signed-off-by: Alexandre Mergnat <amergnat@baylibre.com>
> 
> I'm not convinced that this is right... at all.
> 
>  From a fast check of the MT8365 DPI clocks, I can see that the DPI0 
> clock declares
> parent VPLL_DPIX (a fixed clock), but nothing ever has VPLL_DPIX_EN 
> (which is the
> GATE clock, enabling output of DPIx VPLL?).
> 
> But then, there's even more: no clock ever references the 
> CLK_TOP_DPI0_SEL nor the
> CLK_TOP_DPI1_SEL gate, which is a PLL parent selector... in other 
> platforms, that
> is muxing through the TVDPLL, but on MT8365 that is LVDSPLL?!

AFAI see into mt8365 documentation, there is no TVDPLL, only LVDSPLL

> 
> I have many questions now:
> * Two PLLs are apparently brought up, but which one is the right one?!
>    * Is the LVDS PLL really used for DisplayPort? (dpi0_sel)

Seems to be LVDS

                                  enable  prepare  protect                                duty  hardware
    clock                          count    count    count        rate   accuracy phase  cycle    enable
-------------------------------------------------------------------------------------------------------
  clk26m                              18       19        1    26000000          0     0         Y
     vpll_dpix                         1        1        0    75000000          0     0  50000         Y
        mm_flvdstx_pxl                 0        0        0    75000000          0     0  50000         N
        mm_dpi0_dpi0                   1        1        0    75000000          0     0  50000         Y
        vpll_dpix_en                   0        0        0    75000000          0     0  50000         N
     lvdspll                           1        1        0   283999497          0     0  50000         Y
        lvdspll_d16                    0        0        0    17749968          0     0  50000         Y
        lvdspll_d8                     0        0        0    35499937          0     0  50000         Y
        lvdspll_d4                     0        0        0    70999874          0     0  50000         Y
        lvdspll_d2                     1        1        0   141999748          0     0  50000         Y
           dpi0_sel                    1        1        0   141999748          0     0  50000         Y
           dpi1_sel                    0        0        0   141999748          0     0  50000         N
     mmpll                             1        1        0   456999909          0     0  50000         Y
        mmpll_ck                       1        1        0   456999909          0     0  50000         Y
           mm_sel                     15       15        0   456999909          0     0  50000         Y
              mm_dpi0                  1        1        0   456999909          0     0  50000         Y


> * Are you sure that CLK_MM_DPI0_DPI0's parent shouldn't be dpi0_sel 
> instead?

I'm agree with you. After few change, it works.

-       GATE_MM0(CLK_MM_DPI0_DPI0, "mm_dpi0_dpi0", "vpll_dpix", 20),
+       GATE_MM0(CLK_MM_DPI0_DPI0, "mm_dpi0_dpi0", "dpi0_sel", 20),

-                       clocks = <&topckgen CLK_TOP_DPI0_SEL>,
+                       clocks = <&mmsys CLK_MM_DPI0_DPI0>,


                                  enable  prepare  protect                                duty  hardware
    clock                          count    count    count        rate   accuracy phase  cycle    enable
-------------------------------------------------------------------------------------------------------
     vpll_dpix                        0       0        0        75000000    0          0     50000      Y
        mm_flvdstx_pxl                0       0        0        75000000    0          0     50000      N
        vpll_dpix_en                  0       0        0        75000000    0          0     50000      N

     lvdspll                          1       1        0        283999497   0          0     50000      Y
        lvdspll_d16                   0       0        0        17749968    0          0     50000      Y
        lvdspll_d8                    0       0        0        35499937    0          0     50000      Y
        lvdspll_d4                    0       0        0        70999874    0          0     50000      Y
        lvdspll_d2                    1       1        0        141999748   0          0     50000      Y
           dpi0_sel                   1       1        0        141999748   0          0     50000      Y
              mm_dpi0_dpi0            1       1        0        141999748   0          0     50000      Y
           dpi1_sel                   0       0        0        141999748   0          0     50000      N

     mmpll                            1       1        0        456999909   0          0     50000      Y
        mmpll_d2                      0       0        0        228499954   0          0     50000      Y
        mmpll_ck                      1       1        0        456999909   0          0     50000      Y
           mm_sel                     15      15       0        456999909   0          0     50000      Y
              mm_dpi0                 1       1        0        456999909   0          0     50000      Y


> * Where is DPI1 in this SoC? Why is there a dpi1_sel clock, but no MM clock
>    for the DPI1 controller? Is there any DPI1 controller, even?!

DPI1 isn't documented.

>    * Why is there a DPI1 MUX, if there's no DPI1 controller?!

Good question, I don't know. Legacy of the downstream code.

That will be fixed for the next version.

-- 
Regards,
Alexandre