Message-ID: <6feb3c06-c4bd-4e8b-bd89-c73fae9801d1@collabora.com>
Date: Mon, 17 Feb 2025 15:40:33 +0100
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: CK Hu (胡俊光) <ck.hu@...iatek.com>,
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Subject: Re: [PATCH v6 07/42] drm/mediatek: mtk_dpi: Add support for DPI input
 clock from HDMI

Il 14/02/25 03:09, CK Hu (胡俊光) ha scritto:
> On Tue, 2025-02-11 at 12:33 +0100, AngeloGioacchino Del Regno wrote:
>> External email : Please do not click links or open attachments until you have verified the sender or the content.
>>
>>
>> On some SoCs, like MT8195 and MT8188, the DPI instance that is
>> reserved to the HDMI Transmitter uses a different clock topology.
>>
>> In this case, the DPI is clocked by the HDMI IP, and this outputs
>> its clock to the MM input of dpi_pixel_clk, which is essential to
>> enable register access to the DPI IP.
>>
>> Add a `clocked_by_hdmi` member to struct mtk_dpi_conf, and check
>> it to avoid enabling the DPI clocks in the mediatek-drm internal
>> .start() callback (and avoid disabing in the .stop() component
>> callback): this will make sure that the clock configuration
>> sequence is respected during display pipeline setup by following
>> the bridge ops between DPI and HDMI, where the HDMI driver is
>> expected to enable the clocks in the bridge's pre_enable(), and
>> DPI in the enable() cb.
>>
>> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
>> ---
>>   drivers/gpu/drm/mediatek/mtk_dpi.c | 13 ++++++++++---
>>   1 file changed, 10 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/mediatek/mtk_dpi.c b/drivers/gpu/drm/mediatek/mtk_dpi.c
>> index ad07005ad56e..6493c7e2fae4 100644
>> --- a/drivers/gpu/drm/mediatek/mtk_dpi.c
>> +++ b/drivers/gpu/drm/mediatek/mtk_dpi.c
>> @@ -146,6 +146,8 @@ struct mtk_dpi_factor {
>>    * @input_2p_en_bit: Enable bit of two pixel per round feature
>>    * @pixels_per_iter: Quantity of transferred pixels per iteration.
>>    * @edge_cfg_in_mmsys: If the edge configuration for DPI's output needs to be set in MMSYS.
>> + * @clocked_by_hdmi: HDMI IP outputs clock to dpi_pixel_clk input clock, needed
>> + *                  for DPI registers access.
>>    */
>>   struct mtk_dpi_conf {
>>          const struct mtk_dpi_factor *dpi_factor;
>> @@ -167,6 +169,7 @@ struct mtk_dpi_conf {
>>          u32 input_2p_en_bit;
>>          u32 pixels_per_iter;
>>          bool edge_cfg_in_mmsys;
>> +       bool clocked_by_hdmi;
>>   };
>>
>>   static void mtk_dpi_mask(struct mtk_dpi *dpi, u32 offset, u32 val, u32 mask)
>> @@ -587,7 +590,9 @@ static int mtk_dpi_set_display_mode(struct mtk_dpi *dpi,
>>          struct videomode vm = { 0 };
>>
>>          drm_display_mode_to_videomode(mode, &vm);
>> -       mtk_dpi_set_pixel_clk(dpi, &vm, mode->clock);
>> +
>> +       if (!dpi->conf->clocked_by_hdmi)
>> +               mtk_dpi_set_pixel_clk(dpi, &vm, mode->clock);
>>
>>          dpi_pol.ck_pol = MTK_DPI_POLARITY_FALLING;
>>          dpi_pol.de_pol = MTK_DPI_POLARITY_RISING;
>> @@ -922,14 +927,16 @@ void mtk_dpi_start(struct device *dev)
>>   {
>>          struct mtk_dpi *dpi = dev_get_drvdata(dev);
>>
>> -       mtk_dpi_power_on(dpi);
>> +       if (!dpi->conf->clocked_by_hdmi)
>> +               mtk_dpi_power_on(dpi);
> 
> mtk_dpi_bridge_enable() also call mtk_dpi_power_on().
> Add this checking in mtk_dpi_bridge_enable() also.
> 

That's wanted.

>>   }
>>
>>   void mtk_dpi_stop(struct device *dev)
>>   {
>>          struct mtk_dpi *dpi = dev_get_drvdata(dev);
>>
>> -       mtk_dpi_power_off(dpi);
>> +       if (!dpi->conf->clocked_by_hdmi)
>> +               mtk_dpi_power_off(dpi);
> 
> mtk_dpi_bridge_disable() also call mtk_dpi_power_off().
> Add this checking in mtk_dpi_bridge_disable() also.
> 

That's also wanted.

> Because the clock is from hdmi, I think the clock define in DPI node in device tree should be removed.
> Also change the binding document and let the clock not required in MT8195.

No, because the clock is from HDMI, but there's a gate that needs to be
enabled in order to enable the clock output to the DPI hardware.

The clock being *generated from* HDMI IP doesn't mean that there's no
gate in DPI - and that's the actual problem here that we're solving
with clocked_by_hdmi. We are preventing the clock to be ungated to DPI
while it is wrong or unstable.

I didn't miss any check, all that was on purpose.

Regards,
Angelo

> 
> Regards,
> CK
> 
>>   }
>>
>>   unsigned int mtk_dpi_encoder_index(struct device *dev)
>> --
>> 2.48.1
>>
> 

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