linux-kernel - Re: [PATCH v7 2/6] drm/mediatek: dsi: Improves the DSI lane setup robustness

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Message-ID: <79477810-00a9-47f1-8282-f8077ea082bb@baylibre.com>
Date: Mon, 17 Feb 2025 16:03:20 +0100
From: Alexandre Mergnat <amergnat@...libre.com>
To: CK Hu (胡俊光) <ck.hu@...iatek.com>
Cc: "maarten.lankhorst@...ux.intel.com" <maarten.lankhorst@...ux.intel.com>,
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Subject: Re: [PATCH v7 2/6] drm/mediatek: dsi: Improves the DSI lane setup
 robustness

Hi CK.

On 17/02/2025 08:56, CK Hu (胡俊光) wrote:
> On Fri, 2025-01-10 at 14:31 +0100, Alexandre Mergnat wrote:
>> External email : Please do not click links or open attachments until you have verified the sender or the content.
>> 
>> 
>> Currently, mtk_dsi_lane_ready (which setup the DSI lane) is triggered
>> before mtk_dsi_poweron. lanes_ready flag toggle to true during
>> mtk_dsi_lane_ready function, and the DSI module is set up during
>> mtk_dsi_poweron.
>> 
>> Later, during panel driver init, mtk_dsi_lane_ready is triggered but does
>> nothing because lanes are considered ready. Unfortunately, when the panel
>> driver try to communicate, the DSI returns a timeout.
>> 
>> The solution found here is to put lanes_ready flag to false after the DSI
>> module setup into mtk_dsi_poweron to init the DSI lanes after the power /
>> setup of the DSI module.
> 
> I'm not clear about what happen.
> I think this DSI flow has worked for a long time.
> So only some panel has problem?

I don't know if it's related to a specific panel or not.

> 
> And another question.
> Do you mean mtk_dsi_lane_ready() do some setting to hardware, but lane is not actually ready?

The workflow should be:
... | dsi->lanes_ready = false | Power-on | setup dsi lanes | dsi->lanes_ready = true (to avoid 
re-do dsi lanes setup) | ...

I observe (print function name called + dsi->lanes_ready value):

[    9.086030] mtk_dsi_probe 0
[    9.662319] mtk_dsi_host_attach 0
[    9.662941] mtk_dsi_encoder_init
[    9.984685] mtk_dsi_poweron 0
[   10.043755] mtk_dsi_host_transfer 0
[   10.043769] mtk_dsi_lane_ready 0
[   10.055837] mtk_dsi_host_transfer 1
[   10.055853] mtk_dsi_lane_ready 1
[   10.179788] mtk_dsi_host_transfer 1
[   10.179803] mtk_dsi_lane_ready 1
[   10.179880] mtk_dsi_host_transfer 1
[   10.179885] mtk_dsi_lane_ready 1
[   10.179920] mtk_dsi_host_transfer 1
[   10.179923] mtk_dsi_lane_ready 1
[   10.179986] mtk_dsi_host_transfer 1
[   10.179993] mtk_dsi_lane_ready 1
[   10.180134] mtk_dsi_host_transfer 1
[   10.180143] mtk_dsi_lane_ready 1
[   10.180175] mtk_dsi_host_transfer 1
[   10.180178] mtk_dsi_lane_ready 1
[   10.180223] mtk_dsi_host_transfer 1
[   10.180226] mtk_dsi_lane_ready 1
[   10.180245] mtk_dsi_host_transfer 1
[   10.180248] mtk_dsi_lane_ready 1
[   10.180278] mtk_dsi_host_transfer 1
[   10.180280] mtk_dsi_lane_ready 1
[   10.180312] mtk_dsi_host_transfer 1
[   10.180314] mtk_dsi_lane_ready 1
[   10.203774] mtk_dsi_bridge_atomic_pre_enable
[   10.203787] mtk_dsi_poweron 1
[   10.203793] mtk_output_dsi_enable
[   10.203795] mtk_dsi_lane_ready 1
[   10.471517] mtk_dsi_host_transfer 1
[   10.486962] mtk_dsi_lane_ready 1
[   10.487244] mtk_dsi_host_transfer 1
[   10.503733] mtk_dsi_lane_ready 1

Here the mtk_dsi_lane_ready function:

	static void mtk_dsi_lane_ready(struct mtk_dsi *dsi)
	{
		if (!dsi->lanes_ready) {
			dsi->lanes_ready = true;
			mtk_dsi_rxtx_control(dsi);
			usleep_range(30, 100);
			mtk_dsi_reset_dphy(dsi);
			mtk_dsi_clk_ulp_mode_leave(dsi);
			mtk_dsi_lane0_ulp_mode_leave(dsi);
			mtk_dsi_clk_hs_mode(dsi, 0);
			usleep_range(1000, 3000);
			/* The reaction time after pulling up the mipi signal for dsi_rx */
		}
	}


As you can see, something call "mtk_dsi_bridge_atomic_pre_enable" then mtk_dsi_poweron is called a 
second time. This issue is probably due to the probe order (race condition).
After all, IMHO, after a poweron, the registers status should be consider as unknown (or at least HW 
default value), so, lanes setup has to be done. This solution improve the driver's robustness.


> Or mtk_dsi_lane_ready() configure the hardware and lane is is actually ready,
> but something make it not ready again, what's the thing which break lane ready?
> 
> If this is a bug fix, add Fixes tag.
> 
> Regards,
> CK
> 
>> 
>> Signed-off-by: Alexandre Mergnat <amergnat@...libre.com>
>> ---
>>  drivers/gpu/drm/mediatek/mtk_dsi.c | 2 ++
>>  1 file changed, 2 insertions(+)
>> 
>> diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c b/drivers/gpu/drm/mediatek/mtk_dsi.c
>> index e61b9bc68e9a..dcf0d93881b5 100644
>> --- a/drivers/gpu/drm/mediatek/mtk_dsi.c
>> +++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
>> @@ -724,6 +724,8 @@ static int mtk_dsi_poweron(struct mtk_dsi *dsi)
>>         mtk_dsi_config_vdo_timing(dsi);
>>         mtk_dsi_set_interrupt_enable(dsi);
>> 
>> +       dsi->lanes_ready = false;
>> +
>>         return 0;
>>  err_disable_engine_clk:
>>         clk_disable_unprepare(dsi->engine_clk);
>> 
>> --
>> 2.25.1
>> 
> 
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-- 
Regards,
Alexandre