linux-kernel - Re: [PATCH] drm/tidss: Decouple max_pclk from tidss feats to remove clock dependency

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Message-ID: <d0854272-fe5e-4977-8526-03a980b348f3@ti.com>
Date: Wed, 18 Jun 2025 14:52:09 +0530
From: Jayesh Choudhary <j-choudhary@...com>
To: <jyri.sarha@....fi>, <dri-devel@...ts.freedesktop.org>, <devarsht@...com>,
        <tomi.valkeinen@...asonboard.com>
CC: <maarten.lankhorst@...ux.intel.com>, <mripard@...nel.org>,
        <tzimmermann@...e.de>, <airlied@...il.com>, <simona@...ll.ch>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/tidss: Decouple max_pclk from tidss feats to remove
 clock dependency



On 18/06/25 13:28, Jayesh Choudhary wrote:
> TIDSS hardware by itself does not have variable max_pclk for each VP.
> Each VP supports a fixed maximum pixel clock. K2 devices and AM62*
> devices uses "ultra-light" version where each VP supports a max of
> 300MHz whereas J7* devices uses TIDSS where all VP can support a
> max pclk of 600MHz.
> The limitation that has been modeled till now comes from the clock
> (PLL can only be programmed to a particular max value). Due to this
> we end up using different compatible for each SoC when the clocking
> architecture changes for VPs, even when the hardware is essentially
> the same.
> max_pclk cannot be entirely removed since the display controller
> should tell if a particular mode clock can be supported or not in crtc's
> "mode_valid()" call. So remove "max_pclk_khz" from the static display
> feat and add it to "tidss_device" structure which would be modified in
> runtime. In mode_valid() call, check if a best frequency match for mode
> clock can be found or not using "clk_round_rate()". Based on that,
> propagate "max_pclk" and check max_clk again only if the requested mode
> clock is greater than saved value. (As the preferred display mode is
> usually the max resolution, driver ends up checking the maximum clock
> the first time itself which is used in subsequent checks)
> Since TIDSS display controller provides clock tolerance of 5%, we use
> this while checking the max_pclk. Also, move up "dispc_pclk_diff()"
> before it is called.
> 
> This will make the existing compatibles reusable.
> 
> Signed-off-by: Jayesh Choudhary <j-choudhary@...com>
> ---
> 
> Test log on TI's J784S4 SoC with a couple of downstream patches
> to integrate DSI support on one of the video ports:
> <https://gist.github.com/Jayesh2000/ad4ab87028740efa60e5eb83fb892097>
> 

Hello All,

Just noticed that the downstream patches that I used for DSI for testing
were applied before this patch in my tree due to which this patch does
not apply cleanly on the linux-next tree.

Apologies for that. I am rolling v2 ASAP.

Jayesh

>  From the logs, we can see that for CLK ID 218 (DSS), we do not have to
> call sci_clk_determine_rate() multiple times. So there is very little
> overhead of this call even with multiple mode_valid() called during
> display run.
>  From weston-simple-egl application, I have seen that there is no frame
> drop or performance impact.
> 
> Once this patch gets in, I will send patches for AM62P and J722S DSS
> support.
> 
>   drivers/gpu/drm/tidss/tidss_dispc.c | 76 ++++++++++++-----------------
>   drivers/gpu/drm/tidss/tidss_dispc.h |  1 -
>   drivers/gpu/drm/tidss/tidss_drv.h   |  2 +
>   3 files changed, 34 insertions(+), 45 deletions(-)
> 

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