linux-kernel - Re: [PATCH v4 3/3] drm/tidss: oldi: Add atomic

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Message-ID: <426fd0c1-1de5-4b39-9e7b-9532e522d5a3@ideasonboard.com>
Date: Thu, 17 Jul 2025 19:10:42 +0300
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Jayesh Choudhary <j-choudhary@...com>
Cc: airlied@...il.com, simona@...ll.ch, linux-kernel@...r.kernel.org,
 jyri.sarha@....fi, maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
 tzimmermann@...e.de, dri-devel@...ts.freedesktop.org, devarsht@...com,
 mwalle@...nel.org
Subject: Re: [PATCH v4 3/3] drm/tidss: oldi: Add atomic_check hook for oldi
 bridge

Hi,

On 04/07/2025 12:48, Jayesh Choudhary wrote:
> Since OLDI consumes DSS VP clock directly as serial clock, certain

I don't think that's true. Although depends what you mean with VP clock.
I think VP clock is whatever pclk goes into the DSS.

OLDI gets a serial clock from the PLL. That same clock also goes through
a divider, and then goes into DSS as the VP clock.

And the problem is, if I'm not mistaken, that the DSS can't
clk_set_rate()/clk_round_rate() to the VP clock, as the divider won't
propagate the rate change to the PLL. Another problem is that the OLDI
driver is controlling the clock, so DSS shouldn't.

As a side topic/question, I wonder if the divider should propagate the
rate change, and DSS should be in control of the clock...

> checks cannot be performed in tidss driver which should be checked

"certain checks"? It's not good to be very vague in the patch descriptions.

> in oldi driver. Add check for mode clock and set the curr_max_pclk
> field for tidss in case the VP is OLDI.

The check part makes sense after reading the description, but the
"curr_max_pclk" part doesn't. I think it needs a few extra words. But
also, the code is the same as in DSS, isn't it... Maybe OLDI can just
call check_pixel_clock() (or whatever it is named, perhaps with the
changes I mentioned in the previous mail).

 Tomi

> Fixes: 7246e0929945 ("drm/tidss: Add OLDI bridge support")
> Reviewed-by: Devarsh Thakkar <devarsht@...com>
> Signed-off-by: Jayesh Choudhary <j-choudhary@...com>
> ---
>  drivers/gpu/drm/tidss/tidss_oldi.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/drivers/gpu/drm/tidss/tidss_oldi.c b/drivers/gpu/drm/tidss/tidss_oldi.c
> index 63e07c8edeaa..486e7373531b 100644
> --- a/drivers/gpu/drm/tidss/tidss_oldi.c
> +++ b/drivers/gpu/drm/tidss/tidss_oldi.c
> @@ -309,6 +309,29 @@ static u32 *tidss_oldi_atomic_get_input_bus_fmts(struct drm_bridge *bridge,
>  	return input_fmts;
>  }
>  
> +static int tidss_oldi_atomic_check(struct drm_bridge *bridge,
> +				   struct drm_bridge_state *bridge_state,
> +				   struct drm_crtc_state *crtc_state,
> +				   struct drm_connector_state *conn_state)
> +{
> +	struct tidss_oldi *oldi = drm_bridge_to_tidss_oldi(bridge);
> +	struct drm_display_mode *adjusted_mode;
> +	unsigned long round_clock;
> +
> +	adjusted_mode = &crtc_state->adjusted_mode;
> +
> +	if (adjusted_mode->clock > oldi->tidss->curr_max_pclk[oldi->parent_vp]) {
> +		round_clock = clk_round_rate(oldi->serial, adjusted_mode->clock * 7 * 1000);
> +
> +		if (dispc_pclk_diff(adjusted_mode->clock * 7 * 1000, round_clock) > 5)
> +			return -EINVAL;
> +
> +		oldi->tidss->curr_max_pclk[oldi->parent_vp] = round_clock;
> +	}
> +
> +	return 0;
> +}
> +
>  static const struct drm_bridge_funcs tidss_oldi_bridge_funcs = {
>  	.attach	= tidss_oldi_bridge_attach,
>  	.atomic_pre_enable = tidss_oldi_atomic_pre_enable,
> @@ -317,6 +340,7 @@ static const struct drm_bridge_funcs tidss_oldi_bridge_funcs = {
>  	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
>  	.atomic_destroy_state = drm_atomic_helper_bridge_destroy_state,
>  	.atomic_reset = drm_atomic_helper_bridge_reset,
> +	.atomic_check = tidss_oldi_atomic_check,
>  };
>  
>  static int get_oldi_mode(struct device_node *oldi_tx, int *companion_instance)