linux-kernel - Re: [PATCH v5 3/3] drm/tidss: oldi: Add atomic

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <837a8381-02bd-4882-bfa4-6d5c34f44119@ideasonboard.com>
Date: Wed, 27 Aug 2025 12:05:04 +0300
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Swamil Jain <s-jain1@...com>
Cc: h-shenoy@...com, devarsht@...com, vigneshr@...com, praneeth@...com,
 u-kumar1@...com, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, jyri.sarha@....fi,
 maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de,
 airlied@...il.com, simona@...ll.ch, aradhya.bhatia@...ux.dev
Subject: Re: [PATCH v5 3/3] drm/tidss: oldi: Add atomic_check hook for oldi
 bridge

Hi,

On 19/08/2025 22:21, Swamil Jain wrote:
> From: Jayesh Choudhary <j-choudhary@...com>
> 
> Since OLDI consumes DSS VP clock directly as serial clock, certain
> checks cannot be performed in tidss driver which should be checked

I think this is a bit misleading. The OLDI input clock doesn't come from
DSS, so I wouldn't call it "DSS VP clock". The point here is that the
clock from the PLL is used by both OLDI and DSS, and in the current
architecture the OLDI driver manages the clock, so the DSS driver can't
really do checks, it just has to accept the clock rate. All checks need
to be done in the OLDI driver.

> in OLDI driver. Add check for mode clock and set max_successful_rate
> and max_attempted_rate field for tidss in case the VP is OLDI.
> 
> Fixes: 7246e0929945 ("drm/tidss: Add OLDI bridge support")
> Reviewed-by: Devarsh Thakkar <devarsht@...com>
> Signed-off-by: Jayesh Choudhary <j-choudhary@...com>
> Signed-off-by: Swamil Jain <s-jain1@...com>
> ---
>  drivers/gpu/drm/tidss/tidss_oldi.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/drivers/gpu/drm/tidss/tidss_oldi.c b/drivers/gpu/drm/tidss/tidss_oldi.c
> index ef01ecc17a12..2ed2d0666ccb 100644
> --- a/drivers/gpu/drm/tidss/tidss_oldi.c
> +++ b/drivers/gpu/drm/tidss/tidss_oldi.c
> @@ -309,6 +309,30 @@ 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->max_successful_rate[oldi->parent_vp]) {

You can change the above check to <=, and return 0 here early.

> +		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->max_successful_rate[oldi->parent_vp] = round_clock;
> +		oldi->tidss->max_attempted_rate[oldi->parent_vp] = adjusted_mode->clock * 7 * 1000;
> +	}

This is not very nice. We should have a function in tidss that we call
here, instead of poking into these tidss's variables directly.

Actually... Do we even need to use the tidss->max_* fields? The above
code is not checking the VP clock maximum, it's actually looking at the
serial clock maximum. Currently those two clocks are linked, though, but
would it make more sense to have the max_* fields here, in OLDI, for
OLDI's serial clock?

 Tomi

> +
> +	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 +341,7 @@ 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)