linux-kernel - Re: [PATCH 4/4] drm/tidss: Fix sampling edge configuration

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Message-ID: <20250804-tuscan-woodpecker-from-jupiter-9d290f@kuoka>
Date: Mon, 4 Aug 2025 10:06:37 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Louis Chauvet <louis.chauvet@...tlin.com>
Cc: Jyri Sarha <jyri.sarha@....fi>, 
	Tomi Valkeinen <tomi.valkeinen@...asonboard.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
	Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Sam Ravnborg <sam@...nborg.org>, Benoit Parrot <bparrot@...com>, Lee Jones <lee@...nel.org>, 
	Nishanth Menon <nm@...com>, Vignesh Raghavendra <vigneshr@...com>, 
	Tero Kristo <kristo@...nel.org>, thomas.petazzoni@...tlin.com, Jyri Sarha <jsarha@...com>, 
	Tomi Valkeinen <tomi.valkeinen@...com>, dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, stable@...r.kernel.org
Subject: Re: [PATCH 4/4] drm/tidss: Fix sampling edge configuration

On Wed, Jul 30, 2025 at 07:02:47PM +0200, Louis Chauvet wrote:
> As stated in the AM62x Technical Reference Manual (SPRUIV7B), the data
> sampling edge needs to be configured in two distinct registers: one in the
> TIDSS IP and another in the memory-mapped control register modules. Since
> the latter is not within the same address range, a phandle to a syscon
> device is used to access the regmap.
> 
> Fixes: 32a1795f57ee ("drm/tidss: New driver for TI Keystone platform Display SubSystem")
> Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
> 
> ---
> 
> Cc: stable@...r.kernel.org

Please read docs how to add stable tags.

> ---
>  drivers/gpu/drm/tidss/tidss_dispc.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/drivers/gpu/drm/tidss/tidss_dispc.c b/drivers/gpu/drm/tidss/tidss_dispc.c
> index c0277fa36425ee1f966dccecf2b69a2d01794899..65ca7629a2e75437023bf58f8a1bddc24db5e3da 100644
> --- a/drivers/gpu/drm/tidss/tidss_dispc.c
> +++ b/drivers/gpu/drm/tidss/tidss_dispc.c
> @@ -498,6 +498,7 @@ struct dispc_device {
>  	const struct dispc_features *feat;
>  
>  	struct clk *fclk;
> +	struct regmap *clk_ctrl;
>  
>  	bool is_enabled;
>  
> @@ -1267,6 +1268,11 @@ void dispc_vp_enable(struct dispc_device *dispc, u32 hw_videoport,
>  		       FLD_VAL(mode->vdisplay - 1, 27, 16));
>  
>  	VP_REG_FLD_MOD(dispc, hw_videoport, DISPC_VP_CONTROL, 1, 0, 0);
> +
> +	if (dispc->clk_ctrl) {
> +		regmap_update_bits(dispc->clk_ctrl, 0, 0x100, ipc ? 0x100 : 0x000);
> +		regmap_update_bits(dispc->clk_ctrl, 0, 0x200, rf ? 0x200 : 0x000);
> +	}
>  }
>  
>  void dispc_vp_disable(struct dispc_device *dispc, u32 hw_videoport)
> @@ -3012,6 +3018,14 @@ int dispc_init(struct tidss_device *tidss)
>  
>  	dispc_init_errata(dispc);
>  
> +	dispc->clk_ctrl = syscon_regmap_lookup_by_phandle_optional(tidss->dev->of_node,
> +								   "ti,clk-ctrl");
> +	if (IS_ERR(dispc->clk_ctrl)) {
> +		r = dev_err_probe(dispc->dev, PTR_ERR(dispc->clk_ctrl),
> +				  "DISPC: syscon_regmap_lookup_by_phandle failed.\n");
> +		return r;

This breaks ABI. Commit msg mentions the reason but without
justification - was everything broken? Nothing was working? Was it ever
tested?

And anyway ABI impact must be clearly documented.


Best regards,
Krzysztof