linux-kernel - Re: [RFC PATCH v5 3/6] drm/tidss: Add support for AM625 DSS

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Message-ID: <eae03891-c814-87fd-d1a6-099b855ca7fb@ideasonboard.com>
Date:   Wed, 12 Oct 2022 15:09:17 +0300
From:   Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To:     Aradhya Bhatia <a-bhatia1@...com>, Jyri Sarha <jyri.sarha@....fi>,
        Rob Herring <robh+dt@...nel.org>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc:     Nishanth Menon <nm@...com>, Vignesh Raghavendra <vigneshr@...com>,
        Rahul T R <r-ravikumar@...com>,
        DRI Development List <dri-devel@...ts.freedesktop.org>,
        Devicetree List <devicetree@...r.kernel.org>,
        Linux Kernel List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v5 3/6] drm/tidss: Add support for AM625 DSS

On 28/09/2022 20:52, Aradhya Bhatia wrote:
> Add support for the DSS controller on TI's new AM625 SoC in the tidss
> driver.
> 
> The first video port (VP0) in am625-dss can output OLDI signals through
> 2 OLDI TXes. A 3rd port has been added with "DISPC_VP_OLDI" bus type.
> 
> Signed-off-by: Aradhya Bhatia <a-bhatia1@...com>
> ---
>   drivers/gpu/drm/tidss/tidss_dispc.c | 61 ++++++++++++++++++++++++++++-
>   drivers/gpu/drm/tidss/tidss_dispc.h |  3 ++
>   drivers/gpu/drm/tidss/tidss_drv.c   |  1 +
>   3 files changed, 64 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/tidss/tidss_dispc.c b/drivers/gpu/drm/tidss/tidss_dispc.c
> index dd3c6a606ae2..34f0da4bb3e3 100644
> --- a/drivers/gpu/drm/tidss/tidss_dispc.c
> +++ b/drivers/gpu/drm/tidss/tidss_dispc.c
> @@ -93,6 +93,7 @@ const struct dispc_features dispc_k2g_feats = {
>   	.common_regs = tidss_k2g_common_regs,
>   
>   	.num_vps = 1,
> +	.num_max_ports = 1,
>   	.vp_name = { "vp1" },
>   	.ovr_name = { "ovr1" },
>   	.vpclk_name =  { "vp1" },
> @@ -168,6 +169,7 @@ const struct dispc_features dispc_am65x_feats = {
>   	.common_regs = tidss_am65x_common_regs,
>   
>   	.num_vps = 2,
> +	.num_max_ports = 2,
>   	.vp_name = { "vp1", "vp2" },
>   	.ovr_name = { "ovr1", "ovr2" },
>   	.vpclk_name =  { "vp1", "vp2" },
> @@ -257,6 +259,7 @@ const struct dispc_features dispc_j721e_feats = {
>   	.common_regs = tidss_j721e_common_regs,
>   
>   	.num_vps = 4,
> +	.num_max_ports = 4,
>   	.vp_name = { "vp1", "vp2", "vp3", "vp4" },
>   	.ovr_name = { "ovr1", "ovr2", "ovr3", "ovr4" },
>   	.vpclk_name = { "vp1", "vp2", "vp3", "vp4" },
> @@ -275,6 +278,57 @@ const struct dispc_features dispc_j721e_feats = {
>   	.vid_order = { 1, 3, 0, 2 },
>   };
>   
> +const struct dispc_features dispc_am625_feats = {
> +	.max_pclk_khz = {
> +		[DISPC_VP_DPI] = 165000,
> +		[DISPC_VP_OLDI] = 165000,
> +	},
> +
> +	.scaling = {
> +		.in_width_max_5tap_rgb = 1280,
> +		.in_width_max_3tap_rgb = 2560,
> +		.in_width_max_5tap_yuv = 2560,
> +		.in_width_max_3tap_yuv = 4096,
> +		.upscale_limit = 16,
> +		.downscale_limit_5tap = 4,
> +		.downscale_limit_3tap = 2,
> +		/*
> +		 * The max supported pixel inc value is 255. The value
> +		 * of pixel inc is calculated like this: 1+(xinc-1)*bpp.
> +		 * The maximum bpp of all formats supported by the HW
> +		 * is 8. So the maximum supported xinc value is 32,
> +		 * because 1+(32-1)*8 < 255 < 1+(33-1)*4.
> +		 */
> +		.xinc_max = 32,
> +	},
> +
> +	.subrev = DISPC_AM625,
> +
> +	.common = "common",
> +	.common_regs = tidss_am65x_common_regs,
> +
> +	.num_vps = 2,
> +	/* note: the 3rd port is not representative of a 3rd pipeline */
> +	.num_max_ports = 3,
> +	.vp_name = { "vp1", "vp2" },
> +	.ovr_name = { "ovr1", "ovr2" },
> +	.vpclk_name =  { "vp1", "vp2" },
> +	.vp_bus_type = { DISPC_VP_OLDI, DISPC_VP_DPI, DISPC_VP_OLDI },

Here, for example, we have an issue with the VP vs port. vp_bus_type is 
of size TIDSS_MAX_PORTS (VPs), but you're using it for output ports. If 
we did not have J7, which has 4 VPs, we'd have an overflow bug here.

The meaning of vp_sub_type also becomes a bit unclear. I guess it's 
rather "output_port_bus_type"?

  Tomi