linux-kernel - Re: [v3 4/6] drm/vs: Add KMS crtc&plane

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Date:   Thu, 07 Dec 2023 16:41:56 +0800
From:   Icenowy Zheng <uwu@...nowy.me>
To:     Keith Zhao <keith.zhao@...rfivetech.com>,
        devicetree@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Cc:     aou@...s.berkeley.edu, suijingfeng@...ngson.cn,
        tzimmermann@...e.de, paul.walmsley@...ive.com, mripard@...nel.org,
        xingyu.wu@...rfivetech.com, jack.zhu@...rfivetech.com,
        palmer@...belt.com, krzysztof.kozlowski+dt@...aro.org,
        william.qiu@...rfivetech.com, shengyang.chen@...rfivetech.com,
        changhuang.liang@...rfivetech.com
Subject: Re: [v3 4/6] drm/vs: Add KMS crtc&plane

在 2023-12-04星期一的 20:33 +0800，Keith Zhao写道：
*snip*

> +static void update_cursor_plane(struct vs_dc *dc, struct vs_plane
> *plane,
> +                               struct drm_plane *drm_plane,
> +                               struct drm_atomic_state *drm_state)
> +{
> +       struct drm_plane_state *state =
> drm_atomic_get_new_plane_state(drm_state,
> +                                                                    
>   drm_plane);
> +       struct vs_plane_state *plane_state =
> to_vs_plane_state(state);
> +       struct drm_framebuffer *drm_fb = state->fb;
> +       struct dc_hw_cursor cursor;
> +
> +       cursor.address = plane_state->dma_addr[0];
> +       cursor.x = state->crtc_x;
> +       cursor.y = state->crtc_y;

From my experiments on poking with registers on T-Head TH1520 (also
uses DC8200 display controller and a similar driver), the DC8200
hardware have a different definition of cursor position X and Y with
the CRTC plane state.

For CRTC plane state, hot_x and hot_y are only provided as reference,
and the cursor should be displayed with its (0,0) drawn to (crtc_x,
crtc_y) ([XY]_crtc are values specified in CRTC state, the right part
of the assignments here), when the cursor is moved to (0,0) but the hot
point is not (0,0), it could be negative.

However, for DC8200 registers definition, cursor XY position could not
be negative -- the cursor will disappear then; because in its
definition, the cursor XY position should be where the cursor is
pointing to, instead of its (0,0). DC8200 will draw (0,0) of the cursor
to (x - hot_x, y - hot_y). So to met the expectation of the KMS plane
settings, the DC8200 position should be set to (crtc_x + hot_x, crtc_y
+ hot_y) instead. Thus these two lines of code should be:

```
        cursor.x = state->crtc_x + drm_fb->hot_x;
        cursor.y = state->crtc_y + drm_fb->hot_y;
```


> +       cursor.hot_x = drm_fb->hot_x;
> +       cursor.hot_y = drm_fb->hot_y;
> +       cursor.display_id = to_vs_display_id(dc, state->crtc);
> +       update_cursor_size(state, &cursor);
> +       cursor.enable = true;
> +
> +       dc_hw_update_cursor(&dc->hw, cursor.display_id, &cursor);
> +}
*snip