Message-ID: <CAGXv+5FEEkMg+SY7ZkSHN2G9jtT6TBiN9MadZmYGMX_uVi5=gQ@mail.gmail.com>
Date:   Thu, 6 Apr 2023 15:20:37 +0800
From:   Chen-Yu Tsai <wenst@...omium.org>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
Cc:     chunkuang.hu@...nel.org, p.zabel@...gutronix.de, airlied@...il.com,
        daniel@...ll.ch, matthias.bgg@...il.com,
        dri-devel@...ts.freedesktop.org,
        linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kernel@...labora.com
Subject: Re: [PATCH v3 0/9] MediaTek DisplayPort: support eDP and aux-bus

On Tue, Apr 4, 2023 at 6:48 PM AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com> wrote:
>
> Changes in v3:
>  - Added DPTX AUX block initialization before trying to communicate
>    to stop relying on the bootloader keeping it initialized before
>    booting Linux.
>  - Fixed commit description for patch [09/09] and removed commented
>    out code (that slipped from dev phase.. sorry!).
>
> This series adds "real" support for eDP in the mtk-dp DisplayPort driver.
>
> Explaining the "real":
> Before this change, the DisplayPort driver did support eDP to some
> extent, but it was treating it entirely like a regular DP interface
> which is partially fine, after all, embedded DisplayPort *is* actually
> DisplayPort, but there might be some differences to account for... and
> this is for both small performance improvements and, more importantly,
> for correct functionality in some systems.
>
> Functionality first:
>
> One of the common differences found in various boards implementing eDP
> and machines using an eDP panel is that many times the HPD line is not
> connected. This *must* be accounted for: at startup, this specific IP
> will raise a HPD interrupt (which should maybe be ignored... as it does
> not appear to be a "real" event...) that will make the eDP panel to be
> detected and to actually work but, after a suspend-resume cycle, there
> will be no HPD interrupt (as there's no HPD line in my case!) producing
> a functionality issue - specifically, the DP Link Training fails because
> the panel doesn't get powered up, then it stays black and won't work
> until rebooting the machine (or removing and reinserting the module I
> think, but I haven't tried that).
>
> Now for.. both:
> eDP panels are *e*DP because they are *not* removable (in the sense that
> you can't unplug the cable without disassembling the machine, in which
> case, the machine shall be powered down..!): this (correct) assumption
> makes us able to solve some issues and to also gain a little performance
> during PM operations.
>
> What was done here is:
>  - Caching the EDID if the panel is eDP: we're always going to read the
>    same data everytime, so we can just cache that (as it's small enough)
>    shortening PM resume times for the eDP driver instance;
>  - Always return connector_status_connected if it's eDP: non-removable
>    means connector_status_disconnected can't happen during runtime...
>    this also saves us some time and even power, as we won't have to
>    perform yet another power cycle of the HW;
>  - Added aux-bus support!
>    This makes us able to rely on panel autodetection from the EDID,
>    avoiding to add more and more panel timings to panel-edp and, even
>    better, allowing to use one panel node in devicetrees for multiple
>    variants of the same machine since, at that point, it's not important
>    to "preventively know" what panel we have (eh, it's autodetected...!).
>
> This was tested on a MT8195 Cherry Tomato Chromebook (panel-edp on aux-bus)
>
>
> P.S.: For your own testing commodity, here's a reference devicetree:
> &edp_tx {
>         status = "okay";
>
>         pinctrl-names = "default";
>         pinctrl-0 = <&edptx_pins_default>;
>
>         ports {
>                 #address-cells = <1>;
>                 #size-cells = <0>;
>
>                 port@0 {
>                         reg = <0>;
>                         edp_in: endpoint {
>                                 remote-endpoint = <&dp_intf0_out>;
>                         };
>                 };
>
>                 port@1 {
>                         reg = <1>;
>                         edp_out: endpoint {
>                                 data-lanes = <0 1 2 3>;
>                                 remote-endpoint = <&panel_in>;
>                         };
>                 };
>         };
>
>         aux-bus {
>                 panel: panel {
>                         compatible = "edp-panel";
>                         power-supply = <&pp3300_disp_x>;
>                         backlight = <&backlight_lcd0>;
>                         port {
>                                 panel_in: endpoint {
>                                         remote-endpoint = <&edp_out>;
>                                 };
>                         };
>                 };
>         };
> };
>
> AngeloGioacchino Del Regno (9):
>   drm/mediatek: dp: Cache EDID for eDP panel
>   drm/mediatek: dp: Move AUX and panel poweron/off sequence to function
>   drm/mediatek: dp: Always return connected status for eDP in .detect()
>   drm/mediatek: dp: Always set cable_plugged_in at resume for eDP panel
>   drm/mediatek: dp: Change logging to dev for mtk_dp_aux_transfer()
>   drm/mediatek: dp: Enable event interrupt only when bridge attached
>   drm/mediatek: dp: Use devm variant of drm_bridge_add()
>   drm/mediatek: dp: Move AUX_P0 setting to
>     mtk_dp_initialize_aux_settings()
>   drm/mediatek: dp: Add support for embedded DisplayPort aux-bus

Tested-by: Chen-Yu Tsai <wenst@...omium.org>

on MT8195 Tomato: eDP panel works if the display panel regulator is always
on. External DP works.

Maybe it has something to do with the driver not supporting .wait_hpd_asserted
and not using a GPIO for HPD?

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