Re: [PATCH v4 0/9] MediaTek DisplayPort: support eDP and aux-bus

[AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>]

Il 07/07/23 10:23, Chen-Yu Tsai ha scritto:
> On Thu, Jul 6, 2023 at 8:30 PM AngeloGioacchino Del Regno
> <angelogioacchino.delregno@collabora.com> wrote:
>>
>> Changes in v4:
>>   - Set data lanes to idle to prevent stalls if bootloader didn't
>>     properly close the eDP port
>>   - Now using the .done_probing() callback for AUX bus to prevent
>>     probe deferral loops in case the panel-edp driver is a module
>>     as previously seen with another bridge driver (ANX7625) on
>>     some other SoCs (MT8192 and others)
>>   - Rebased over next-20230706
>>   - Dropped Chen-Yu's T-b tag on last patch as some logic changed
>>     (before, I wasn't using the .done_probing() callback).
>>
>> 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)
> 
> Do you have panel-edp built as a module? If I have it built in, the panel
> can correctly display stuff. If I have it built as a module, the panel is
> correctly detected, but the panel stays black even if DRM thinks it is
> displaying stuff.
> 

I tested both. I'll recheck on a clean tree just to be sure...

> And it looks like EDID reading and panel power sequencing is still not
> working correctly, i.e. needs regulator-always-on?

Yeah that's still needed with this version, I'm still trying to get *at least*
some support upstreamed before refining it.

Cheers,
Angelo

> 
> ChenYu
> 
>> 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
>>
>>   drivers/gpu/drm/mediatek/mtk_dp.c | 197 +++++++++++++++++++-----------
>>   1 file changed, 127 insertions(+), 70 deletions(-)
>>
>> --
>> 2.40.1
>>