Re: [PATCH 13/14] drm/bridge: synopsys: Add DW HDMI QP TX controller driver

[Cristian Ciocaltea]

On 6/5/24 2:48 PM, Neil Armstrong wrote:
> On 05/06/2024 12:11, Cristian Ciocaltea wrote:
>> On 6/5/24 12:34 AM, Cristian Ciocaltea wrote:
>>> On 6/4/24 11:41 PM, Sam Ravnborg wrote:
>>>> Hi Cristian.
>>>>
>>>> On Tue, Jun 04, 2024 at 10:32:04PM +0300, Cristian Ciocaltea wrote:
>>>>> Hi Sam,
>>>>>
>>>>> On 6/1/24 5:32 PM, Sam Ravnborg wrote:
>>>>>> Hi Cristian,
>>>>>>
>>>>>> a few drive-by comments below.
>>>>>>
>>>>>>     Sam
>>>>>>
>>>>>>
>>>>>>> +
>>>>>>> +static const struct drm_connector_funcs
>>>>>>> dw_hdmi_qp_connector_funcs = {
>>>>>>> +    .fill_modes = drm_helper_probe_single_connector_modes,
>>>>>>> +    .detect = dw_hdmi_connector_detect,
>>>>>>> +    .destroy = drm_connector_cleanup,
>>>>>>> +    .force = dw_hdmi_qp_connector_force,
>>>>>>> +    .reset = drm_atomic_helper_connector_reset,
>>>>>>> +    .atomic_duplicate_state =
>>>>>>> drm_atomic_helper_connector_duplicate_state,
>>>>>>> +    .atomic_destroy_state =
>>>>>>> drm_atomic_helper_connector_destroy_state,
>>>>>>> +};
>>>>>>> +
>>>>>>> +static int dw_hdmi_qp_bridge_attach(struct drm_bridge *bridge,
>>>>>>> +                    enum drm_bridge_attach_flags flags)
>>>>>>> +{
>>>>>>> +    struct dw_hdmi *hdmi = bridge->driver_private;
>>>>>>> +
>>>>>>> +    if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)
>>>>>>> +        return drm_bridge_attach(bridge->encoder,
>>>>>>> hdmi->next_bridge,
>>>>>>> +                     bridge, flags);
>>>>>>> +
>>>>>>> +    return dw_hdmi_connector_create(hdmi,
>>>>>>> &dw_hdmi_qp_connector_funcs);
>>>>>>> +}
>>>>>>
>>>>>> Are there any users left that requires the display driver to
>>>>>> create the
>>>>>> connector?
>>>>>> In other words - could this driver fail if
>>>>>> DRM_BRIDGE_ATTACH_NO_CONNECTOR
>>>>>> is not passed and drop dw_hdmi_connector_create()?
>>>>>>
>>>>>> I did not try to verify this - just a naive question.
>>>>>
>>>>> I've just tested this and it doesn't work - dw_hdmi_connector_create()
>>>>> is still needed.
>>>>
>>>> Hmm, seems the display driver or some other bridge driver fails to
>>>> support "DRM_BRIDGE_ATTACH_NO_CONNECTOR".
>>>> what other drivers are involved?
>>>
>>> Could it be related to the glue driver (updated in the next patch) which
>>> is also responsible for setting up the encoder?
>>>
>>>> Note that my comments here should be seen as potential future
>>>> improvements, and do not block the patch from being used.
>>>
>>> Thanks for the heads up! Will try to get back to this soon and
>>> investigate.
>>   IIUC, modern bridges should not create the connector but rely on
>> display
>> drivers to take care of, which in this case is the VOP2 driver. However,
>> it also handles some of the older SoCs relying on the non-QP variant of
>> DW HDMI IP. Hence the existing dw-hdmi driver would be also impacted in
>> order to come up with a proper solution.
>>
>> A quick check shows there are several users of this IP:
>>
>> $ git grep -E '= dw_hdmi_(bind|probe)\('
>> drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx.c:    hdmi->dw_hdmi =
>> dw_hdmi_probe(pdev, plat_data);
>> drivers/gpu/drm/bridge/synopsys/dw-hdmi.c:      hdmi =
>> dw_hdmi_probe(pdev, plat_data);
>> drivers/gpu/drm/imx/ipuv3/dw_hdmi-imx.c:        hdmi->hdmi =
>> dw_hdmi_probe(pdev, match->data);
>> drivers/gpu/drm/ingenic/ingenic-dw-hdmi.c:      hdmi =
>> dw_hdmi_probe(pdev, &ingenic_dw_hdmi_plat_data);
>> drivers/gpu/drm/meson/meson_dw_hdmi.c:  meson_dw_hdmi->hdmi =
>> dw_hdmi_probe(pdev, &meson_dw_hdmi->dw_plat_data);
>> drivers/gpu/drm/renesas/rcar-du/rcar_dw_hdmi.c: hdmi =
>> dw_hdmi_probe(pdev, &rcar_dw_hdmi_plat_data);
>> drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c:            hdmi->hdmi =
>> dw_hdmi_bind(pdev, encoder, plat_data);
>> drivers/gpu/drm/sun4i/sun8i_dw_hdmi.c:  hdmi->hdmi =
>> dw_hdmi_bind(pdev, encoder, plat_data);
>>
>> I didn't check which display drivers would be involved, I'd guess there
>> are quite a few of them as well. So it seems this ends up being a pretty
>> complex task.
> 
> If this would be a brand new driver, then it should only support
> DRM_BRIDGE_ATTACH_NO_CONNECTOR,
> so you should not create a connector from the driver.
> 
> The fact dw-hdmi accepts an attach without the flag is for legacy purpose
> since some DRM drivers haven't switched to
> DRM_BRIDGE_ATTACH_NO_CONNECTOR yes,
> but it's a requirement for new bridges so at some point you'll need to make
> sure the rockchip glue and drm driver supports
> DRM_BRIDGE_ATTACH_NO_CONNECTOR.
> 
> This will greatly simplify the driver!

Got it, thanks for the clarifications!

Cristian