Re: [PATCH 5/7] phy: qcom-qmp-combo: Introduce drm_bridge

[Neil Armstrong <neil.armstrong@linaro.org>]

On 26/04/2023 12:33, Bryan O'Donoghue wrote:
> On Tue, Apr 25, 2023 at 4:40 AM Bjorn Andersson
> <quic_bjorande@quicinc.com> wrote:
>>
>> The QMP combo PHY sits in an of_graph connected between the DisplayPort
>> controller and a USB Type-C connector (or possibly a redriver).
>>
>> The TCPM needs to be able to convey the HPD signal to the DisplayPort
>> controller, but no directly link is provided by DeviceTree so the signal
>> needs to "pass through" the QMP combo phy.
>>
>> Handle this by introducing a drm_bridge which upon initialization finds
>> the next bridge (i.e. the usb-c-connector) and chain this together. This
>> way HPD changes in the connector will propagate to the DisplayPort
>> driver.
>>
>> The connector bridge is resolved lazily, as the TCPM is expected to be
>> able to resolve the typec mux and switch at probe time, so the QMP combo
>> phy will probe before the TCPM.
>>
>> Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>
>> ---
>>   drivers/phy/qualcomm/phy-qcom-qmp-combo.c | 36 +++++++++++++++++++++++
>>   1 file changed, 36 insertions(+)
>>
>> diff --git a/drivers/phy/qualcomm/phy-qcom-qmp-combo.c b/drivers/phy/qualcomm/phy-qcom-qmp-combo.c
>> index 5d6d6ef3944b..84bc08002537 100644
>> --- a/drivers/phy/qualcomm/phy-qcom-qmp-combo.c
>> +++ b/drivers/phy/qualcomm/phy-qcom-qmp-combo.c
>> @@ -22,6 +22,8 @@
>>   #include <linux/usb/typec.h>
>>   #include <linux/usb/typec_mux.h>
>>
>> +#include <drm/drm_bridge.h>
>> +
>>   #include <dt-bindings/phy/phy-qcom-qmp.h>
>>
>>   #include "phy-qcom-qmp.h"
>> @@ -1332,6 +1334,8 @@ struct qmp_combo {
>>          struct clk_hw dp_link_hw;
>>          struct clk_hw dp_pixel_hw;
>>
>> +       struct drm_bridge bridge;
>> +
>>          struct typec_switch_dev *sw;
>>          enum typec_orientation orientation;
>>   };
>> @@ -3196,6 +3200,34 @@ static int qmp_combo_register_clocks(struct qmp_combo *qmp, struct device_node *
>>          return devm_add_action_or_reset(qmp->dev, phy_clk_release_provider, dp_np);
>>   }
>>
>> +static int qmp_combo_bridge_attach(struct drm_bridge *bridge,
>> +                                  enum drm_bridge_attach_flags flags)
>> +{
>> +       struct qmp_combo *qmp = container_of(bridge, struct qmp_combo, bridge);
>> +       struct drm_bridge *next_bridge;
>> +
>> +       if (!(flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR))
>> +               return -EINVAL;
>> +
>> +       next_bridge = devm_drm_of_get_bridge(qmp->dev, qmp->dev->of_node, 0, 0);
>> +       if (IS_ERR(next_bridge))
>> +               return dev_err_probe(qmp->dev, PTR_ERR(next_bridge), "failed to acquire drm_bridge\n");
>> +
>> +       return drm_bridge_attach(bridge->encoder, next_bridge, bridge, DRM_BRIDGE_ATTACH_NO_CONNECTOR);
>> +}
>> +
>> +static const struct drm_bridge_funcs qmp_combo_bridge_funcs = {
>> +       .attach = qmp_combo_bridge_attach,
>> +};
>> +
>> +static int qmp_combo_dp_register_bridge(struct qmp_combo *qmp)
>> +{
>> +       qmp->bridge.funcs = &qmp_combo_bridge_funcs;
>> +       qmp->bridge.of_node = qmp->dev->of_node;
>> +
>> +       return devm_drm_bridge_add(qmp->dev, &qmp->bridge);
>> +}
>> +
>>   static int qmp_combo_parse_dt_lecacy_dp(struct qmp_combo *qmp, struct device_node *np)
>>   {
>>          struct device *dev = qmp->dev;
>> @@ -3459,6 +3491,10 @@ static int qmp_combo_probe(struct platform_device *pdev)
>>          if (ret)
>>                  return ret;
>>
>> +       ret = qmp_combo_dp_register_bridge(qmp);
>> +       if (ret)
>> +               return ret;

I think the DRM part should be only built if CONFIG_DRM is enabled, I don't
have a strong opinion on this, I think Vinod could help here.

>> +
>>          /* Check for legacy binding with child nodes. */
>>          usb_np = of_get_child_by_name(dev->of_node, "usb3-phy");
>>          if (usb_np) {
>> --
>> 2.39.2
>>
> 
> You need to add some or all of these
>         select DRM_DISPLAY_DP_HELPER
>         select DRM_DISPLAY_HELPER
>         select DRM_DP_AUX_BUS
>         select DRM_KMS_HELPER
>         select DRM_MIPI_DSI
>         select DRM_PANEL
> 
> 
> /opt/linaro/gcc-linaro-7.5.0-2019.12-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-ld:
> Unexpected GOT/PLT entries detected!
> /opt/linaro/gcc-linaro-7.5.0-2019.12-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-ld:
> Unexpected run-time procedure linkages detected!
> drivers/phy/qualcomm/phy-qcom-qmp-combo.o: In function
> `qmp_combo_bridge_attach':
> phy-qcom-qmp-combo.c:(.text+0xb50): undefined reference to
> `devm_drm_of_get_bridge'
> phy-qcom-qmp-combo.c:(.text+0xb6c): undefined reference to `drm_bridge_attach'
> drivers/phy/qualcomm/phy-qcom-qmp-combo.o: In function `qmp_combo_probe':
> phy-qcom-qmp-combo.c:(.text+0x13fc): undefined reference to
> `devm_drm_bridge_add'

I think CONFIG_DRM_PANEL_BRIDGE in addition to CONFIG_DRM. should be enough.

With this config added and my drm-bridge hat:

Acked-by: Neil Armstrong <neil.armstrong@linaro.org>

Neil


> 
> ---
> bod