linux-kernel - Re: [PATCH v3 2/3] drm/msm/disp/dpu1: add helper to know if display is builtin

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Message-ID: <8b2999d9-87e4-fe29-6283-15200a052131@linaro.org>
Date:   Fri, 18 Nov 2022 17:00:35 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Kalyan Thota <kalyant@....qualcomm.com>,
        "Kalyan Thota (QUIC)" <quic_kalyant@...cinc.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "freedreno@...ts.freedesktop.org" <freedreno@...ts.freedesktop.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "robdclark@...omium.org" <robdclark@...omium.org>,
        "dianders@...omium.org" <dianders@...omium.org>,
        "swboyd@...omium.org" <swboyd@...omium.org>,
        "Vinod Polimera (QUIC)" <quic_vpolimer@...cinc.com>,
        "Abhinav Kumar (QUIC)" <quic_abhinavk@...cinc.com>
Subject: Re: [PATCH v3 2/3] drm/msm/disp/dpu1: add helper to know if display
 is builtin

On 18/11/2022 16:37, Kalyan Thota wrote:
> 
> 
>> -----Original Message-----
>> From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
>> Sent: Friday, November 18, 2022 6:09 PM
>> To: Kalyan Thota (QUIC) <quic_kalyant@...cinc.com>; dri-
>> devel@...ts.freedesktop.org; linux-arm-msm@...r.kernel.org;
>> freedreno@...ts.freedesktop.org; devicetree@...r.kernel.org
>> Cc: linux-kernel@...r.kernel.org; robdclark@...omium.org;
>> dianders@...omium.org; swboyd@...omium.org; Vinod Polimera (QUIC)
>> <quic_vpolimer@...cinc.com>; Abhinav Kumar (QUIC)
>> <quic_abhinavk@...cinc.com>
>> Subject: Re: [PATCH v3 2/3] drm/msm/disp/dpu1: add helper to know if display is
>> builtin
>>
>> WARNING: This email originated from outside of Qualcomm. Please be wary of
>> any links or attachments, and do not enable macros.
>>
>> On 18/11/2022 15:16, Kalyan Thota wrote:
>>> Since DRM encoder type for few encoders can be similar (like eDP and
>>> DP) find out if the interface supports HPD from encoder bridge to
>>> differentiate between builtin and pluggable displays.
>>>
>>> Changes in v1:
>>> - add connector type in the disp_info (Dmitry)
>>> - add helper functions to know encoder type
>>> - update commit text reflecting the change
>>>
>>> Changes in v2:
>>> - avoid hardcode of connector type for DSI as it may not be true
>>> (Dmitry)
>>> - get the HPD information from encoder bridge
>>>
>>> Changes in v3:
>>> - use bridge type instead of bridge ops in determining connector
>>> (Dmitry)
>>>
>>> Signed-off-by: Kalyan Thota <quic_kalyant@...cinc.com>
>>> ---
>>>    drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 27
>> +++++++++++++++++++++++++++
>>>    drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.h |  6 ++++++
>>>    2 files changed, 33 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
>>> b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
>>> index 9c6817b..574f2b0 100644
>>> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
>>> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
>>> @@ -15,6 +15,7 @@
>>>    #include <drm/drm_crtc.h>
>>>    #include <drm/drm_file.h>
>>>    #include <drm/drm_probe_helper.h>
>>> +#include <drm/drm_bridge.h>
>>>
>>>    #include "msm_drv.h"
>>>    #include "dpu_kms.h"
>>> @@ -217,6 +218,32 @@ static u32 dither_matrix[DITHER_MATRIX_SZ] = {
>>>        15, 7, 13, 5, 3, 11, 1, 9, 12, 4, 14, 6, 0, 8, 2, 10
>>>    };
>>>
>>> +bool dpu_encoder_is_builtin(struct drm_encoder *encoder) {
>>> +     struct drm_bridge *bridge;
>>> +     int ops = 0;
>>> +
>>> +     if (!encoder)
>>> +             return false;
>>> +
>>> +     /* Get last bridge in the chain to determine connector type */
>>> +     drm_for_each_bridge_in_chain(encoder, bridge)
>>> +             if (!drm_bridge_get_next_bridge(bridge))
>>> +                     ops = bridge->type;
>>
>> Why don't we check the connector type directly? You should not assume that
>> connector's type is equal to the latest bridge's type.
> 
> if we need to get the type from connector, need to do something as below.
> Are you thinking on the same lines ?
> 
> "to_drm_bridge_connector" macro needs to be moved to drm_bridge_connector.h
> 
> struct drm_bridge_connector *bridge_connector;
> 
> drm_connector_list_iter_begin(dev, &conn_iter);
> 	drm_for_each_connector_iter(connector, &conn_iter) {
> 
> 		bridge_connector = to_drm_bridge_connector(connector);
> 		if (bridge_connector->encoder == encoder) {
> 			type = connector->connector_type;
> 			break;
> 		}
> 	}
> drm_connector_list_iter_end(&conn_iter);

No. You can not depend on the idea that every connector is 
drm_bridge_connector. Some bridges might create their own connectors. 
However you can do it in the following way:

drm_connector_list_iter_begin(dev, &iter);
drm_for_each_connector_iter(connector, &iter) {
  if (connector->possible_encoders & drm_encoder_mask(encoder)) {
     builtin = (connector->connector_type == DRM_MODE_CONNECTOR_LVDS) || 
...;
     break;
   }
}
drm_connector_list_iter_end(&iter);

return builtin;


> 
> 
>>> +
>>> +     switch (ops) {
>>> +     case DRM_MODE_CONNECTOR_Unknown:
>>> +     case DRM_MODE_CONNECTOR_LVDS:
>>> +     case DRM_MODE_CONNECTOR_eDP:
>>> +     case DRM_MODE_CONNECTOR_DSI:
>>> +     case DRM_MODE_CONNECTOR_DPI:
>>> +     case DRM_MODE_CONNECTOR_WRITEBACK:
>>> +     case DRM_MODE_CONNECTOR_VIRTUAL:
>>
>> Unknown, WRITEBACK and VIRTUAL are not builtin (for the point of CTM at
>> least).
>>
>>> +             return true;
>>> +     default:
>>> +             return false;
>>> +     }
>>> +}
>>>
>>>    bool dpu_encoder_is_widebus_enabled(const struct drm_encoder *drm_enc)
>>>    {
>>> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.h
>>> b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.h
>>> index 9e7236e..7f3d823 100644
>>> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.h
>>> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.h
>>> @@ -224,4 +224,10 @@ void dpu_encoder_cleanup_wb_job(struct
>> drm_encoder *drm_enc,
>>>     */
>>>    bool dpu_encoder_is_valid_for_commit(struct drm_encoder *drm_enc);
>>>
>>> +/**
>>> + * dpu_encoder_is_builtin - find if the encoder is of type builtin
>>> + * @drm_enc:    Pointer to previously created drm encoder structure
>>> + */
>>> +bool dpu_encoder_is_builtin(struct drm_encoder *drm_enc);
>>> +
>>>    #endif /* __DPU_ENCODER_H__ */
>>
>> --
>> With best wishes
>> Dmitry
> 

-- 
With best wishes
Dmitry