Re: [PATCH v2 01/13] drm/msm/dsi: switch to devm_drm_bridge_add()

[Abhinav Kumar <quic_abhinavk@quicinc.com>]

On 10/9/2023 12:01 PM, Dmitry Baryshkov wrote:
> On 09/10/2023 21:51, Abhinav Kumar wrote:
>>
>>
>> On 10/9/2023 11:46 AM, Dmitry Baryshkov wrote:
>>> On 09/10/2023 21:39, Abhinav Kumar wrote:
>>>>
>>>>
>>>> On 10/9/2023 11:10 AM, Dmitry Baryshkov wrote:
>>>>> Make MSM DSI driver use devm_drm_bridge_add() instead of plain
>>>>> drm_bridge_add(). As the driver doesn't require any additional 
>>>>> cleanup,
>>>>> stop adding created bridge to the priv->bridges array.
>>>>>
>>>>> Reviewed-by: Rob Clark <robdclark@gmail.com>
>>>>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
>>>>> ---
>>>>>   drivers/gpu/drm/msm/dsi/dsi.c         | 28 +++++--------------------
>>>>>   drivers/gpu/drm/msm/dsi/dsi.h         |  3 +--
>>>>>   drivers/gpu/drm/msm/dsi/dsi_manager.c | 30 
>>>>> +++++++++------------------
>>>>>   3 files changed, 16 insertions(+), 45 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/msm/dsi/dsi.c 
>>>>> b/drivers/gpu/drm/msm/dsi/dsi.c
>>>>> index d45e43024802..47f327e68471 100644
>>>>> --- a/drivers/gpu/drm/msm/dsi/dsi.c
>>>>> +++ b/drivers/gpu/drm/msm/dsi/dsi.c
>>>>> @@ -215,20 +215,14 @@ void __exit msm_dsi_unregister(void)
>>>>>   int msm_dsi_modeset_init(struct msm_dsi *msm_dsi, struct 
>>>>> drm_device *dev,
>>>>>                struct drm_encoder *encoder)
>>>>>   {
>>>>> -    struct msm_drm_private *priv = dev->dev_private;
>>>>>       int ret;
>>>>> -    if (priv->num_bridges == ARRAY_SIZE(priv->bridges)) {
>>>>> -        DRM_DEV_ERROR(dev->dev, "too many bridges\n");
>>>>> -        return -ENOSPC;
>>>>> -    }
>>>>> -
>>>>>       msm_dsi->dev = dev;
>>>>>       ret = msm_dsi_host_modeset_init(msm_dsi->host, dev);
>>>>>       if (ret) {
>>>>>           DRM_DEV_ERROR(dev->dev, "failed to modeset init host: 
>>>>> %d\n", ret);
>>>>> -        goto fail;
>>>>> +        return ret;
>>>>>       }
>>>>>       if (msm_dsi_is_bonded_dsi(msm_dsi) &&
>>>>> @@ -242,32 +236,20 @@ int msm_dsi_modeset_init(struct msm_dsi 
>>>>> *msm_dsi, struct drm_device *dev,
>>>>>       msm_dsi->encoder = encoder;
>>>>> -    msm_dsi->bridge = msm_dsi_manager_bridge_init(msm_dsi->id);
>>>>> -    if (IS_ERR(msm_dsi->bridge)) {
>>>>> -        ret = PTR_ERR(msm_dsi->bridge);
>>>>> +    ret = msm_dsi_manager_bridge_init(msm_dsi);
>>>>> +    if (ret) {
>>>>>           DRM_DEV_ERROR(dev->dev, "failed to create dsi bridge: 
>>>>> %d\n", ret);
>>>>> -        msm_dsi->bridge = NULL;
>>>>> -        goto fail;
>>>>> +        return ret;
>>>>>       }
>>>>>       ret = msm_dsi_manager_ext_bridge_init(msm_dsi->id);
>>>>>       if (ret) {
>>>>>           DRM_DEV_ERROR(dev->dev,
>>>>>               "failed to create dsi connector: %d\n", ret);
>>>>> -        goto fail;
>>>>> +        return ret;
>>>>>       }
>>>>> -    priv->bridges[priv->num_bridges++]       = msm_dsi->bridge;
>>>>> -
>>>>>       return 0;
>>>>> -fail:
>>>>> -    /* bridge/connector are normally destroyed by drm: */
>>>>> -    if (msm_dsi->bridge) {
>>>>> -        msm_dsi_manager_bridge_destroy(msm_dsi->bridge);
>>>>> -        msm_dsi->bridge = NULL;
>>>>> -    }
>>>>
>>>> We can drop msm_dsi_manager_bridge_destroy() now but dont we need to 
>>>> keep the part to reset msm_dsi->bridge to NULL in the fail tag if 
>>>> msm_dsi_manager_ext_bridge_init() fails?
>>>
>>> What for? This field is not read in the error /unbinding path.
>>> I'll send a followup that drops msm_dsi->bridge completely.
>>>
>>
>> Not used in the error path. The behavior before this patch was, if 
>> msm_dsi_manager_ext_bridge_init failed, it was marking msm_dsi->bridge 
>> as NULL. Thats what I thought you would want to retain till you drop 
>> the msm_dsi->bridge.
> 
> Why would you like to keep the useless behaviour?
> 

Not sure whether to call it useless. So 
msm_dsi_manager_ext_bridge_init() is referencing msm_dsi->bridge.
msm_dsi_manager_ext_bridge_init() is an exported API. If someone tries 
to call it outside of where its called now, this was the only protection 
against the access?

I guess, you could counter argue that noone calls it that way today.

In that sense, I am fine with this, just wanted to report the gap after 
this patch before I ack.

>> OR you can even add that line in the if (ret) of 
>> msm_dsi_manager_ext_bridge_init(msm_dsi->id); failure.
>>
>>>>
>>>>> -
>>>>> -    return ret;
>>>>>   }
>>>>>   void msm_dsi_snapshot(struct msm_disp_state *disp_state, struct 
>>>>> msm_dsi *msm_dsi)
>>>>> diff --git a/drivers/gpu/drm/msm/dsi/dsi.h 
>>>>> b/drivers/gpu/drm/msm/dsi/dsi.h
>>>>> index d21867da78b8..a01c326774a6 100644
>>>>> --- a/drivers/gpu/drm/msm/dsi/dsi.h
>>>>> +++ b/drivers/gpu/drm/msm/dsi/dsi.h
>>>>> @@ -56,8 +56,7 @@ struct msm_dsi {
>>>>>   };
>>>>>   /* dsi manager */
>>>>> -struct drm_bridge *msm_dsi_manager_bridge_init(u8 id);
>>>>> -void msm_dsi_manager_bridge_destroy(struct drm_bridge *bridge);
>>>>> +int msm_dsi_manager_bridge_init(struct msm_dsi *msm_dsi);
>>>>>   int msm_dsi_manager_ext_bridge_init(u8 id);
>>>>>   int msm_dsi_manager_cmd_xfer(int id, const struct mipi_dsi_msg 
>>>>> *msg);
>>>>>   bool msm_dsi_manager_cmd_xfer_trigger(int id, u32 dma_base, u32 
>>>>> len);
>>>>> diff --git a/drivers/gpu/drm/msm/dsi/dsi_manager.c 
>>>>> b/drivers/gpu/drm/msm/dsi/dsi_manager.c
>>>>> index 28b8012a21f2..17aa19bb6510 100644
>>>>> --- a/drivers/gpu/drm/msm/dsi/dsi_manager.c
>>>>> +++ b/drivers/gpu/drm/msm/dsi/dsi_manager.c
>>>>> @@ -466,9 +466,8 @@ static const struct drm_bridge_funcs 
>>>>> dsi_mgr_bridge_funcs = {
>>>>>   };
>>>>>   /* initialize bridge */
>>>>> -struct drm_bridge *msm_dsi_manager_bridge_init(u8 id)
>>>>> +int msm_dsi_manager_bridge_init(struct msm_dsi *msm_dsi)
>>>>>   {
>>>>> -    struct msm_dsi *msm_dsi = dsi_mgr_get_dsi(id);
>>>>>       struct drm_bridge *bridge = NULL;
>>>>>       struct dsi_bridge *dsi_bridge;
>>>>>       struct drm_encoder *encoder;
>>>>> @@ -476,31 +475,27 @@ struct drm_bridge 
>>>>> *msm_dsi_manager_bridge_init(u8 id)
>>>>>       dsi_bridge = devm_kzalloc(msm_dsi->dev->dev,
>>>>>                   sizeof(*dsi_bridge), GFP_KERNEL);
>>>>> -    if (!dsi_bridge) {
>>>>> -        ret = -ENOMEM;
>>>>> -        goto fail;
>>>>> -    }
>>>>> +    if (!dsi_bridge)
>>>>> +        return -ENOMEM;
>>>>> -    dsi_bridge->id = id;
>>>>> +    dsi_bridge->id = msm_dsi->id;
>>>>>       encoder = msm_dsi->encoder;
>>>>>       bridge = &dsi_bridge->base;
>>>>>       bridge->funcs = &dsi_mgr_bridge_funcs;
>>>>> -    drm_bridge_add(bridge);
>>>>> +    ret = devm_drm_bridge_add(&msm_dsi->pdev->dev, bridge);
>>>>> +    if (ret)
>>>>> +        return ret;
>>>>>       ret = drm_bridge_attach(encoder, bridge, NULL, 0);
>>>>>       if (ret)
>>>>> -        goto fail;
>>>>> +        return ret;
>>>>> -    return bridge;
>>>>> +    msm_dsi->bridge = bridge;
>>>>> -fail:
>>>>> -    if (bridge)
>>>>> -        msm_dsi_manager_bridge_destroy(bridge);
>>>>> -
>>>>> -    return ERR_PTR(ret);
>>>>> +    return 0;
>>>>>   }
>>>>>   int msm_dsi_manager_ext_bridge_init(u8 id)
>>>>> @@ -557,11 +552,6 @@ int msm_dsi_manager_ext_bridge_init(u8 id)
>>>>>       return 0;
>>>>>   }
>>>>> -void msm_dsi_manager_bridge_destroy(struct drm_bridge *bridge)
>>>>> -{
>>>>> -    drm_bridge_remove(bridge);
>>>>> -}
>>>>> -
>>>>>   int msm_dsi_manager_cmd_xfer(int id, const struct mipi_dsi_msg *msg)
>>>>>   {
>>>>>       struct msm_dsi *msm_dsi = dsi_mgr_get_dsi(id);
>>>
>