linux-kernel - Re: [PATCH v3 3/4] drm/msm: add a kernel param to select between MDP5 and DPU drivers

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Date: Tue, 9 Jan 2024 11:32:19 -0800
From: Carl Vanderlip <quic_carlv@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC: Rob Clark <robdclark@...il.com>,
        Abhinav Kumar
	<quic_abhinavk@...cinc.com>,
        Sean Paul <sean@...rly.run>,
        Marijn Suijten
	<marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, "Daniel
 Vetter" <daniel@...ll.ch>,
        <linux-arm-msm@...r.kernel.org>, <freedreno@...ts.freedesktop.org>,
        <linux-kernel@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        Stephen Boyd <swboyd@...omium.org>
Subject: Re: [PATCH v3 3/4] drm/msm: add a kernel param to select between MDP5
 and DPU drivers

On 1/8/2024 11:07 AM, Dmitry Baryshkov wrote:
> On Mon, 8 Jan 2024 at 19:57, Carl Vanderlip <quic_carlv@...cinc.com> wrote:
>> On 1/5/2024 4:38 PM, Dmitry Baryshkov wrote:
>>> On Sat, 6 Jan 2024 at 02:04, Carl Vanderlip <quic_carlv@...cinc.com> wrote:
>>>> On 1/5/2024 3:34 PM, Dmitry Baryshkov wrote:
>>>>> diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
>>>>> index 50b65ffc24b1..ef57586fbeca 100644
>>>>> --- a/drivers/gpu/drm/msm/msm_drv.c
>>>>> +++ b/drivers/gpu/drm/msm/msm_drv.c
>>>>> @@ -969,6 +969,37 @@ static int add_components_mdp(struct device *master_dev,
>>>>>         return 0;
>>>>>     }
>>>>>
>>>>> +#if !IS_REACHABLE(CONFIG_DRM_MSM_MDP5) || !IS_REACHABLE(CONFIG_DRM_MSM_DPU)
>>>>> +bool msm_disp_drv_should_bind(struct device *dev, bool mdp5_driver)
>>>>> +{
>>>>> +     /* If just a single driver is enabled, use it no matter what */
>>>>> +     return true;
>>>>> +}
>>>>
>>>> This will cause both MDP/DPU probes to return -ENODEV, rather than
>>>> select the enabled one.
>>>
>>> No. The code (e.g. for DPU) is:
>>>
>>>          if (!msm_disp_drv_should_bind(&pdev->dev, true))
>>>                   return -ENODEV;
>>>
>>> So the driver returns -ENODEV if msm_disp_drv_should_bind() returns
>>> false. Which is logical from the function name point of view.
>>>
>>
>> but msm_disp_drv_should_bind() is returning true in the #if !REACHABLE()
>> case?
>>
>> at minimum the comment is incorrect since returning true causes the
>> driver to NOT be used.
> 
> No. Returning _false_ causes the driver to not be used.
> 

Apologies... you are correct.

Reviewed-by: Carl Vanderlip <quic_carlv@...cinc.com>

-Carl V.