linux-kernel - Re: [PATCH] drm/panel: novatek-nt35950: Improve error handling

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Message-ID: <3570a98d-a7f8-7bef-0184-ad740cc44ee6@collabora.com>
Date:   Mon, 17 Apr 2023 16:16:14 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>,
        neil.armstrong@...aro.org, Sam Ravnborg <sam@...nborg.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>
Cc:     Marijn Suijten <marijn.suijten@...ainline.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panel: novatek-nt35950: Improve error handling

Il 17/04/23 15:38, Konrad Dybcio ha scritto:
> 
> 
> On 17.04.2023 11:44, AngeloGioacchino Del Regno wrote:
>> Il 17/04/23 11:44, AngeloGioacchino Del Regno ha scritto:
>>> Il 17/04/23 09:25, Neil Armstrong ha scritto:
>>>> On 15/04/2023 13:00, Konrad Dybcio wrote:
>>>>> In a very peculiar case when probing and registering with the secondary
>>>>> DSI host succeeds, but the OF backlight or DSI attachment fails, the
>>>>> primary DSI device is automatically cleaned up, but the secondary one
>>>>> is not, leading to -EEXIST when the driver core tries to handle
>>>>> -EPROBE_DEFER.
>>>>>
>>>>> Unregister the DSI1 device manually on failure to prevent that.
>>>>>
>>>>> Fixes: 623a3531e9cf ("drm/panel: Add driver for Novatek NT35950 DSI DriverIC panels")
>>>>> Signed-off-by: Konrad Dybcio <konrad.dybcio@...aro.org>
>>>>> ---
>>>>>    drivers/gpu/drm/panel/panel-novatek-nt35950.c | 8 +++++++-
>>>>>    1 file changed, 7 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/panel/panel-novatek-nt35950.c b/drivers/gpu/drm/panel/panel-novatek-nt35950.c
>>>>> index abf752b36a52..7498fc6258bb 100644
>>>>> --- a/drivers/gpu/drm/panel/panel-novatek-nt35950.c
>>>>> +++ b/drivers/gpu/drm/panel/panel-novatek-nt35950.c
>>>>> @@ -585,8 +585,11 @@ static int nt35950_probe(struct mipi_dsi_device *dsi)
>>>>>                   DRM_MODE_CONNECTOR_DSI);
>>>>>        ret = drm_panel_of_backlight(&nt->panel);
>>>>> -    if (ret)
>>>>> +    if (ret) {
>>>
>>> If this is not a dual-DSI case, nt->dsi[1] will be NULL: I agree it's still
>>> fine as in the kernel won't crash in that case, but for logical correctness
>>> I would still account for that:
>>>
>>>           if (num_dsis == 2)
>>>               mipi_dsi_device_unregister(nt->dsi[1]);
>>>
>>>>> +        mipi_dsi_device_unregister(nt->dsi[1]);
>>>>> +
>>>>>            return dev_err_probe(dev, ret, "Failed to get backlight\n");
>>>>> +    }
>>>>>        drm_panel_add(&nt->panel);
>>>>> @@ -602,6 +605,9 @@ static int nt35950_probe(struct mipi_dsi_device *dsi)
>>>>>            ret = mipi_dsi_attach(nt->dsi[i]);
>>>>>            if (ret < 0) {
>>>
>>> Same here, please add a check for num_dsis.
> Right, I'll send an incremental patch to fix the fix, thanks
> for spotting this!
> 

You're welcome! Please make sure to Cc me so that I can timely give you a review!

Cheers,
Angelo