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

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Message-ID: <e9c2e179-eacc-151e-123b-a4e425e76333@collabora.com>
Date:   Mon, 17 Apr 2023 11:44:00 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     neil.armstrong@...aro.org,
        Konrad Dybcio <konrad.dybcio@...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 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.

Regards,
Angelo