linux-kernel - Re: [PATCH] drm/omap: dsi: Fix deferred probe warnings

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Message-ID: <2bf56c04-733b-24a5-a344-166a94cd51f7@ideasonboard.com>
Date:   Wed, 12 Apr 2023 11:55:34 +0300
From:   Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Tony Lindgren <tony@...mide.com>
Cc:     David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Sebastian Reichel <sre@...nel.org>,
        dri-devel@...ts.freedesktop.org, linux-omap@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/omap: dsi: Fix deferred probe warnings

On 12/04/2023 11:50, Laurent Pinchart wrote:
> Hi Tony,
> 
> Thank you for the patch.
> 
> On Wed, Apr 12, 2023 at 10:39:53AM +0300, Tony Lindgren wrote:
>> We may not have dsi->dsidev initialized during probe, and that can
>> lead into various dsi related warnings as omap_dsi_host_detach() gets
>> called with dsi->dsidev set to NULL.
>>
>> The warnings can be "Fixed dependency cycle(s)" followed by a
>> WARNING: CPU: 0 PID: 787 at drivers/gpu/drm/omapdrm/dss/dsi.c:4414.
> 
> How can this happen ? I assume .detach() can't be called without a
> priori successful call to .attach(), that that sets dsi->dsidev.

I had a quick look, and the driver calls mipi_dsi_host_register() in 
probe, and mipi_dsi_host_unregister() in remove.

mipi_dsi_host_unregister() always calls mipi_dsi_detach(), but I don't 
think mipi_dsi_host_register() always calls attach, which happens later 
when the peripheral probes.

  Tomi

>> Let's fix the warnings by checking for a valid dsi->dsidev.
>>
>> Signed-off-by: Tony Lindgren <tony@...mide.com>
>> ---
>>   drivers/gpu/drm/omapdrm/dss/dsi.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/omapdrm/dss/dsi.c b/drivers/gpu/drm/omapdrm/dss/dsi.c
>> --- a/drivers/gpu/drm/omapdrm/dss/dsi.c
>> +++ b/drivers/gpu/drm/omapdrm/dss/dsi.c
>> @@ -4411,7 +4411,7 @@ static int omap_dsi_host_detach(struct mipi_dsi_host *host,
>>   {
>>   	struct dsi_data *dsi = host_to_omap(host);
>>   
>> -	if (WARN_ON(dsi->dsidev != client))
>> +	if (dsi->dsidev && WARN_ON(dsi->dsidev != client))
>>   		return -EINVAL;
>>   
>>   	cancel_delayed_work_sync(&dsi->dsi_disable_work);
>