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

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Message-Id: <AB436C46-413A-4469-BA07-F3ED1CECF02F@goldelico.com>
Date:   Sat, 16 Sep 2023 14:50:24 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
        Tony Lindgren <tony@...mide.com>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Sebastian Reichel <sre@...nel.org>,
        dri-devel@...ts.freedesktop.org, linux-omap@...r.kernel.org,
        linux-kernel@...r.kernel.org, Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...il.com>
Subject: Re: [PATCH] drm/omap: dsi: Fix deferred probe warnings

Hi Tomi and Tony,

> Am 13.09.2023 um 13:59 schrieb Tomi Valkeinen <tomi.valkeinen@...asonboard.com>:
> 
> On 12/04/2023 10:39, 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.
>> 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);
> 
> Shouldn't this rather be
> 
> if (!dsi->dsidev)
> 	return 0;
> 
> before the if (WARN_ON(dsi->dsidev != client)) line?

Yes you are right. We have a different variant in our Pyra kernel:

What we currently have in our Pyra tree is: https://git.goldelico.com/?p=letux-kernel.git;a=commitdiff;h=5bf7bd64eec1eb924e794e8d6600919f0dae8c5a;hp=27a0cd6263194d1465e9c53293d35f8c8c988f9d

        struct dsi_data *dsi = host_to_omap(host);
 
-       if (WARN_ON(dsi->dsidev != client))
+printk("%s\n", __func__);
+
+       if (!dsi->dsidev || WARN_ON(dsi->dsidev != client))
                return -EINVAL;
 
        cancel_delayed_work_sync(&dsi->dsi_disable_work);

> 
> If dsi->dsidev is NULL, then attach hasn't been called, and we shouldn't do anything in the detach callback either.
> 
> With your change we'll end up doing all the work in the detach callback, without ever doing their counterpart in the attach side.

If useful, I can post above mentioned patch (without printk).

BR and thanks,
Nikolaus