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

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Message-ID: <20230913073755.GE5285@atomide.com>
Date:   Wed, 13 Sep 2023 10:37:55 +0300
From:   Tony Lindgren <tony@...mide.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
        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

* Laurent Pinchart <laurent.pinchart@...asonboard.com> [230412 11:59]:
> On Wed, Apr 12, 2023 at 11:55:34AM +0300, Tomi Valkeinen wrote:
> > 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.
> 
> Is this something that should be addressed in the DRM MIPI DSI helpers,
> to only detach after an attach ?

Tomi, any comments on detach after attach?

Regards,

Tony

> > >> 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);
> 
> -- 
> Regards,
> 
> Laurent Pinchart
>