linux-kernel - Re: [RFC PATCH v2 1/1] drm/tegra: sor: Fix hang on tegra124 due to NULL clk

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Message-ID: <20180110121334.GA25824@ulmo>
Date:   Wed, 10 Jan 2018 13:13:34 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Jon Hunter <jonathanh@...dia.com>
Cc:     Guillaume Tucker <guillaume.tucker@...labora.com>,
        Peter De Schrijver <pdeschrijver@...dia.com>,
        Thierry Reding <treding@...dia.com>,
        David Airlie <airlied@...ux.ie>, linux-tegra@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 1/1] drm/tegra: sor: Fix hang on tegra124 due to
 NULL clk_out

On Tue, Jan 02, 2018 at 06:32:11PM +0000, Jon Hunter wrote:
> 
> On 20/12/17 18:15, Thierry Reding wrote:
> > On Wed, Dec 20, 2017 at 11:32:23AM +0000, Guillaume Tucker wrote:
> >> When neither HDMI nor DP is supported such as on the tegra124, the
> >> sor->clk_out is not initialised and remains NULL.  In this case, the
> >> parent clock can't be assigned to it so revert to the previous
> >> behaviour of assigning it to the main sor->clk instead.
> >>
> >> This fixes a kernel hang on tegra124 and should also affect tegra210
> >> as they both don't support HDMI and DP.  Tested on tegra124 only.
> >>
> >> Fixes: e1335e2f0cfc ("drm/tegra: sor: Reimplement pad clock")
> >> Signed-off-by: Guillaume Tucker <guillaume.tucker@...labora.com>
> >> CC: Thierry Reding <treding@...dia.com>
> >> ---
> >>  drivers/gpu/drm/tegra/sor.c | 2 +-
> >>  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > How about just the below instead? It's one more line than your patch,
> > but it will automatically handle all occurrences of clk_out properly.
> > 
> > --- >8 ---
> > diff --git a/drivers/gpu/drm/tegra/sor.c b/drivers/gpu/drm/tegra/sor.c
> > index f6313c4d612e..4be9edf9c6fe 100644
> > --- a/drivers/gpu/drm/tegra/sor.c
> > +++ b/drivers/gpu/drm/tegra/sor.c
> > @@ -3047,6 +3047,8 @@ static int tegra_sor_probe(struct platform_device *pdev)
> >                                 name, err);
> >                         goto remove;
> >                 }
> > +       } else {
> > +               sor->clk_out = sor->clk;
> >         }
> >  
> >         sor->clk_parent = devm_clk_get(&pdev->dev, "parent");
> > --- >8 ---
> > 
> > That said, I suspect the SOR might be compatible from a clock point of
> > view with later versions and perhaps we just didn't implement clocks
> > correctly back in the Tegra124 timeframe.
> > 
> > Maybe Peter knows.
> 
> So the above change from Thierry works for me and we need this for v4.15
> (otherwise nyan-big does not boot) so you can have my ...
> 
> Tested-by: Jon Hunter <jonathanh@...dia.com>
> 
> However, would be good to have Peter's ACK, especially seeing that
> Tegra210 sor0 does not support HDMI and DP. So we need to make sure this
> is correct for Tegra210 as well (although I have not seen any
> regressions for Tegra210).

There are no Tegra210 boards with eDP or LVDS support, which are the
only setups that are impacted by this.

I've sent out the above as a proper patch. I'll submit this for a late
fixes pull request.

Thierry

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