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

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Date:   Wed, 20 Dec 2017 19:15:20 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Guillaume Tucker <guillaume.tucker@...labora.com>
Cc:     Thierry Reding <treding@...dia.com>,
        Jon Hunter <jonathanh@...dia.com>,
        Peter De Schrijver <pdeschrijver@...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 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.

Thierry

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