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

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Date:   Tue, 2 Jan 2018 18:32:11 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Thierry Reding <thierry.reding@...il.com>,
        Guillaume Tucker <guillaume.tucker@...labora.com>,
        Peter De Schrijver <pdeschrijver@...dia.com>
CC:     Thierry Reding <treding@...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 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).

Cheers
Jon

-- 
nvpublic