Re: [PATCH v1] drm/tegra: dpaux: Fix always-failing probing of the driver

From: Thierry Reding <thierry.reding@gmail.com>
To: Dmitry Osipenko <digetx@gmail.com>
Cc: linux-tegra@vger.kernel.org, dri-devel@lists.freedesktop.org,
	Jonathan Hunter <jonathanh@nvidia.com>
Subject: Re: [PATCH v1] drm/tegra: dpaux: Fix always-failing probing of the driver
Date: Mon, 24 Sep 2018 13:59:07 +0200	[thread overview]
Message-ID: <20180924115907.GW21032@ulmo> (raw)
In-Reply-To: <20180921114241.17002-1-digetx@gmail.com>

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On Fri, Sep 21, 2018 at 02:42:41PM +0300, Dmitry Osipenko wrote:
> Some of definitions in the code changed the meaning, unfortunately one
> place missed the change.
> 
> Fixes: 0751bb5c44fe ("drm/tegra: dpaux: Add pinctrl support")
> Cc: <stable@vger.kernel.org> # v4.8+
> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
> ---
> 
> I don't have HW to test DPAUX driver, apparently it has been broken for
> 2+ years now. There is also a known issue on with the DPAUX driver that
> prevents it from probing, that was discussed on the #tegra IRC. Thierry,
> please take a closer look at this driver and test it thoroughly, it has
> some obvious problems.
> 
>  drivers/gpu/drm/tegra/dpaux.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

It's odd that you claim that the driver is always failing probe and at
the same time you say that you don't have hardware to test the driver.
=)

I know for a fact that this driver does not usually fail because it is
required on all recent chips (Tegra210 and later) to drive HDMI, which
we support on all boards, so it is indeed thoroughly tested.

> 
> diff --git a/drivers/gpu/drm/tegra/dpaux.c b/drivers/gpu/drm/tegra/dpaux.c
> index d84e81ff36ad..ba5681fab73b 100644
> --- a/drivers/gpu/drm/tegra/dpaux.c
> +++ b/drivers/gpu/drm/tegra/dpaux.c
> @@ -521,7 +521,7 @@ static int tegra_dpaux_probe(struct platform_device *pdev)
>  	 * is no possibility to perform the I2C mode configuration in the
>  	 * HDMI path.
>  	 */
> -	err = tegra_dpaux_pad_config(dpaux, DPAUX_HYBRID_PADCTL_MODE_I2C);
> +	err = tegra_dpaux_pad_config(dpaux, DPAUX_PADCTL_FUNC_I2C);
>  	if (err < 0)
>  		return err;
>  

If you look at the definitions of both DPAUX_HYBRID_PADCTL_MODE_I2C and
DPAUX_PADCTL_FUNC_I2C, you'll see that both are actually the same, which
is a good explanation for why the driver performs flawlessly.

That said, your change is obviously correct. I've applied it, but since
it doesn't actually fix anything, and doesn't change anything from a
binary point of view, I've removed the Fixes: and Cc: stable tags.

Thanks,
Thierry

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