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

[Dmitry Osipenko]

On 9/24/18 3:32 PM, Jon Hunter wrote:
> 
> On 24/09/18 12:59, Thierry Reding wrote:
>> 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 at vger.kernel.org> # v4.8+
>>> Signed-off-by: Dmitry Osipenko <digetx at 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.
> 
> Did you change the subject for the patch because as you mentioned it
> does not seem related to the change?
> 
> Otherwise for the fix you can have my ...
> 
> Acked-by: Jon Hunter <jonathanh at nvidia.com>
> 
> The dpaux driver has been working fine for me on Tegra210 Smaug when
> using the pins for I2C and I have not seen any probing problems.

Guy with nickname "vlado" said on the IRC that the panel stopped to work on T124 
chromebook since 4.16 kernel, reverting commit [0] helps.

[0] 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/gpu/drm/drm_dp_helper.c?id=17ab7806de0c10d27cdbda8ef57ca680bdd24315