Assert DisplayPort reset signal before deasserting,
it is to clear out any registers programmed before booting kernel.

Signed-off-by: Rohit Visavalia <rohit.visavalia@amd.com>
---
 drivers/gpu/drm/xlnx/zynqmp_dp.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c b/drivers/gpu/drm/xlnx/zynqmp_dp.c
index 1846c4971fd8..5a40aa1d4283 100644
--- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
+++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
@@ -1714,6 +1714,10 @@ int zynqmp_dp_probe(struct zynqmp_dpsub *dpsub)
 		goto err_free;
 	}
 
+	ret = zynqmp_dp_reset(dp, true);
+	if (ret < 0)
+		return ret;
+
 	ret = zynqmp_dp_reset(dp, false);
 	if (ret < 0)
 		goto err_free;
-- 
2.25.1

Hello Rohit,

Thank you for the patch.

On Fri, Feb 16, 2024 at 04:40:43AM -0800, Rohit Visavalia wrote:
> Assert DisplayPort reset signal before deasserting,
> it is to clear out any registers programmed before booting kernel.
> 
> Signed-off-by: Rohit Visavalia <rohit.visavalia@amd.com>
> ---
>  drivers/gpu/drm/xlnx/zynqmp_dp.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> index 1846c4971fd8..5a40aa1d4283 100644
> --- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
> +++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> @@ -1714,6 +1714,10 @@ int zynqmp_dp_probe(struct zynqmp_dpsub *dpsub)
>  		goto err_free;
>  	}
>  
> +	ret = zynqmp_dp_reset(dp, true);
> +	if (ret < 0)
> +		return ret;
> +

This looks fine to me, so

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

However, looking at zynqmp_dp_reset(), we have

static int zynqmp_dp_reset(struct zynqmp_dp *dp, bool assert)
{
	unsigned long timeout;

	if (assert)
		reset_control_assert(dp->reset);
	else
		reset_control_deassert(dp->reset);

	/* Wait for the (de)assert to complete. */
	timeout = jiffies + msecs_to_jiffies(RST_TIMEOUT_MS);
	while (!time_after_eq(jiffies, timeout)) {
		bool status = !!reset_control_status(dp->reset);

		if (assert == status)
			return 0;

		cpu_relax();
	}

	dev_err(dp->dev, "reset %s timeout\n", assert ? "assert" : "deassert");
	return -ETIMEDOUT;
}

That doesn't seem quite right. Aren't reset_control_assert() and
reset_control_deassert() supposed to be synchronous ? If so there should
be no need to wait, and if there's a need to wait, it could be a bug in
the reset controller driver. This should be fixed, and then the code in
probe could be replaced with a call to reset_control_reset().

>  	ret = zynqmp_dp_reset(dp, false);
>  	if (ret < 0)
>  		goto err_free;

-- 
Regards,

Laurent Pinchart

Tomi, could you push this through drm-misc ?

On Wed, Feb 28, 2024 at 06:22:25PM +0200, Laurent Pinchart wrote:
> Hello Rohit,
> 
> Thank you for the patch.
> 
> On Fri, Feb 16, 2024 at 04:40:43AM -0800, Rohit Visavalia wrote:
> > Assert DisplayPort reset signal before deasserting,
> > it is to clear out any registers programmed before booting kernel.
> > 
> > Signed-off-by: Rohit Visavalia <rohit.visavalia@amd.com>
> > ---
> >  drivers/gpu/drm/xlnx/zynqmp_dp.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> > index 1846c4971fd8..5a40aa1d4283 100644
> > --- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
> > +++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> > @@ -1714,6 +1714,10 @@ int zynqmp_dp_probe(struct zynqmp_dpsub *dpsub)
> >  		goto err_free;
> >  	}
> >  
> > +	ret = zynqmp_dp_reset(dp, true);
> > +	if (ret < 0)
> > +		return ret;
> > +
> 
> This looks fine to me, so
> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> 
> However, looking at zynqmp_dp_reset(), we have
> 
> static int zynqmp_dp_reset(struct zynqmp_dp *dp, bool assert)
> {
> 	unsigned long timeout;
> 
> 	if (assert)
> 		reset_control_assert(dp->reset);
> 	else
> 		reset_control_deassert(dp->reset);
> 
> 	/* Wait for the (de)assert to complete. */
> 	timeout = jiffies + msecs_to_jiffies(RST_TIMEOUT_MS);
> 	while (!time_after_eq(jiffies, timeout)) {
> 		bool status = !!reset_control_status(dp->reset);
> 
> 		if (assert == status)
> 			return 0;
> 
> 		cpu_relax();
> 	}
> 
> 	dev_err(dp->dev, "reset %s timeout\n", assert ? "assert" : "deassert");
> 	return -ETIMEDOUT;
> }
> 
> That doesn't seem quite right. Aren't reset_control_assert() and
> reset_control_deassert() supposed to be synchronous ? If so there should
> be no need to wait, and if there's a need to wait, it could be a bug in
> the reset controller driver. This should be fixed, and then the code in
> probe could be replaced with a call to reset_control_reset().
> 
> >  	ret = zynqmp_dp_reset(dp, false);
> >  	if (ret < 0)
> >  		goto err_free;

-- 
Regards,

Laurent Pinchart

On 29/02/2024 11:05, Laurent Pinchart wrote:
> Tomi, could you push this through drm-misc ?
> 
> On Wed, Feb 28, 2024 at 06:22:25PM +0200, Laurent Pinchart wrote:
>> Hello Rohit,
>>
>> Thank you for the patch.
>>
>> On Fri, Feb 16, 2024 at 04:40:43AM -0800, Rohit Visavalia wrote:
>>> Assert DisplayPort reset signal before deasserting,
>>> it is to clear out any registers programmed before booting kernel.
>>>
>>> Signed-off-by: Rohit Visavalia <rohit.visavalia@amd.com>
>>> ---
>>>   drivers/gpu/drm/xlnx/zynqmp_dp.c | 4 ++++
>>>   1 file changed, 4 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c b/drivers/gpu/drm/xlnx/zynqmp_dp.c
>>> index 1846c4971fd8..5a40aa1d4283 100644
>>> --- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
>>> +++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
>>> @@ -1714,6 +1714,10 @@ int zynqmp_dp_probe(struct zynqmp_dpsub *dpsub)
>>>   		goto err_free;
>>>   	}
>>>   
>>> +	ret = zynqmp_dp_reset(dp, true);
>>> +	if (ret < 0)
>>> +		return ret;
>>> +
>>
>> This looks fine to me, so
>>
>> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
>>

Thanks, tested and pushed to drm-misc-next.

  Tomi