linux-kernel - Re: [PATCH] drm: xlnx: dp: Reset DisplayPort IP

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Message-ID: <20240229090511.GG1659@pendragon.ideasonboard.com>
Date: Thu, 29 Feb 2024 11:05:11 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc: Rohit Visavalia <rohit.visavalia@....com>,
	maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
	tzimmermann@...e.de, airlied@...il.com, daniel@...ll.ch,
	michal.simek@....com, dri-devel@...ts.freedesktop.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm: xlnx: dp: Reset DisplayPort IP

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@....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@...asonboard.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