linux-kernel - Re: [PATCH v5 07/13] drm/bridge: cdns-dsi: Wait for Clk and Data Lanes to be ready

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Message-ID: <36128d71-a600-4c33-97f6-e694e493b3ee@linux.dev>
Date: Tue, 22 Oct 2024 22:55:38 +0530
From: Aradhya Bhatia <aradhya.bhatia@...ux.dev>
To: Devarsh Thakkar <devarsht@...com>,
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
 Laurent Pinchart <laurent.pinchart@...asonboard.com>,
 Andrzej Hajda <andrzej.hajda@...el.com>,
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>,
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Cc: Dominik Haller <d.haller@...tec.de>, Sam Ravnborg <sam@...nborg.org>,
 Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
 Nishanth Menon <nm@...com>, Vignesh Raghavendra <vigneshr@...com>,
 Praneeth Bajjuri <praneeth@...com>, Udit Kumar <u-kumar1@...com>,
 Jayesh Choudhary <j-choudhary@...com>,
 DRI Development List <dri-devel@...ts.freedesktop.org>,
 Linux Kernel List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 07/13] drm/bridge: cdns-dsi: Wait for Clk and Data
 Lanes to be ready



On 22/10/24 11:55, Devarsh Thakkar wrote:
> Hi Aradhya,
> 
> Thanks for the patch.
> 
> On 20/10/24 01:24, Aradhya Bhatia wrote:
>> From: Aradhya Bhatia <a-bhatia1@...com>
> 
> [...]
> 
>> +	/*
>> +	 * Now that the DSI Link and DSI Phy are initialized,
>> +	 * wait for the CLK and Data Lanes to be ready.
>> +	 */
>> +	tmp = CLK_LANE_RDY;
>> +	for (int i = 0; i < nlanes; i++)
>> +		tmp |= DATA_LANE_RDY(i);
>> +
>> +	if (readl_poll_timeout(dsi->regs + MCTL_MAIN_STS, status,
>> +			       status & tmp, 100, 500000))
> 
> The above would mark the condition as true even if one data lane gets ready. I
> think we need to poll until all data lanes are marked as ready. Also good to
> give a warning in case we time out.
> 
> IMHO below should fix this:
>         WARN_ON_ONCE(readl_poll_timeout(dsi->regs + MCTL_MAIN_STS, status,
>                                        (tmp == (status & tmp)), 100, 0));
> 

That's how the condition should be, yes! Thanks for the catch!

I would still prefer to keep dev_err instead of WARN_ON_ONCE, because
the latter stack-dumps during boot once, and then can never be seen
again during multiple modesets. The noise in the dmesg is not worth
the issue either.

With dev_err, it can show a clear print once every time it times out.

-- 
Regards
Aradhya