linux-kernel - Re: [RESEND PATCH 1/2] devicetree: mxsfb: add reset-active property

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Date:	Tue, 12 Jan 2016 15:39:06 +0200
From:	Tomi Valkeinen <tomi.valkeinen@...com>
To:	Måns Rullgård <mans@...sr.com>
CC:	Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-fbdev@...r.kernel.org>
Subject: Re: [RESEND PATCH 1/2] devicetree: mxsfb: add reset-active property



On 12/01/16 15:10, Måns Rullgård wrote:

>> I don't see any sleeps related to reset in the code. If reset is
>> asserted when the display is blanked, is it guaranteed that the reset
>> stays asserted long enough until the display is enabled again?
> 
> In the datasheet for the panel I'm dealing with, there's some vague
> mention of 10 us (I missed it last time I looked), and my patch indeed
> fails to ensure this is met.  Other panels will obviously have different
> requirements.  To handle all cases properly, I suppose a configurable
> delay after changing the reset pin should be added.

Right. And then you need to ensure the powers are enabled in the right
order, the pixel clock is started at the right time (some need pix clock
before reset), and so on and so on =).

> I could also take the lazy way out, pinmux this signal high and leave it
> at that.

I've seen panels that require a reset after powers have been off, or
similar, but I hope those are minority.

So yes, probably just making sure the reset is not asserted is the most
generic and easy way forward.

 Tomi


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