linux-kernel - Re: [PATCH] omapdss: Add new panel driver for Topolly td028ttec1 LCD.

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Message-ID: <5257815F.5070803@ti.com>
Date:	Fri, 11 Oct 2013 07:41:03 +0300
From:	Tomi Valkeinen <tomi.valkeinen@...com>
To:	Lars-Peter Clausen <lars@...afoo.de>,
	"Dr. H. Nikolaus Schaller" <hns@...delico.com>
CC:	Marek Belisko <marek@...delico.com>, <plagnioj@...osoft.com>,
	<linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<linux-fbdev@...r.kernel.org>
Subject: Re: [PATCH] omapdss: Add new panel driver for Topolly td028ttec1
 LCD.

On 10/10/13 21:58, Lars-Peter Clausen wrote:

> According to the datasheet the the panel as a dedicated dout pin. Maybe
> you did not connect it in your design, which means you won't be able to
> read any data from the panel at all.

I don't see a dedicated dout in the datasheet...
http://dl.wolfgang-draxinger.net/openmoko/doc/TD028TTEC1.pdf

> Also your custom bitbang code looks a bit strange:
> 
>     gpio_set_value(data->dout_gpio, 1);
>     if (gpio_get_value(data->din_gpio) == 0)
>         return 1;
> 
> You set the state on the dout pin and then read the din pin, if both do
> not match you abort with an error. This suggest that, for whatever
> reason, you feed the dout pin back into the din pin in your design. Btw.
> this is also the only place where din is used in your driver.

Yes, he said the single "Serial interface data input/output" pin is
connected to both din and dout on the SoC. I guess the purpose of that
gpio_get_value() is to ensure that the panel is not pulling the line
when the SoC is writing to it. Not that I really understand how that can
work, but I'm not a HW guy =).

 Tomi



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