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

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Date:	Fri, 11 Oct 2013 10:59:29 +0200
From:	Belisko Marek <marek.belisko@...il.com>
To:	Tomi Valkeinen <tomi.valkeinen@...com>
Cc:	"Dr. H. Nikolaus Schaller" <hns@...delico.com>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Jean-Christophe PLAGNIOL-VILLARD <plagnioj@...osoft.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-omap@...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.

Hi Tomi,

On Fri, Oct 11, 2013 at 10:17 AM, Tomi Valkeinen <tomi.valkeinen@...com> wrote:
> On 11/10/13 10:42, Dr. H. Nikolaus Schaller wrote:
>
>> I am not sure if there is a SPI driver for a McBSP port [1]? And to make that
>> work (reliably) and tested it might need a lot of work for us. At least I think
>> such a change (e.g. setting up clock polarity etc.) is not done in some minutes.
>> And the only feedback we have from the panel is "does not work"/"works". I.e.
>> if we are not lucky that it works immediately we have no real means to debug.
>>
>> IMHO it also gives more flexibility to board designers to choose GPIOs instead
>> of enforcing some SPI interface by the driver (and encapsulate this arguable
>> protocol in the driver). Maybe some board has 3 spare GPIOs but neither
>> McBSPs nor McSPIs available.
>
> This has been an interesting thread, I've learnt a lot =).
>
> I still think the panel driver should not handle this, but there should
> be a separate spi bitbang driver for it.
>
> I understand you're not enthusiastic going that way, as the current
> version works for you. However, when using DT, we need to think how to
> represent the hardware in the device tree data, and it has to be right
> from the beginning.
>
> That's why I won't allow representing this panel as having 4 gpios in
> the DT data, because that is not correct. The panel has 3 pins. But
> then, the panel does allow reading, which could be implemented using 4
> gpios as you have done. This data should be in the spi-bitbang data, and
> the panel should just use the standard SPI framework.
I disagree. There are different drivers which pass in platform data
gpios (encoder-tfp410.c or encoder-tpd12s015.c)
and those must be covered by DT then. I cannot see problem why to have
for td028 panel 3 or 4 gpios defined in DT.
>
> Using SPI framework does not mean you should use McBSP or McSPI. It's up
> to you how the 3-wire SPI is implemented on the SoC side, the panel
> would just work in all the cases.
>
>  Tomi
>
>

BR,

marek

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