Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756890Ab3JKKJk (ORCPT ); Fri, 11 Oct 2013 06:09:40 -0400 Received: from comal.ext.ti.com ([198.47.26.152]:33726 "EHLO comal.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755234Ab3JKKJh (ORCPT ); Fri, 11 Oct 2013 06:09:37 -0400 Message-ID: <5257CE55.3090902@ti.com> Date: Fri, 11 Oct 2013 13:09:25 +0300 From: Tomi Valkeinen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.0 MIME-Version: 1.0 To: "Dr. H. Nikolaus Schaller" , Lars-Peter Clausen CC: Belisko Marek , Jean-Christophe PLAGNIOL-VILLARD , LKML , "linux-omap@vger.kernel.org" , Subject: Re: [PATCH] omapdss: Add new panel driver for Topolly td028ttec1 LCD. References: <1381352915-17219-1-git-send-email-marek@goldelico.com> <525662F5.3090600@ti.com> <7FAC77D4-5E1E-4B11-B067-3A8233C69240@goldelico.com> <52568B40.4040802@ti.com> <04AC7291-38E4-421B-979C-BF03D52E94BD@goldelico.com> <525699EF.6090803@ti.com> <52569CE8.5070201@metafoo.de> <5256F8DF.2020801@metafoo.de> <5257815F.5070803@ti.com> <5257A402.5030806@metafoo.de> <5570E6D7-4F66-40BE-A50C-6CCA8074BD83@goldelico.com> <5257B420.10808@ti.com> <5257BFA3.9090202@metafoo.de> In-Reply-To: X-Enigmail-Version: 1.5.2 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="u3ULf2lU2iPNkLxvIBM23uOHliFiIcV4r" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3784 Lines: 93 --u3ULf2lU2iPNkLxvIBM23uOHliFiIcV4r Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 11/10/13 12:50, Dr. H. Nikolaus Schaller wrote: > Hm. Is this a SPI or does it just look like one? Or is it some - otherw= ise > unknown - "3 wire serial interface". Or is it a "3(+1) GPIO slave devic= e"? > I am still not sure about this. Lars-Peter said "Back in the OpenMoko days we used the panel in normal 4-wire SPI mode with the GPIO bitbang SPI master." I don't know much about SPI, so I can't answer to that. If the serial bus is indeed not any kind of more or less standard SPI version, but really a custom bus for this controller, then the case is a bit unclear. > If we really want to do it correctly, we may have to write a driver for= that > special serial protocol as well. If it turns out that we can't mis-use = and tweak > it into a standard SPI driver with bit-bang backend. >=20 > I simply fear that we get dependencies with the SPI subsystem and have > to test, debug and maintain it. Maintaining the GPIO thing we currently= have > is easy. >=20 > What would be against taking the GPIO approach first and then upgrade a= s soon > as someone raises his/her finger that he/she wants to really interface = this display > differently and is not happy with the 3/4 GPIOs? Either they come up wi= th a patch > or contact the driver author (=3Dme). I don't have anything against that as long as we use only platform data. But DT data is not an in-kernel API, it's an external API. Once we define that the DT data for this panel is something, that's it, we should stick to it. Of course, we can build compatibility layers for old DT data, but I would avoid that if at all possible. If we now create the DT data with gpios, and the panel as platform device, it'd be rather nasty change to make it a child of an spi bus. (I presume, I have never made such a change). And, as the gpios and platform device approach is clearly wrong way to describe the hardware, I'm quite against using that description in the DT data. That said, one option is to describe the hardware correctly in the DT data, but have a platform device for the panel, with panel driver doing the bitbanging. In that case it is possible to update the system to use SPI framework if needed, without changing the DT data. However, I'm not sure how easy that would be. Tomi --u3ULf2lU2iPNkLxvIBM23uOHliFiIcV4r Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iQIcBAEBAgAGBQJSV85VAAoJEPo9qoy8lh71DgAP/AnqVBWIgsAhDTk+S/3r+ReD te5oZeuzHKREeVq5aY5MBXgWedUqrAI1bNip/pUox3g7b0v+fHSf2ONR80ijDynF YaKeA6MvGAOhmVrpKA3BOP4AK5DEfAK0KQk8tTfjT5Jufe9wk0F92XtqMKEzM50r mCy/WQ01IxIu7eqMuVGqwbs7uss13TlWqUSs1As9ri1Yhq3CufZY036QZppvDoG1 P7Nbp+PovXyyGepUWban7s/z5+h8P0gISGDKMyLrqv3h3CACG4iG9DCcgK8jNiE8 IFt8XTxk/Nhr/cK6t+QI6/wMsYzdz5tHcFjXMuei16fOgnipAmQGJ4AARRG9I1WG EhwKFty6qcbCsJOq2uN+DV9UrUXaW/a0NOj+Fe9Ai100RvJx0/dvyWukSZiPgGZk l+cpBGzCC0JkUo3bGXProu72SUZEG+HZnfcyT4rFWQDzJB8Uf0jKwjMw9Z3QOiZB LbKmHng2TFSqOQ42UkC1yvrMZEY4EWD2h1R4c70bgga3Z9OcPjHKNj7jVZhB4Ebn krP/V7HrAqnLbcWbY0Y70Tgysrd/NXdbmk1hs0rhJsl1m/XQb4knf2Sd5WYWXFQ6 WeuFQBtuFtUPFKFv+aq8sK/9CZJkKcOO/AvmHAuptsrS8sfecuazplMVLuXAW666 bV9RuamRmCguHoJYsiW2 =a7eW -----END PGP SIGNATURE----- --u3ULf2lU2iPNkLxvIBM23uOHliFiIcV4r-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/