From: Ben Dooks <ben@simtec.co.uk>
To: Ben Gamari <bgamari@gmail.com>
Cc: beagleboard <beagleboard@googlegroups.com>,
linux-omap <linux-omap@vger.kernel.org>,
David Brownell <dbrownell@users.sourceforge.net>,
Eric Miao <eric.miao@marvell.com>,
Michael Hennerich <michael.hennerich@analog.com>,
Grant Likely <grant.likely@secretlab.ca>,
spi-devel-general@lists.sourceforge.net
Subject: Re:
Date: Thu, 21 Jan 2010 09:04:30 +0900 [thread overview]
Message-ID: <4B579A0E.4030108__46446.1063886576$1264085152$gmane$org@simtec.co.uk> (raw)
In-Reply-To: <1264016711-sup-309@ben-laptop>
Ben Gamari wrote:
> Bcc:
> Subject: GPIO chip select support in omap2_mcspi driver
>
> Hey,
>
> Recently I have been looking to use a BeagleBoard to drive several
> serial ADCs and DACs in a data acquisition and analysis setup. Unfortunately, the
> BeagleBoard is severely limited by the number of SPI controllers it
> exposes on the expansion connector (McSPI3 with 2 CS lines and McSPI4
> with one). This is insufficient for our application and thus I have been
> investigating adding support to the mcspi driver for using GPIO lines as
> chip select lines, as is done in the pxa2xx, bfin5xx, and s3c24xx drivers.
>
> To this end, I have a few questions about how this support was
> implemented. First, it seems that the s3c24xx driver is built on the
> spi_bitbang driver, despite interfacing with a dedicated hardware SPI
> controller. What is the reason for this? Was this done specifically for
> the purpose of incorporating support for GPIO CS pins?
The spi_bitbang driver also has a really useful spi queue and workqueue
built into it, which is what the s3c24xx spi driver actually bothers to
use.
> It seems like the rough idea is to add a cs_gpio field to the device
> struct (omap2_mcspi) and add the appropriate code to the
> omap2_mcspi_force_cs() to bring cs_gpio high or low if it is valid. The
> potential problem I can see with this is that omap2_mcspi_set_enable()
> is called to enable the channel before the force_cs() is called (in
> omap2_mcspi_work()). If I'm interpreting the documentation correctly,
> the enable bit starts the clocks, meaning that the chip will begin
> clocking out data before CS is brought high. I must be missing something
> here, no?
>
> For reference, I included a short list of relevant commits below, largely for
> my own benefit. I would greatly appreciate any feedback you might have.
>
> Thanks,
> - Ben
>
>
> pxa2xx_spi: a7bb3909b3293d503211d7f6af8ed62c1644b686
> bfin_spi: 42c78b2bf51bafb4cfa98dfecc28dd9b8bcd04b0
next prev parent reply other threads:[~2010-01-21 0:04 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-01-20 19:47 (no subject) Ben Gamari
2010-01-21 0:04 ` Ben Dooks [this message]
2010-01-21 0:04 ` Ben Dooks
2010-01-21 0:04 ` Ben Dooks
2010-01-22 15:53 ` Re: Ben Gamari
2010-01-28 4:10 ` McSPI questions pertaining to GPIO chip select support Ben Gamari
[not found] ` <1264651770-sup-5197@ben-laptop>
2010-01-28 4:15 ` Bill Gatliff
2010-01-28 4:25 ` Ben Gamari
2010-01-28 4:27 ` Bill Gatliff
2010-01-28 4:33 ` jassi brar
[not found] ` <1b68c6791001272033q60dd31dbif4de285cd9bac83d-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2010-01-29 0:32 ` Ben Gamari
2010-01-29 1:09 ` jassi brar
[not found] ` <1b68c6791001281709l7d11da30lee486632e85b99cb-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2010-01-29 1:58 ` Ben Gamari
2010-12-21 17:56 ` [RFC PATCH] GPIO chip select support for McSPI Ben Gamari
2010-12-21 17:56 ` [PATCH] mcspi: Add support for GPIO chip select lines Ben Gamari
[not found] ` <1292954195-20204-2-git-send-email-bgamari.foss@gmail.com>
2010-12-23 19:59 ` Tony Lindgren
2010-12-23 21:38 ` Grant Likely
2010-12-23 23:09 ` Ben Gamari
2010-12-24 0:37 ` Grant Likely
2010-12-24 2:27 ` Ben Gamari
2010-12-24 3:28 ` Grant Likely
2010-12-24 6:05 ` Ben Gamari
2011-02-12 8:33 ` Grant Likely
2011-02-13 22:07 ` Ben Gamari
2011-08-30 10:14 ` McSPI questions pertaining to GPIO chip select support Raju Sana
2011-08-30 13:50 ` Ben Gamari
2011-08-30 13:50 ` [PATCH] mcspi: Add support for GPIO chip select lines Ben Gamari
2011-08-30 13:52 ` [PATCH] beagledaq: Hack in cs_gpios Ben Gamari
[not found] ` <1314712343-27367-1-git-send-email-bgamari.foss-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2011-09-05 12:42 ` Raju Sana
2015-09-01 12:01 Zariya
2015-09-01 16:06 Re: Zariya
2017-02-23 15:09 Qin's Yanjun
2017-11-13 14:55 Amos Kalonzo
2020-02-06 6:36 Re: Viviane Jose Pereira
2020-02-11 22:34 (unknown) Rajat Jain
[not found] ` <20200211223400.107604-1-rajatja-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2020-02-12 9:30 ` Jarkko Nikula
[not found] ` <b3397374-0cb8-cf6c-0555-34541a1c108c-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
2020-02-12 10:24 ` Re: Andy Shevchenko
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