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From: Ben Dooks <ben-Y5A6D6n0/KfQXOPxS62xeg@public.gmane.org>
To: Ben Gamari <bgamari-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Cc: beagleboard <beagleboard-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org>,
	linux-omap <linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	David Brownell
	<dbrownell-Rn4VEauK+AKRv+LV9MX5uipxlwaOVQ5f@public.gmane.org>,
	Eric Miao <eric.miao-eYqpPyKDWXRBDgjK7y7TUQ@public.gmane.org>,
	Michael Hennerich
	<michael.hennerich-OyLXuOCK7orQT0dZR+AlfA@public.gmane.org>,
	Grant Likely
	<grant.likely-s3s/WqlpOiPyB63q8FvJNQ@public.gmane.org>,
	spi-devel-general-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
Subject: Re:
Date: Thu, 21 Jan 2010 09:04:30 +0900	[thread overview]
Message-ID: <4B579A0E.4030108__299.369081813161$1264032479$gmane$org@simtec.co.uk> (raw)
In-Reply-To: <1264016711-sup-309@ben-laptop>

[-- Attachment #1: Type: text/plain, Size: 1981 bytes --]

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


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  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
2010-01-21  0:04 ` (no subject) Ben Dooks
2010-01-21  0:04 ` Ben Dooks [this message]
2010-01-22 15:53 ` 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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