From: thomas.petazzoni@free-electrons.com (Thomas Petazzoni)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 5/8] gpio: 74x164: Add output pin support
Date: Wed, 5 Sep 2012 13:56:46 +0200 [thread overview]
Message-ID: <20120905135646.3bbf98fa@skate> (raw)
In-Reply-To: <20120905122652.7c752e96@eb-e6520>
Le Wed, 5 Sep 2012 12:26:52 +0200,
Eric B?nard <eric@eukrea.com> a ?crit :
> Le Wed, 5 Sep 2012 12:09:06 +0200,
> Thomas Petazzoni <thomas.petazzoni@free-electrons.com> a ?crit :
> > I don't think the /OE pin can be used as a chip select, because when it
> > is high, the state of the output pins is not maintained to their
> > previous state: the pins are turned into the high impedance state. If
> > used as a chip select, it would mean that the value of the output pins
> > transition from their old state to high impedance at the beginning of
> > the transfer, and then from the high impedance to their new state at
> > the end of the transfer.
>
> OK that's exactly what I was thinking to ;-)
Good. So, do you think it's reasonable to use the STCP as a chip-select
for this device?
> > And of course, this signal is inverted compared to a normal chip select.
>
> polarity of the chip select can vary (mc13xxx-spi has an active high CS
> for example).
Sure, but I guess it depends on capabilities of the SPI controller in
your SoC. I haven't seen a way of configuring the polarity of the chip
selects in the i.MX28 SPI controller, but maybe I've missed it.
Anyway, /OE isn't usable as a chip-select, so we don't care.
Best regards,
Thomas
--
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
next prev parent reply other threads:[~2012-09-05 11:56 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-05 8:40 [PATCH 1/8] gpio: 74x164: Use module_spi_driver boiler plate function Maxime Ripard
2012-09-05 8:40 ` [PATCH 2/8] gpio: 74x164: Use devm_kzalloc Maxime Ripard
2012-09-05 8:46 ` Florian Fainelli
2012-09-05 9:16 ` Thomas Petazzoni
2012-09-06 7:22 ` Linus Walleij
2012-09-07 21:02 ` Linus Walleij
2012-09-05 8:40 ` [PATCH 3/8] gpio: 74x164: Remove platform data and use dynamic gpio number assignment Maxime Ripard
2012-09-05 8:48 ` Florian Fainelli
2012-09-05 9:15 ` Thomas Petazzoni
2012-09-05 9:17 ` Thomas Petazzoni
2012-09-05 8:40 ` [PATCH 4/8] gpio: 74x164: Add device tree support Maxime Ripard
2012-09-05 8:50 ` Florian Fainelli
2012-09-05 9:17 ` Thomas Petazzoni
2012-09-06 7:22 ` Linus Walleij
2012-09-05 8:40 ` [PATCH 5/8] gpio: 74x164: Add output pin support Maxime Ripard
2012-09-05 9:20 ` Thomas Petazzoni
2012-09-05 9:46 ` Eric Bénard
2012-09-05 10:09 ` Thomas Petazzoni
2012-09-05 10:26 ` Eric Bénard
2012-09-05 11:56 ` Thomas Petazzoni [this message]
2012-09-05 12:22 ` Eric Bénard
2012-09-05 12:29 ` Thomas Petazzoni
2012-09-05 12:54 ` Eric Bénard
2012-09-05 13:02 ` Maxime Ripard
2012-09-05 13:27 ` Eric Bénard
2012-09-05 8:40 ` [PATCH 6/8] gpio: 74x164: Add support for daisy-chaining Maxime Ripard
2012-09-05 8:56 ` Thomas Petazzoni
2012-09-05 8:40 ` [PATCH 7/8] gpio: 74x164: dts: Add documentation for the dt binding Maxime Ripard
2012-09-05 8:40 ` [PATCH 8/8] ARM: dts: cfa10049: Add the 74HC595 gpio expanders Maxime Ripard
2012-09-05 8:46 ` [PATCH 1/8] gpio: 74x164: Use module_spi_driver boiler plate function Florian Fainelli
2012-09-05 9:16 ` Thomas Petazzoni
2012-09-06 7:21 ` Linus Walleij
2012-09-06 14:10 ` Maxime Ripard
2012-09-07 21:09 ` Linus Walleij
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