linux-kernel - Re: mc13xxx-core: kernel hangs after 'regmap

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Message-ID: <20120524214229.1038515zms1khf6t@webmail.epfl.ch>
Date:	Thu, 24 May 2012 21:42:29 +0200
From:	philippe.retornaz@...l.ch
To:	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Cc:	Fabio Estevam <festevam@...il.com>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>, marc@...esign.com.au,
	Shawn Guo <shawn.guo@...escale.com>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Sascha Hauer <kernel@...gutronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: mc13xxx-core: kernel hangs after 'regmap_read'

Mark Brown <broonie@...nsource.wolfsonmicro.com> a écrit :

> On Thu, May 24, 2012 at 02:39:02PM -0300, Fabio Estevam wrote:
>> On Thu, May 24, 2012 at 1:41 PM, Uwe Kleine-König
>
>> > The imx spi driver can do both (GPIO and hardware CS) because not all
>> > pins that can do hardware CS are available as GPIO.
>
>> Right, unfortunately on mx31 the SPI CS pins cannot be used as GPIOs.
>
>> On mx51evk the SPI CS are used as GPIOs and that probably explains why
>> it worked on mx51evk and fails on mx31pdk.
>
> Oh dear, this affects regmap but it'll probably also affect other things
> - how plausible is it that we'll be able to fix in the driver (assuming
> it's not just hardware misprogramming)?  We can probably manage to come
> up with something for regmap but it's the wrong level to fix things.
>

Sadly, after looking at the imx31 datasheet it seems it's a hardware  
limitation. We could maybe workaround it by using DMA to access the  
CSPI but even with dma, this would need a single transfer in order to  
keep the CS signal asserted.

Thus, we need to workaround this in the regmap-spi or mc13783-spi driver.
Either we find a way to have regmap-spi to use 32bits transfert or we  
implement a custom bus inside mc13783-spi.

Thanks,

Philippe
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