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From: David Brownell <david-b@pacbell.net>
To: Daniel Ribeiro <drwyrm@gmail.com>
Subject: Re: [spi-devel-general] [patch 05/14] mfd: PCAP2 driver
Date: Sat, 22 Nov 2008 20:59:59 -0800
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Cc: Stefan Schmidt <stefan@datenfreihafen.org>,
       spi-devel-general@lists.sourceforge.net,
       Stefan Schmidt <stefan@openmoko.org>, eric.y.miao@gmail.com,
       linux-kernel@vger.kernel.org, sameo@openedhand.com,
       linux-arm-kernel@lists.arm.linux.org.uk
References: <20081121160403.073751031@dodger.lab.datenfreihafen.org> <200811221819.53186.david-b@pacbell.net> <1227411537.3148.22.camel@brutus>
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On Saturday 22 November 2008, Daniel Ribeiro wrote:
> > ?- You should make ezx_pcap_write() and ezx_pcap_read() switch
> > ? ?over to spi_write_then_read(), to ensure it's never doing
> > ? ?DMA to/from the stack. ?I see a byte-order dependency too...
> 
> I tried spi_write_then_read before, but it didn't work. I supposed it
> was because it was doing 2 transfers as the second transfer rx_buf
> always came zeroed.

You may have been using it wrong.  Also, verify against
current kernels ... there have been bugfixes to pxa2xx_spi.


> I see that commit 
> f9b90e39cbc5c4d6ef60022fd1f25d541df0aad1 changed it to do a single
> transfer, so i will try it again.

Unless it needs the full duplex capability of SPI, then
you should be able to make write_then_read work ... on
the other hand, if you do need full duplex, then you
should address the DMA.  (And byteswapping, either way.)


> > ?- If you're going to mark the probe() as __devinit, then mark
> > ? ?the remove() as __devexit and use __devexit_p() in the driver
> > ? ?struct.
> 
> Ok. Shouldn't i use __init instead?

I wouldn't.  There are ways that the probe() could be called
more than once -- e.g. after rebinding either of the relevant
SPI drivers through sysfs, or after rmmod/modprobe of the SPI
master controller driver -- and using an __init annotation
would make that point to memory that's unlikely to still hold
that code.

- Dave
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