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From: "FIXED-TERM Buecheler Konstantin (ETAS-SEC/ECT-Mu)"  <fixed-term.Konstantin.Buecheler@escrypt.com>
To: Patrick Menschel <menschel.p@posteo.de>,
	Marc Kleine-Budde <mkl@pengutronix.de>,
	"linux-can@vger.kernel.org" <linux-can@vger.kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>
Cc: Dan Murphy <dmurphy@ti.com>
Subject: AW: can: tcan4x5x: spi bits_per_word issue on Raspberry PI
Date: Fri, 16 Aug 2019 08:26:16 +0000
Message-ID: <47108d803086402c83d1073f3e3a62bb@escrypt.com> (raw)
In-Reply-To: <e6577cc2-89fc-9428-b73e-47f41eff2949@posteo.de>

> >> Now I have another really confusing problem. Anything I write to SPI is written little endian. The tcan chip expects big endian.
> >> Anything I read from SPI is treated as little endian but is big endian. Does anyone know why this happens?
> >> Is there a flag or something I can set for the SPI device/wire to fix this?
> >
> > Have you changed the bits_per_word to 8? Then you read just a stream
> > of bytes. If you tread them as an u32 they are in host order.
> >

@Marc
Yes, I changed bits_per_word to 8. Since the PI does not support any values apart from 
8 and 9 this seems to be the only way.

> > Marc
> >
> 
> 
> Hi,
> 
> from my experience with SPIDEV on RPI, the driver uses a char array for I/O.
> As the RPI code is build little endian, logically little endian comes out of SPI. You
> basically have to invert the bit and byte order by hand for a big endian slave.
> 

@Patrick, Marc
You both are right. This seems to be the problem. The SPI driver uses char arrays
and the tcan driver treats them as u32. 

I will try to change the byte order by hand to get it running for my project. But in the long 
run, this does not seem to be a proper solution... 

Regards, 
Konstantin 


> Clock Phase and Clock Polarity are also an issue on the RPI as at least SPIDEV
> kindly overlooks any options set previously.
> I had my share of this while writing a test app for a MAX31855 IC and ended up
> casting a little endian array to a big endian structure.
> 
> Regards,
> Patrick


  parent reply index

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-14 15:01 FIXED-TERM Buecheler Konstantin (ETAS-SEC/ECT-Mu)
2019-08-15  8:34 ` Marc Kleine-Budde
     [not found]   ` <e6577cc2-89fc-9428-b73e-47f41eff2949@posteo.de>
2019-08-16  8:26     ` FIXED-TERM Buecheler Konstantin (ETAS-SEC/ECT-Mu) [this message]
2019-08-16  8:37       ` AW: " Marc Kleine-Budde

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