linux-kernel - Re: [PATCH] Add Dallas DS1390 RTC chip

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Date:	Fri, 17 Oct 2008 08:29:06 -0700
From:	David Brownell <david-b@...bell.net>
To:	Mark Jackson <mpfj@...c.co.uk>
Cc:	Alessandro Zummo <alessandro.zummo@...ertech.it>,
	rtc-linux@...glegroups.com, lkml <linux-kernel@...r.kernel.org>,
	spi-devel-general@...ts.sourceforge.net
Subject: Re: [PATCH] Add Dallas DS1390 RTC chip

On Friday 17 October 2008, Mark Jackson wrote:
> >> +    /* Can tx_buf and rx_buf be equal? The doc in spi.h is not sure... */
> >> +    xfer.tx_buf = chip->tx_buf;
> >> +    xfer.rx_buf = chip->rx_buf;
> > 
> >  you use the same buffer a few functions below. either
> >  one way or the other. please investigate with the spi subsystem maintainer.
> 
> David,
> 
> Just to double check (as per Alessandro's suggestion), is this okay use of the 
> spi buffers ?

Yes.  That comment deserves to be updated.

SPI does bi-directional I/O, and the underlying controller
should be able to just replace the contents of a buffer
with a spi_transfer that uses the same rx and tx buffers.

- Dave
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