linux-kernel - Re: [PATCH] spi: spi-davinci: deassert CS on setup()

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Message-ID: <CA+5vRUXL6HR5NNopxWb7XP9PFg49t8yXOJdg4f3epVqmWKyDbQ@mail.gmail.com>
Date:	Thu, 12 Sep 2013 09:01:48 -0400
From:	Ben Gardiner <ben.l.gardiner@...il.com>
To:	Trent Piepho <tpiepho@...il.com>
Cc:	Grant Likely <grant.likely@...retlab.ca>,
	"spi-devel-general@...ts.sourceforge.net" 
	<spi-devel-general@...ts.sourceforge.net>,
	davinci-linux-open-source@...ux.davincidsp.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] spi: spi-davinci: deassert CS on setup()

Hi Trent,

Thanks for the quick review.

On Tue, Sep 10, 2013 at 10:44 PM, Trent Piepho <tpiepho@...il.com> wrote:
>
> It is supposed to be possible to call setup() on one slave while
> transfers on another slave attached to the same master are in
> progress.
>
> A cursory look at the code makes it seem that all the CS control bits
> share SPIDAT1?  Will writing to SPIDAT1 in davinci_spi_chipselect()
> cause a race if another chipselect is being used?

Good point. I think you're right there could be a race.

I tested with multiple slaves and hammered the bus with concurrent
accesses; but that doesn't mean that there _isn't_ still a race.

Can you recommend an existing implementation in-tree upon which I can
base a new patch to add concurrency protection to SPIDAT1 accesses?
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