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List:       linaro-kernel
Subject:    Re: [PATCH] spi: Add a timeout when waiting for transfers
From:       Mark Brown <broonie () kernel ! org>
Date:       2014-01-31 12:26:17
Message-ID: 20140131122617.GC22609 () sirena ! org ! uk
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On Fri, Jan 31, 2014 at 01:00:31PM +0100, Geert Uytterhoeven wrote:

> One other thing: I haven't tried your patch yet, but I'm afraid the 10 ms
> may be too small.

> E.g. with PIO-based RSPI I don't get more than 2 Mbps, even though
> spi-max-frequency = <30000000>, due to the PIO and interrupt overhead.
> Hence a 1 MiB read would take ca. 4s, while your timeout would be 300 ms.

Hrm, I wouldn't have expected something doing PIO in more than one burst
to be letting the transfer run in the background.  Though I suppose that
might make sense in some situations...

I was wondering if that was cutting it a bit fine but more for scheduler
reasons, it's what the s3c64xx driver has been using for a while without
complaints but may not translate so well with greater exposure.

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