linux-kernel - Re: [PATCH] spi-gpio: Implement spidelay() for busses that need it.

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Date:	Mon, 16 Feb 2009 12:42:27 -0800
From:	David Brownell <david-b@...bell.net>
To:	Michael Buesch <mb@...sch.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] spi-gpio: Implement spidelay() for busses that need it.

[
  NOTE:  removed openwrt from the cc list, it rejects posts
  from non-subscribers.  Please don't cc such lists.
]

On Sunday 15 February 2009, Michael Buesch wrote:
> + * NOTE:  to clock "as fast as we can", set spi_device.max_speed_hz
> + * and spi_transfer.speed_hz to 0.

Won't work; if spi->max_speed_hz is zero, spi_async() and
friends will refuse to queue any messages.

I'm not averse to a solution that lets some boards use a
slowed-down bitbang loop.  But it would be a lot easier
if you kept the default the way it is, and just added
that slowdown as an option for the existing customization
case (currently oriented towards speedup, not slowdown).

- Dave
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