Re: [PATCH] i2c-s3c2410: Leave the bus disabled unless it is in use

[Wolfram Sang <wsa@the-dreams.de>]

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On Fri, Feb 07, 2014 at 02:24:09PM +0530, Naveen Krishna Chatradhi wrote:
> From: Simon Glass <sjg@chromium.org>
> 
> There is a rather odd feature of the exynos i2c controller that if it
> is left enabled, it can lock itself up with the clk line held low.
> This makes the bus unusable.
> 
> Unfortunately, the s3c24xx_i2c_set_master() function does not notice
> this, and reports a timeout. From then on the bus cannot be used until
> the AP is rebooted.
> 
> The problem happens when any sort of interrupt occurs (e.g. due to a
> bus transition) when we are not in the middle of a transaction. We
> have seen many instances of this when U-Boot leaves the bus apparently
> happy, but Linux cannot access it.
> 
> The current code is therefore pretty fragile.
> 
> This fixes things by leaving the bus disabled unless we are actually
> in a transaction. We enable the bus at the start of the transaction and
> disable it at the end. That way we won't get interrupts and will not
> lock up the bus.
> 
> It might be possible to clear pending interrupts on start-up, but this
> seems to be a more robust solution. We can't service interrupts when
> we are not in a transaction, and anyway would rather not lock up the
> bus while we try.
> 
> Signed-off-by: Simon Glass <sjg@chromium.org>
> Cc: Grant Grundler <grundler@chromium.org>
> Signed-off-by: Naveen Krishna Chatradhi <ch.naveen@samsung.com>
> Acked-by: Kyungmin Park <kyungmin.park@samsung.com>

Applied to for-next, thanks!


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