Re: [PATCH v4] i2c: bcm2835: Model Divider in CCF

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

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On Sat, Jun 08, 2019 at 10:14:43AM -0700, Annaliese McDermond wrote:
> Model the I2C bus clock divider as a part of the Core Clock Framework.
> Primarily this removes the clk_get_rate() call from each transfer.
> This call causes problems for slave drivers that themselves have
> internal clock components that are controlled by an I2C interface.
> When the slave's internal clock component is prepared, the prepare
> lock is obtained, and it makes calls to the I2C subsystem to
> command the hardware to activate the clock.  In order to perform
> the I2C transfer, this driver sets the divider, which requires
> it to get the parent clock rate, which it does with clk_get_rate().
> Unfortunately, this function will try to take the clock prepare
> lock, which is already held by the slave's internal clock calls
> creating a deadlock.
> 
> Modeling the divider in the CCF natively removes this dependency
> and the divider value is only set upon changing the bus clock
> frequency or changes in the parent clock that cascade down to this
> divisor.  This obviates the need to set the divider with every
> transfer and avoids the deadlock described above.  It also should
> provide better clock debugging and save a few cycles on each
> transfer due to not having to recalcuate the divider value.
> 
> Signed-off-by: Annaliese McDermond <nh6z@nh6z.net>
> Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
> Reviewed-by: Eric Anholt <eric@anholt.net>

Applied to for-next, thanks for keeping at this! And thanks to all
reviewers, too.

(One minor thing: next time, please start a new thread when sending a
new patch. This makes applying patches easier.)


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