From: Eric Anholt <eric@anholt•net>
To: Stefan Wahren <stefan.wahren@i2se•com>,
Annaliese McDermond <nh6z@nh6z•net>,
f.fainelli@gmail•com, wsa@the-dreams•de,
linux-i2c@vger•kernel.org, linux-rpi-kernel@lists•infradead.org,
linux-arm-kernel@lists•infradead.org
Cc: team@nwdigitalradio•com
Subject: Re: [PATCH v3] i2c: bcm2835: Model Divider in CCF
Date: Tue, 04 Jun 2019 12:26:44 -0700 [thread overview]
Message-ID: <87pnnt6tjf.fsf@anholt.net> (raw)
In-Reply-To: <31580e1f-60d2-f13b-dcfe-6bc6e75e9285@i2se.com>
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Stefan Wahren <stefan.wahren@i2se•com> writes:
> Am 29.05.19 um 06:29 schrieb Annaliese McDermond:
>> 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>
FWIW, also:
Reviewed-by: Eric Anholt <eric@anholt•net>
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next prev parent reply other threads:[~2019-06-04 19:27 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-29 4:29 [PATCH v3] i2c: bcm2835: Model Divider in CCF Annaliese McDermond
2019-06-02 7:40 ` Stefan Wahren
2019-06-04 19:26 ` Eric Anholt [this message]
2019-06-07 22:38 ` Wolfram Sang
2019-06-08 17:14 ` [PATCH v4] " Annaliese McDermond
2019-06-12 10:41 ` Wolfram Sang
2019-06-13 5:09 ` Annaliese McDermond
2019-06-13 7:50 ` Wolfram Sang
2019-06-19 7:16 ` Stefan Wahren
2019-06-19 7:56 ` Annaliese McDermond
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