linux-kernel - Re: [PATCH v3 1/3] i2c: designware: wait for disable/enable only if necessary

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Message-ID: <bb134298-26de-c565-bf7a-78302914991f@linux.intel.com>
Date:	Tue, 16 Aug 2016 16:59:55 +0300
From:	Jarkko Nikula <jarkko.nikula@...ux.intel.com>
To:	Lucas De Marchi <lucas.demarchi@...el.com>,
	linux-i2c@...r.kernel.org
Cc:	christian.ruppert@...tech.com, linux-kernel@...r.kernel.org,
	mika.westerberg@...ux.intel.com,
	José Roberto de Souza <jose.souza@...el.com>,
	Wolfram Sang <wsa@...-dreams.de>
Subject: Re: [PATCH v3 1/3] i2c: designware: wait for disable/enable only if
 necessary

Hi, + Wolfram

On 07/29/2016 01:03 AM, Lucas De Marchi wrote:
> From: José Roberto de Souza <jose.souza@...el.com>
>
> If we aren't going to continue using the controller we can just disable
> it instead of waiting for it to complete. The biggest improvement here
> is when a I2C transaction is completed and it doesn't block until
> the adapter is disabled. When a new transfer is needed we will disable
> and wait for its completion.
>
> This way the adapter will continue changing its state in parallel to the
> execution of the thread that requested the I2C transaction saving most
> of the time 25~250 usec per I2C transaction.
>
> A simple program doing a register read (1 byte write, 1 byte read)
> alternating on 2 different slaves repeated 25k times for each and
> measurements taken 4 times we get:
>
> perf stat -r4 chrt -f 10 ./i2c-test /dev/i2c-1 25000 0x40 0x6 0x1e 0x00
>
> Before:
> 	30.879317977 seconds time elapsed                 ( +- 14.83% )
> After:
> 	8.638705161 seconds time elapsed                  ( +-  5.90% )
>
> Signed-off-by: José Roberto de Souza <jose.souza@...el.com>
> Signed-off-by: Lucas De Marchi <lucas.demarchi@...el.com>
> ---
>  drivers/i2c/busses/i2c-designware-core.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
Acked-by: Jarkko Nikula <jarkko.nikula@...ux.intel.com>