linux-kernel - Re: [PATCH v3 3/3] i2c: designware: do not disable adapter after transfer

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Date:	Tue, 16 Aug 2016 17:00:20 +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>
Subject: Re: [PATCH v3 3/3] i2c: designware: do not disable adapter after
 transfer

Hi, + Wolfram

On 07/29/2016 01:03 AM, Lucas De Marchi wrote:
> Disabling the adapter after each transfer adds additional delays
> for each I2C transfer. Even if we don't wait for it to be disabled
> anymore, on next transfer we will need to if we have several transfers
> in a row.
>
> Now during the transfer init we check if IC_TAR can be changed
> dynamically, the status register for no activity and TX buffer being
> empty. In this case we don't need to disable it
>
> When a transfer fails the adapter will still be disabled - this is a
> conservative approach. When transfers succeed, the adapter is left
> enabled and it's configured so to disable interrupts.
>
> Alternating register reads on 2 slaves:
> perf stat -r4 chrt -f 10 ./i2c-test /dev/i2c-1 25000 0x40 0x6 0x1e 0x00
>
> Before:
> 	8.638705161 seconds time elapsed                  ( +-  5.90% )
> After:
> 	7.516821591 seconds time elapsed                  ( +-  0.11% )
>
> Signed-off-by: Lucas De Marchi <lucas.demarchi@...el.com>
> Signed-off-by: José Roberto de Souza <jose.souza@...el.com>
> ---
>  drivers/i2c/busses/i2c-designware-core.c | 55 +++++++++++++++++++++-----------
>  1 file changed, 37 insertions(+), 18 deletions(-)
>
Acked-by: Jarkko Nikula <jarkko.nikula@...ux.intel.com>