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Subject: Re: [PATCH v2 5/6] i2c: i2c-stm32f7: Add DMA support
To:     Wolfram Sang <wsa@the-dreams.de>
CC:     Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        Alexandre Torgue <alexandre.torgue@st.com>,
        <linux-i2c@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>
References: <1521650940-11651-1-git-send-email-pierre-yves.mordret@st.com>
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 <20180403153925.lg37rezuvs6hefks@ninjato>
From:   Pierre Yves MORDRET <pierre-yves.mordret@st.com>
Message-ID: <273ac8d2-6861-c1ad-c2fc-f9c5cc2ac3de@st.com>
Date:   Wed, 4 Apr 2018 10:20:44 +0200
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On 04/03/2018 05:39 PM, Wolfram Sang wrote:
> 
>> +#define STM32F7_I2C_DMA_LEN_MIN			0x1
> ...
> 
>> +	if (i2c_dev->dma && f7_msg->count >= STM32F7_I2C_DMA_LEN_MIN) {
> 
> Are you using DMA for every message with a length >= 1? The setup of
> that might be more expensive than the DMA gain, if so.
> 
Well yes. I am in charge of DMA IPs as well. I2C is the only devices that I had
to test DMA outside standard DMA Engine test. Quite convenient.
I believe to stress both I2C and DMA, this value was relevant.
Now I agree this value can be tuned a little bit. I might raise this threshold
in V3.