From mboxrd@z Thu Jan  1 00:00:00 1970
From: pierre-yves.mordret@st.com (Pierre Yves MORDRET)
Date: Wed, 4 Apr 2018 10:20:44 +0200
Subject: [PATCH v2 5/6] i2c: i2c-stm32f7: Add DMA support
In-Reply-To: <20180403153925.lg37rezuvs6hefks@ninjato>
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 <1521650940-11651-6-git-send-email-pierre-yves.mordret@st.com>
 <20180403153925.lg37rezuvs6hefks@ninjato>
Message-ID: <273ac8d2-6861-c1ad-c2fc-f9c5cc2ac3de@st.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org



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.