Re: i2c-imx.c: Unnecessary delay slowing down i2c communication

[Wolfram Sang <wsa@kernel.org>]

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On Thu, Mar 03, 2022 at 03:19:00PM +0000, Ian Dannapel wrote:
> Hello I²C Driver Maintainers,

Adding the i2c-imx maintainer to CC.

> 
> please excuse me if I am not following the right steps to report a question. I did not find consensus between all instructions that I read.
> 
> We noted that on the IMX i2c driver, at the i2c_imx_start funtion, some sleep/delay was introduced without any apparent reason:
> Line 448 at:  https://github.com/Freescale/linux-fslc/commit/3a5ee18d2a32bda6b9a1260136f6805848e3839d 
> Line 528 at:  https://github.com/Freescale/linux-fslc/commit/2b899f34e1db9adef8716d07e872a800dfa60790
> Line 200 at:  https://github.com/Freescale/linux-fslc/commit/43309f3b521302bb66c4c9e66704dd3675e4d725
> 
> This sleep causes a pretty big latency overhead on I²C writes and no IMX8MP document states the need of this delay on the controller. NXP Support also informed that this delay might not be needed.
> Some early tests with removing this delay completely showed a great reduction on the write latency and no problems with the communication.
> 
> But since we want a stable and fast communication, I ask here again if someone knows the reason or the need for this delay when starting to communicate on the I2C bus.
> 
> I appreciate any response and if further information is needed, I can gladly report it.
> 
> 
> Best regards,
> Ian Dannapel
> ian.dannapel@iris-sensing.com
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> infrared & intelligent sensors
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> 
> 
> 
> 
> 

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